JP4804767B2 - Ultra-short pulse laser transmitter - Google Patents

Description

  The present invention relates to an ultrashort pulse laser transmission device.

Conventionally, as a laser microscope, a scanning type multi-photon excitation laser microscope that irradiates a specimen to be observed with an ultra-short pulse laser beam and detects a chemical reaction or fluorescence due to multi-photon absorption of the specimen is known. .
The multiphoton excitation phenomenon occurs with a probability proportional to the nth power of unit area and photon density per unit time (n = 2 in the case of two-photon excitation, n = 3 in the case of three-photon excitation). As a light source for generating excitation, an ultrashort pulse laser beam of sub-picosecond order is usually used.

  However, such a sub-picosecond order pulsed laser beam is not a perfect single wavelength beam but has a wavelength width correlated with the pulse width of the laser beam. In general, when laser light passes through an optical system, the shorter the wavelength, the slower the speed in the medium, and the longer the wavelength, the faster the speed in the medium. Therefore, if the laser beam has a wavelength width as described above, when the laser beam passes through the optical system, there will be a difference in the transit time depending on the wavelength, and as a result, the laser before entering the optical system. A so-called positive chirp is generated in which the pulse width of the laser light after passing through the optical system is wider than the pulse width of the light.

As described above, since the multiphoton excitation phenomenon depends on the photon density, it is obtained as a result of reducing the probability of the multiphoton excitation phenomenon occurring due to the broadening of the pulse width of the laser light incident on the specimen surface due to the chirp. There was a problem that the fluorescence became dark.
As means for solving this problem, it is known to use means for adjusting chirp, so-called dispersion compensation optical system. As a dispersion compensation optical system, a prism pair, a grating pair, or an optical system in which these are combined is known (see Non-Patent Document 1 and Patent Documents 1 and 2).
Edited by Tadashi Sueda and Takeshi Kamiya, “Ultra High-Speed Electronics” Bafukan, 1991, p. 29-34 Japanese Patent Laid-Open No. 10-68889 Japanese Patent Laid-Open No. 11-218490

These dispersion compensation optical systems serve to generate a so-called negative chirp that delays the long wavelength component of the laser light from the short wavelength component, thereby correcting the positive chirp after passing through the medium.
Specifically, when a grating pair is used as the dispersion compensation optical system, when laser light is incident on the grating pair, −1st order diffracted light having angular dispersion is generated by the first grating on which the laser light is incident. . The −1st-order diffracted light is incident on a second grating, for example, disposed opposite to and parallel to the first grating, whereby the angular dispersion caused by the first grating is corrected, and the negative chirped laser beam. Is formed.

However, when laser light is incident on the grating pair, in addition to the above-described −1st order diffracted light, diffracted light of a different order is also generated. Since the diffraction angle of each order of diffracted light changes according to the wavelength of the incident laser light, depending on the wavelength of the laser light incident on the first grating, the diffracted light may return to the incident optical axis. There is.
The diffracted light (returned light) may be incident on a laser oscillator that emits laser light. In such a case, the laser oscillation in the laser oscillator may become unstable, which may cause a failure of the laser oscillator. was there.

In recent use of a scanning multiphoton excitation laser microscope, since there is a demand for changing the wavelength of laser light, use of a laser light source capable of changing the wavelength of emitted laser light has been studied. However, when the wavelength of the laser beam changes, the emission direction of the diffracted light by the grating changes. There was a problem that light was incident on the laser light source.
Note that the wavelength of the emitted laser light can be varied by changing the configuration in the laser oscillator.

  The present invention has been made in order to solve the above-described problem, and in a dispersion compensation optical system that generates negative chirp using a grating, it is possible to prevent the return light from the grating from entering the light source. An object is to provide a short pulse laser transmission device.

In order to achieve the above object, the present invention provides the following means.
The present invention provides a pulse dispersion comprising a light source that emits an ultrashort pulse laser beam, and a grating that is incident on the ultrashort pulse laser beam and that splits the ultrashort pulse laser beam in a plane perpendicular to the longitudinal direction of the groove. and compensator, the grating is tilted around an axis perpendicular to the plane, the return light directed from said pulse dispersion compensator to the source, and a entrance preventing portion to prevent incident on the light source, the pulse The dispersion compensator has a pair of gratings including a first grating disposed on the laser light source side and a second grating disposed opposite to the first grating, and the second grating includes The first grating whose rotation angle is adjusted when the wavelength is variable is adjusted to be parallel to each other and emitted from the second grating. An optical axis adjusting optical system that keeps the optical axis emitted from the pulse dispersion compensator coaxial according to the movement of the first-order or first-order diffracted light, and the optical axis adjusting optical system includes the first grating and the first grating A super- reflection unit provided separately from the second grating, and a moving unit that moves the total reflection unit according to the movement of the −1st-order or first-order diffracted light emitted from the second grating. A short pulse laser transmission device is provided.

According to the present invention, since the incidence prevention unit is provided, it is possible to prevent the return light from the grating of the pulse dispersion compensator from going to the light source from being blocked by the incidence prevention unit and entering the light source. Therefore, failure of the light source that emits the ultrashort pulse laser can be prevented.
Further, since the pulse dispersion compensator is provided with a grating, negative chirp can be generated in the ultrashort pulse laser beam by the grating.

Moreover, in the said invention, it is desirable that the said incident prevention part is a rectifier inserted in the optical path between the said light source and the said pulse dispersion compensator.
According to the present invention, by inserting the rectifying element between the light source and the pulse dispersion compensator, the ultrashort pulse laser beam traveling from the light source to the pulse dispersion compensator and the return light traveling from the pulse dispersion compensator to the light source are rectified. Incident on the element. Since the rectifying element transmits only the ultrashort pulse laser that goes to the pulse dispersion compensator and blocks the return light that goes to the light source, the return light can be prevented from entering the light source.

Furthermore, in the above invention, it is preferable that the rectifying element is an isolator inserted in an optical path between the light source and the pulse dispersion compensator.
According to the present invention, since the isolator is inserted between the light source and the pulse dispersion compensator, only the ultrashort pulse laser beam directed to the pulse dispersion compensator is transmitted, and the return light toward the light source is blocked. It is possible to prevent light from entering the light source.
Specifically, one of the linearly polarized light beams incident on the isolator from the light source side is polarized to the other linearly polarized light and emitted to the pulse dispersion compensator side. The other linearly polarized light incident on the isolator from the pulse dispersion compensator side is prevented from entering the light source by the isolator.

In the above invention, the rectifying element includes a polarizing element that is inserted in an optical path between the light source and the pulse dispersion compensator and transmits only one of linearly polarized light orthogonal to each other and a λ / 4 plate. Have
The polarizing element is preferably disposed on the light source side of the λ / 4 plate.
According to the present invention, by inserting the polarizing element and the λ / 4 plate between the light source and the pulse dispersion compensator, only the ultrashort pulse laser beam directed to the pulse dispersion compensator is transmitted and returned to the light source. Since the light is blocked, the return light can be prevented from entering the light source.
Specifically, one linearly polarized light that has passed through the polarizing element passes through the λ / 4 plate in this order, is polarized into one circularly polarized light, and is emitted. The return light toward the light source is polarized to the other circularly polarized light by reflection and polarized to the other linearly polarized light when passing through the λ / 4 plate. The other linearly polarized light is prevented from entering the light source by the polarizing element.

In the above-mentioned invention, it is desirable that the incident prevention unit is configured by arranging the grating so as to be inclined with respect to the optical axis of the incident ultrashort pulse laser.
According to the present invention, since the incident preventing portion is configured to be inclined with respect to the optical axis of the ultrashort pulse laser incident on the grating, the diffracted light of the grating is coaxial with the optical axis. Therefore, it can be prevented that the light is emitted toward the light source. Therefore, return light (diffracted light) traveling from the pulse dispersion compensator to the light source can be prevented from entering the light source.

In the above invention, the incidence preventing section includes the grating, the optical axis of the ultrashort pulse laser emitted from the light source, and an intersection line between a plane substantially perpendicular to the grating and the plane of the grating It is desirable that it is configured so as to be rotatable around a rotation axis substantially parallel to the axis.
According to the present invention, the direction of the optical axis of return light (diffracted light) from the grating toward the light source can be changed by rotating and tilting the grating around the rotation axis. Therefore, return light (diffracted light) traveling from the pulse dispersion compensator to the light source can be prevented from entering the light source.

In the above invention, the incidence preventing unit rotates the grating substantially parallel to a line of intersection of a surface substantially perpendicular to the optical axis of the ultrashort pulse laser light incident on the grating and the surface of the grating. It is desirable to be configured by being arranged so as to be rotatable around an axis.
According to the present invention, the direction of the optical axis of return light (diffracted light) from the grating toward the light source can be changed by rotating and tilting the grating around the rotation axis. Therefore, return light (diffracted light) traveling from the pulse dispersion compensator to the light source can be prevented from entering the light source.

In the above invention, it is desirable that the incidence preventing portion is formed so that a plurality of grooves formed on the laser beam incident surface of the grating satisfy the following relational expression.
d <mλ / (2 sin α),
m = −2 or m = 2 (1)
Here, d is the groove interval of the grating, m is the order (integer), λ is the wavelength of the ultrashort pulse laser beam, and α is the angle of incidence of the ultrashort pulse laser beam on the grating.

  According to the present invention, since the number of grooves formed in the grating satisfies the relational expression (1), among many diffracted lights diffracted by the grating, diffracted light having orders of ± 2nd order or higher ( Return light) travels toward the light source and can be prevented from entering the light source.

  According to the ultrashort pulse laser transmission device of the present invention, since the incident prevention unit is provided, the return light from the pulse dispersion compensator to the light source can be blocked by the incident prevention unit and prevented from entering the light source. There is an effect.

[First Embodiment]
Hereinafter, a first embodiment of the ultrashort pulse laser transmission apparatus according to the present invention will be described with reference to FIG. Here, description will be made by applying the ultrashort pulse laser transmission device of the present invention to an example used for a multiphoton excitation scanning microscope.
FIG. 1 is an overall view illustrating a schematic configuration of an ultrashort pulse laser transmission device according to the present embodiment.
Note that the Z axis in FIG. 1 is an axis parallel to the emission optical axis of the ultrashort pulse laser beam, and the emission direction of the ultrashort pulse laser beam (the right direction in FIG. 1) is the positive direction. , The X axis is an axis that is included in the drawing and is perpendicular to the Z axis, the upper direction in FIG. 1 being the positive direction, and the Y axis is an axis perpendicular to the ZX plane. In this case, the front direction is the axis that becomes the positive direction.

  As shown in FIG. 1, the ultrashort pulse laser transmission device 1 includes an ultrashort pulse laser light source (light source) 3 that emits ultrashort pulse laser light, and an isolator (on the downstream side of the ultrashort pulse laser light source 3). (Incident prevention unit, rectifying element) 5, λ / 2 plate 7 disposed on the downstream side of the isolator 5, dispersion compensation optical system (pulse dispersion compensator) 9 disposed on the downstream side of the λ / 2 plate 7, , An optical axis adjustment optical system 11 disposed on the downstream side of the dispersion compensation optical system 9, and an output adjustment optical system 13 and a beam shaping optical system 15 disposed on the downstream side of the optical axis adjustment optical system 11. Has been. Further, a multiphoton microscope 17 to which the ultrashort pulse laser beam emitted from the ultrashort pulse laser transmission device 1 is guided is disposed.

As the ultrashort pulse laser light source 3, for example, a pulse laser oscillator that oscillates an S-polarized (one linearly polarized) ultrashort pulse laser beam having a wavelength of about 700 nm to 1000 nm can be used. A mode-locked titanium sapphire laser can be used.
The isolator 2 includes an optical element including a Faraday rotator (not shown) and a λ / 4 plate (not shown). Further, the isolator 2 polarizes the S-polarized light incident from the ultrashort pulse laser light source 3 side into the P-polarized light and emits it to the dispersion compensation optical system 9 side, and does not transmit the light incident from the dispersion compensation optical system 9 side. It is configured as follows.

The dispersion compensation optical system 9 includes a first grating (grating) 19 and a second grating (grating) 21 that are arranged substantially parallel to a plane obtained by rotating the YZ plane around the Y axis in the positive direction by a predetermined angle. It is roughly composed.
The first grating 19 is arranged so that the incident angle α of the ultrashort pulse laser beam emitted from the ultrashort pulse laser light source 3 is a predetermined angle, and the second grating 21 includes the first grating 19 and The second grating 21 is arranged to be movable in the vertical direction.
Further, the first grating 19 and the second grating 21 are placed in the S polarization arrangement.

The optical axis adjusting optical system 11 includes a first 45-degree total reflection mirror 23 disposed substantially parallel to a surface obtained by rotating the YZ plane about −45 ° around the Y-axis, and includes a first 45-degree total reflection. The mirror 23 is disposed so as to reflect light traveling in the + Z-axis direction in the −X-axis direction. The first 45-degree total reflection mirror 23 is arranged so as to be movable in the X-axis direction.
As the output adjustment optical system 13, an acousto-optic device such as AOTF (Acousto-Optic Tunable Filter) and AOM (Acousto-Optic Modulator), an electro-optic device, a linear polarizing plate with a rotation mechanism, and a light attenuation rate are controlled. An ND filter that can be used, a variable aperture that can control the aperture diameter, and the like can be used.
A beam expander, a spatial filter, or the like can be used for the beam shaping optical system 15.

Next, the operation of the ultrashort pulse laser transmission device 1 having the above configuration will be described.
First, for example, an S-polarized ultrashort pulse laser beam having a wavelength of about 700 nm to 1000 nm is emitted from the ultrashort pulse laser light source 3. The S-polarized ultrashort pulse laser light is polarized to P-polarized light by the isolator 5 and emitted toward the λ / 2 plate 7. The ultrashort pulse laser beam converted to P-polarized light is polarized to S-polarized light when passing through the λ / 2 plate 7 and is emitted toward the dispersion compensation optical system 9.

The S-polarized ultrashort pulse laser beam incident on the dispersion compensation optical system 9 is incident on the first grating 19. The ultrashort pulse laser beam incident on the first grating 19 is diffracted into many orders and emitted as a plurality of diffracted beams.
For example, when an ultrashort pulse laser beam having a wavelength of 700 nm is incident on the first grating 19 having an incident angle of −60 ° and a groove interval of 1.667 μm, the 0th order, the −1st order, the −2nd order, the −3rd order, -4th order diffracted light is generated.

When light having a wavelength of 720 nm is incident on the first grating 19, the angle formed between the -4th order diffracted light and the normal line of the first grating 19 among these diffracted lights, and an ultrashort pulse The incident angle α of the laser beam to the first grating 19 is close. Therefore, the fourth-order diffracted light becomes return light that is substantially coaxial with the optical axis of the incident ultrashort pulse laser light and travels in the direction of the ultrashort pulse laser light source 3.
Alternatively, when light having a wavelength of 960 nm is incident, the angle formed between the -3rd-order diffracted light and the normal line of the first grating 19 and the incident angle α of the ultrashort pulse laser light to the first grating 19 And get closer. Therefore, the -3rd order diffracted light becomes return light that is substantially coaxial with the optical axis of the incident ultrashort pulse laser beam and travels in the direction of the ultrashort pulse laser light source 3.

  The return light traveling in the direction of the ultrashort pulse laser light source 3 enters the λ / 2 plate 7, is polarized from S-polarized light to P-polarized light, and enters the isolator 5. Since the isolator 5 removes the P-polarized light incident from the dispersion compensation optical system 9 side without transmitting, the return light does not reach the ultrashort pulse laser light source 3.

Of the plurality of diffracted lights diffracted by the first grating 19, the −1st order diffracted light is incident on a second grating 21 arranged in parallel to the first grating 19.
The −1st order diffracted light incident on the second grating 21 is diffracted into many orders and emitted as a plurality of diffracted lights. The −1st order diffracted light diffracted by the second grating 21 travels in a direction parallel to the optical axis of the ultrashort pulse laser light incident on the first grating 19 to form a negative chirp. Moreover, the pulse width is extended by forming a negative chirp.

The laser light that is the −1st order diffracted light emitted from the second grating 21 is incident on the first 45-degree total reflection mirror 23 in the optical axis adjusting optical system 7 and reflected toward the −X axis direction. Is done.
The laser beam reflected by the first 45-degree total reflection mirror 23 enters the output adjustment optical system 13 and is adjusted to an appropriate output.
The laser light emitted from the output adjustment optical system 13 enters the beam shaping optical system 15 and is corrected to an appropriate beam diameter and beam divergence in the beam shaping optical system 15. Finally, the laser light emitted from the beam shaping optical system 15 is introduced into the multiphoton microscope 17.

  According to the above configuration, by inserting the isolator 5 between the ultrashort pulse laser light source 3 and the dispersion compensation optical system 9, only the ultrashort pulse laser beam directed to the dispersion compensation optical system 9 is transmitted. Since the return light toward the short pulse laser light source 3 is blocked, the return light can be prevented from entering the ultrashort pulse laser light source 3.

  By forming laser light having negative chirp by the dispersion compensation optical system 9, positive chirp generated when the pulse laser light passes through the medium of the output adjustment optical system 13, the beam shaping optical system 15, and the multiphoton microscope 17 is generated. Can be corrected. For this reason, the pulse width of the pulse laser beam expanded by the dispersion compensation optical system 4 is compressed by positive chirp, and becomes an ultrashort pulse laser beam when reaching the specimen of the multiphoton microscope 17.

When the second grating 21 of the dispersion compensation optical system 9 is translated in a direction substantially perpendicular to the light incident surface, the optical path length between the first grating 19 and the second grating 21 is changed, The amount of negative chirp of the pulse laser beam emitted from the dispersion compensation optical system 9 is changed.
Therefore, by controlling the position of the second grating 21, it is possible to control the amount of negative chirp of the pulse laser beam by the dispersion compensation optical system 9.

As described above, when the second grating 21 is translated in the substantially vertical direction, the −1st order diffracted light emitted from the second grating 21 also moves in the X-axis direction.
At the same time, the first 45-degree total reflection mirror 23 of the optical axis adjusting optical system 11 is moved in the X-axis direction in accordance with the movement of the −1st order diffracted light. The light is always incident on a predetermined position of the first 45-degree total reflection mirror 23 and reflected in the −X axis direction. As a result, the displacement of the optical axis of the laser beam emitted from the dispersion compensation optical system 9 can be corrected, and the optical axis of the pulse laser beam emitted from the optical axis adjustment optical system 11 can always be kept coaxial.

Further, as described above, not only when the optical path length between the first grating 5 and the second grating 6 is changed, but also when the wavelength of the laser light emitted from the ultrashort pulse laser light source 3 is changed. However, since the direction in which the −1st-order diffracted light is emitted changes, the optical axis of the laser light emitted from the dispersion compensation optical system 9 is displaced in the X-axis direction.
Even in such a case, the optical axis of the pulse laser beam emitted from the optical axis adjusting optical system 11 can always be kept coaxial.

As described above, the λ / 2 plate 7 is disposed between the isolator 5 and the dispersion compensation optical system 9, and the P-polarized light emitted from the isolator 5 is polarized into S-polarized light by the λ / 2 plate 7. Alternatively, P-polarized light may be converted to S-polarized light by arranging two 45-degree total reflection mirrors instead of the λ / 2 plate 7.
Alternatively, without using the λ / 2 plate 7 or the 45-degree total reflection mirror, the P-polarized light emitted from the isolator 5 and the first grating 19 placed in the P-polarization arrangement as it is, The light may be incident on the second grating 21.

  Further, as described above, the λ / 2 plate 7 may be disposed in the optical path between the isolator 2 and the first grating 5, or the λ / 2 plate 7 is disposed between the ultrashort pulse laser light source 3 and the isolator 5. The isolator 5 may be rotated 90 degrees around the optical path axis. By arranging in this way, the light emitted from the isolator 5 becomes S-polarized light and can be directly incident on the first grating 19 having the S-polarized arrangement.

[Second Embodiment]
Next, a second embodiment of the present invention will be described with reference to FIG.
FIG. 2 is an overall view illustrating a schematic configuration of the ultrashort pulse laser transmission device according to the present embodiment.
The basic configuration of the ultrashort pulse laser transmission device of this embodiment is the same as that of the first embodiment, but the first embodiment is arranged between the ultrashort pulse laser light source and the dispersion compensation optical system. The components are different. Therefore, in the present embodiment, only the components arranged between the ultrashort pulse laser light source and the dispersion compensation optical system will be described, and the same components as those in the first embodiment will be denoted by the same reference numerals. Therefore, the description is omitted.

  As shown in FIG. 2, the ultrashort pulse laser transmission device 51 includes an ultrashort pulse laser light source 3 that emits an ultrashort pulse laser beam, and a polarization beam splitter (incident on the downstream side of the ultrashort pulse laser light source 3). Prevention unit, polarizing element) 55, a λ / 4 plate (incident prevention unit) 57 disposed downstream of the polarization beam splitter 55, and a dispersion compensation optical system 9 disposed downstream of the λ / 4 plate 57. , An optical axis adjustment optical system 11 disposed on the downstream side of the dispersion compensation optical system 9, and an output adjustment optical system 13 and a beam shaping optical system 15 disposed on the downstream side of the optical axis adjustment optical system 11. Has been. In addition, a multiphoton microscope 17 to which an ultrashort pulse laser beam emitted from the ultrashort pulse laser transmission device 51 is guided is arranged.

The polarization beam splitter 55 includes a polarization reflection surface 56 that transmits S-polarized light and reflects P-polarized light. The polarization reflection surface 56 is a surface obtained by rotating the YZ plane by −45 degrees around the Y axis. Are arranged substantially in parallel. Therefore, when the P-polarized light traveling in the −Z-axis direction enters the polarization beam splitter 55, it is reflected by the polarization reflection surface 56 toward the + X-axis direction.
Instead of the polarizing beam splitter 55, an element such as a polarizing filter or an acousto-optic element may be used.

Next, the operation of the ultrashort pulse laser transmission device 51 having the above configuration will be described.
First, the S-polarized ultrashort pulse laser beam emitted from the ultrashort pulse laser light source 3 enters the polarization beam splitter 55. The S-polarized ultrashort pulse laser light passes through the polarization beam splitter 55 as it is and is emitted toward the λ / 4 plate 57. The S-polarized light incident on the λ / 4 plate 57 is polarized into one direction circularly polarized light, for example, clockwise circularly polarized light, and is emitted toward the dispersion compensation optical system 9.

The clockwise circularly polarized ultrashort pulse laser light incident on the dispersion compensation optical system 9 is incident on the first grating 19. The ultrashort pulse laser beam incident on the first grating 19 is diffracted into many orders and emitted as a plurality of diffracted beams.
Among them, the diffracted light of a predetermined order becomes return light that is substantially coaxial with the optical axis of the incident ultrashort pulse laser light and travels in the direction of the ultrashort pulse laser light source 3 under the condition of laser light of a predetermined wavelength.

When the return light traveling in the direction of the ultrashort pulse laser light source 3 is diffracted by the first grating 19, it becomes circularly polarized light in the other direction, for example, counterclockwise circularly polarized light. The return light, which is counterclockwise circularly polarized light, enters the λ / 4 plate 57, is polarized to P-polarized light, and is emitted toward the polarizing beam splitter 55.
The return light polarized to P-polarized light is incident on the polarization beam splitter 55, reflected in the + X-axis direction by the polarization reflection surface 56, and removed from the outgoing optical axis of the ultrashort pulse laser light source 3.
Since the subsequent operation of the optical system downstream of the dispersion compensation optical system 9 is the same as that of the first embodiment (see FIG. 1), its configuration is shown in FIG.

  According to the above configuration, by inserting the polarization beam splitter 55 and the λ / 4 plate 57 between the light source and the dispersion compensation optical system 9, only the ultrashort pulse laser beam directed to the dispersion compensation optical system 9 is transmitted. In addition, since the return light toward the ultrashort pulse laser light source 3 is blocked, the return light can be prevented from entering the ultrashort pulse laser light source 3.

  As described above, the polarization beam splitter 55 may be disposed between the ultrashort pulse laser light source 3 and the λ / 4 plate 57 to remove the P-polarized light, or instead of the polarization beam splitter 55 being disposed, An optical system for removing light other than S-polarized light (for example, P-polarized light) may be disposed inside the ultrashort pulse laser light source 3.

[Third Embodiment]
Next, a third embodiment of the present invention will be described with reference to FIGS.
FIG. 3 is an overall plan view illustrating a schematic configuration of the ultrashort pulse laser transmission device according to the present embodiment. 4 is a side view illustrating the configuration of the optical axis adjustment optical system of FIG. 3, and FIG. 5 is a front view illustrating the configuration of the optical axis adjustment optical system of FIG.
The basic configuration of the ultrashort pulse laser transmission device of this embodiment is the same as that of the first embodiment, but is different from the first embodiment between the ultrashort pulse laser light source and the output adjustment optical system. The components are different. Therefore, in the present embodiment, only components disposed between the ultrashort pulse laser light source and the output adjustment optical system will be described using FIGS. 3 to 5, and the same components as those in the first embodiment will be described. Are denoted by the same reference numerals, and the description thereof is omitted.

  As shown in FIG. 3, the ultrashort pulse laser transmission device 101 includes an ultrashort pulse laser light source 3 that emits an ultrashort pulse laser beam, and a dispersion compensation optical system (on the downstream side of the ultrashort pulse laser light source 3). (Pulse dispersion compensator) 109, an optical axis adjusting optical system 111 disposed on the downstream side of the dispersion compensating optical system 109, an output adjusting optical system 13 disposed on the downstream side of the optical axis adjusting optical system 111, and beam shaping optics. The system 15 is schematically configured. Further, a multiphoton microscope 17 to which the ultrashort pulse laser beam emitted from the ultrashort pulse laser transmission device 101 is guided is arranged.

The dispersion compensation optical system 109 is generally configured by a first grating (grating) 119 and a second grating (grating) 121 disposed substantially parallel to the first grating 19.
The first grating 119 and the second grating 121 have a rotation axis P1 that is a plane obtained by rotating the YZ plane by a predetermined angle around the Y axis in a positive direction and substantially parallel to the intersection line of the plane and the ZX plane. It is arranged substantially parallel to a plane rotated around a predetermined angle.

On the laser light incident surfaces (diffraction surfaces) of the first grating 119 and the second grating 121, grooves 120 extending in a direction substantially perpendicular to the Z axis are formed.
In other words, the first grating 119 and the second grating 121 are arranged substantially parallel to a plane obtained by rotating the YZ plane by a predetermined angle around the Y axis in the positive direction (first and second). (Arrangement state in the embodiment) is arranged in a state of being rotated by a predetermined angle around the rotation axis P1 substantially perpendicular to the groove 120.

  Similarly to the second grating 21 of the first and second embodiments, the second grating 121 is disposed so as to be movable in a direction substantially perpendicular to the light incident surface, and the second grating 121 is arranged. The amount of negative chirp formation of the pulse laser beam by the dispersion compensation optical system 109 is controlled by the parallel movement of.

As shown in FIGS. 3 to 5, the optical axis adjusting optical system 111 includes a first 45-degree total reflection mirror 123, a second 45-degree total reflection mirror 125, and a third 45-degree total reflection mirror 127. It is roughly composed.
The first 45-degree total reflection mirror 123 is arranged so as to be substantially parallel to a plane obtained by rotating the XY plane around the Y axis by +45 degrees and reflects light traveling in the + Z-axis direction in the -X-axis direction. The total reflection mirror. The first 45-degree total reflection mirror 123 is arranged so as to be movable in the X-axis direction.
The second 45-degree total reflection mirror 125 is disposed so as to be substantially parallel to a plane obtained by rotating the YZ plane about +45 degrees around the Z axis, and disposed so as to reflect light traveling in the −X axis direction in the + Y axis direction. The total reflection mirror. The second 45-degree total reflection mirror 125 is arranged so as to be movable in the X-axis direction.
The third 45-degree total reflection mirror 127 is disposed substantially parallel to a plane obtained by rotating the XY plane by +45 degrees around the X axis, and is disposed so as to reflect light traveling in the + Y axis direction in the + Z axis direction. It is a total reflection mirror.

Next, the operation of the ultrashort pulse laser transmission device 101 having the above configuration will be described.
First, the S-polarized ultrashort pulse laser beam emitted from the ultrashort pulse laser light source 3 enters the first grating 119 of the dispersion compensation optical system 109. Since the first grating 119 is disposed in a tilted state rotated by a predetermined angle around the rotation axis P1, the optical axis of each order of diffracted light emitted from the first grating 119 is in the ZX plane. The plane is parallel and deviates from the plane including the optical axis of the ultrashort pulse laser beam incident on the first grating 119.
That is, each order of diffracted light is emitted from the first grating 119 in a direction intersecting the ZX plane at a predetermined angle. In the present embodiment, description will be made by applying to an example in which each order of diffracted light is emitted in the + Y-axis direction.
Therefore, any diffracted light of each order does not travel substantially parallel to the Z axis and in the −Z axis direction, and can be prevented from entering the ultrashort pulse laser light source 3.

For example, the present embodiment will be described by applying it to the case where the exit diameter of the ultrashort pulse laser light source 3 is 5 mm and the optical path length between the ultrashort pulse laser light source 3 and the first grating 119 is 1 meter. If the optical axis of the return light from the first grating 119 has an intersection angle of 0.14 ° or more with respect to the output optical axis of the ultrashort pulse laser light source 3, the return light is an ultrashort pulse laser. It does not enter the exit of the light source 3.
Therefore, in such a case, the first grating 119 has a diffraction angle of the diffracted light of orders other than the −1 order (diffracted light to be returned light) of 0.14 with respect to the emission optical axis of the ultrashort pulse laser light source 3. It is rotationally arranged around the rotation axis P1 so as to have a crossing angle of not less than °.
In addition, these values are not limited to the above-mentioned values, and can take different values depending on individual embodiments.

Of the many orders of light diffracted by the first grating 119, the −1st order diffracted light is incident on the second grating 121 and further diffracted by the second grating 121.
Of the diffracted light of the second grating 121, the −1st order diffracted light travels in a direction parallel to the optical axis of the laser light incident on the first grating 119 (a direction parallel to the Z axis), and the optical axis adjusting optical system. 111 is incident.

  As shown in FIGS. 3 and 5, the laser light incident on the optical axis adjusting optical system 111 is incident on the first 45-degree total reflection mirror 123, reflected toward the −X axis direction, and the second 45. Is incident on the total reflection mirror 125. As shown in FIGS. 4 and 5, the laser light incident on the second 45-degree total reflection mirror 125 is reflected toward the + Y-axis direction and is incident on the third 45-degree total reflection mirror 10. As shown in FIGS. 3 and 4, the laser light incident on the third 45-degree total reflection mirror 10 is reflected toward the + Z-axis direction and emitted toward the output adjustment optical system 13.

  Here, in order to control (change) the formation amount of the negative chirp of the pulse laser beam, when the second grating 121 is translated in a direction away from the first grating 119, for example, FIGS. As indicated by the dotted line in the middle, the optical axis of the −1st order diffracted light emitted from the second grating 121 translates in the + X axis direction and translates in the + Y axis direction.

  In such a case, the first 45-degree total reflection mirror 123 is moved in the + X-axis direction according to the movement amount of the second grating 121 as shown in FIGS. 3 and 5, and the optical axis of the diffracted light Of the laser beam emitted from the first 45-degree total reflection mirror 123 in the −X-axis direction is prevented from moving in the Z-axis direction.

  As shown in FIGS. 4 and 5, the optical axis of the laser light incident on the second 45-degree total reflection mirror 125 is in the + Y-axis direction due to the parallel movement of the optical axis of the diffracted light in the + Y-axis direction. It is translated to. The second 45-degree total reflection mirror 125 is moved in the + X-axis direction according to the movement amount of the second grating 121, and the parallel movement of the optical axis of the diffracted light in the + Y-axis direction is absorbed. 2, the parallel movement of the optical axis of the laser beam emitted from the 45-degree total reflection mirror 125 in the + Y-axis direction in the X-axis direction is prevented.

  Since the subsequent operation of the optical system downstream of the optical axis adjusting optical system 111 is the same as that of the first embodiment (see FIG. 1), the configuration is shown in FIGS. 3 and 4 and the description thereof is omitted. .

  According to the above configuration, the first grating 119 and the second grating 121 are rotated around the rotation axis P1 and tilted to return light (diffracted light) from the first grating 119 toward the ultrashort pulse laser light source 3. ) Direction of the optical axis can be changed. Therefore, return light (diffracted light) traveling from the dispersion compensation optical system 109 toward the ultrashort pulse laser light source 3 can be prevented from entering the ultrashort pulse laser light source 3.

  Note that, as described above, the first grating 119 and the second grating 121 may be individually rotated and arranged around the rotation axis P1, or the first grating 119 and the second grating 121 may be arranged. May be rotated and tilted around the rotation axis P1, and the same effect can be obtained.

  As described above, the optical axis adjusting optical system 111 may be composed of three 45-degree total reflection mirrors 123, 125, 127, or may be composed of two total reflection mirrors. An optical element may be used. Any optical system that absorbs the movement of the laser beam emitted from the dispersion compensation optical system 109 and can emit the laser beam toward a predetermined position of the multiphoton microscope 17 is not particularly limited.

[Fourth Embodiment]
Next, a fourth embodiment of the present invention will be described with reference to FIG.
FIG. 6 is an overall plan view illustrating a schematic configuration of the ultrashort pulse laser transmission device according to the present embodiment.
The basic configuration of the ultrashort pulse laser transmission device of this embodiment is the same as that of the first embodiment, but is different from the first embodiment between the ultrashort pulse laser light source and the output adjustment optical system. The components are different. Therefore, in the present embodiment, only the components arranged between the ultrashort pulse laser light source and the output adjustment optical system will be described with reference to FIG. 6, and the same components as those in the first embodiment are The same reference numerals are given and description thereof is omitted.

  As shown in FIG. 6, the ultrashort pulse laser transmission device 151 includes an ultrashort pulse laser light source 3 that emits an ultrashort pulse laser beam, and a dispersion compensation optical system (on the downstream side of the ultrashort pulse laser light source 3 ( (Pulse dispersion compensator) 159, the optical axis adjusting optical system 11 disposed on the downstream side of the dispersion compensating optical system 159, the output adjusting optical system 13 and the beam shaping optics disposed on the downstream side of the optical axis adjusting optical system 11. The system 15 is schematically configured. Further, a multiphoton microscope 17 to which the ultrashort pulse laser beam emitted from the ultrashort pulse laser transmission device 151 is guided is arranged.

The dispersion compensation optical system 159 is generally configured by a first grating (grating) 169 and a second grating (grating) 171 arranged in parallel to the first grating 19.
The first grating 169 and the second grating 171 are arranged in parallel to a plane obtained by rotating the YZ plane by a predetermined angle around the Y axis in the positive direction, and are parallel to the Y axis. The second grating 171 is disposed so as to be rotatable around a rotation axis P2 passing through the center of the second grating 171.

Next, the operation of the ultrashort pulse laser transmission device 151 having the above configuration will be described.
First, an S-polarized ultrashort pulse laser beam emitted from the ultrashort pulse laser light source 3 enters the first grating 169 of the dispersion compensation optical system 159. The laser light incident on the first grating 169 is diffracted into many orders, and the −1st order diffracted light among them is arranged to be inclined so as to be parallel to the diffraction surface of the first grating 169. Is incident on the grating 171.
The laser light incident on the second grating 171 is further diffracted, and the −1st order diffracted light of the plurality of diffracted lights is parallel to the optical axis of the laser light incident on the first grating 169 (Z-axis). In the direction parallel to the optical axis) and enters the optical axis adjusting optical system 11.

Since the subsequent operation of the optical system downstream from the dispersion compensation optical system 159 is the same as that of the first embodiment (see FIG. 1), the configuration is shown in FIG.

  Here, when the condition described later is satisfied, the diffracted light of a predetermined order among the other orders of diffracted light travels in the −Z direction substantially coaxially with the outgoing optical axis of the ultrashort pulse laser light source 3, and thus the first The grating 169 is rotated and tilted about the rotation axis P <b> 2 to shift the optical axis of the diffracted light of the predetermined order from the emission optical axis of the ultrashort pulse laser light source 3.

At this time, the incident angle of the −1st order diffracted light that enters the second grating 171 from the first grating 169 also changes. Therefore, the second grating 171 is also rotated and tilted around the rotation axis P2 at the same time, and the optical axis of the −1st order diffracted light emitted from the second grating 171 is kept substantially parallel to the Z axis.
The −1st order diffracted light emitted from the second grating 171 is kept substantially parallel to the Z axis, but moves in parallel in the X axis direction. Therefore, as in the first embodiment, the movement of the optical axis is corrected by moving the first 45-degree total reflection mirror 23 in the X-axis direction.

The condition that the diffracted light of the predetermined order advances in the −Z direction substantially coaxially with the outgoing optical axis of the ultrashort pulse laser light source 3 is a condition in which the following parameters satisfy the relational expression (2).
λ = (2d · sin α) / m (2)
Where d is the groove interval of the first grating 169, m is the order (integer) of the diffracted light, λ is the wavelength of the laser light incident on the grating 169, and α is the incident angle of the laser light incident on the first grating 169. It is.

  Further, since the wavelength λ of the ultrashort pulse laser beam emitted from the ultrashort pulse laser light source 3 is changed according to a measurement request by the multiphoton microscope 17, each parameter described above is changed each time the wavelength λ is changed. It is confirmed whether the relational expression (2) is satisfied.

  According to the above configuration, the direction of the optical axis of the return light (diffracted light) from the first grating 169 toward the ultrashort pulse laser light source 3 is changed by rotating and tilting the first grating 169 about the rotation axis P2. It can be changed. Therefore, return light (diffracted light) traveling from the dispersion compensation optical system 159 toward the ultrashort pulse laser light source 3 can be prevented from entering the ultrashort pulse laser light source 3.

  As described above, the first grating 169 and the second grating 171 may be individually arranged so as to be rotatable around the rotation axis P2. Alternatively, the first grating 169 and the second grating 171 may be arranged. May be arranged as a unit so as to be rotatable around the rotation axis P2 of the first grating 169, and the same effect can be obtained.

[Fifth Embodiment]
Next, a fifth embodiment of the present invention will be described with reference to FIG.
FIG. 7 is an overall plan view illustrating a schematic configuration of the ultrashort pulse laser transmission device according to the present embodiment.
The basic configuration of the ultrashort pulse laser transmission device of the present embodiment is the same as that of the first embodiment, but the first embodiment is arranged between the ultrashort pulse laser light source and the optical axis adjusting optical system. Different components are used. Therefore, in the present embodiment, only the components arranged between the ultrashort pulse laser light source and the optical axis adjusting optical system will be described with reference to FIG. 7, and the same components as those in the first embodiment will be described. The same reference numerals are given and the description thereof is omitted.

  As shown in FIG. 7, the ultrashort pulse laser transmission device 201 includes an ultrashort pulse laser light source 3 that emits ultrashort pulse laser light, and a dispersion compensation optical system (on the downstream side of the ultrashort pulse laser light source 3). A pulse dispersion compensator) 209, an optical axis adjusting optical system 11 disposed downstream of the dispersion compensating optical system 209, an output adjusting optical system 13 and beam shaping optics disposed downstream of the optical axis adjusting optical system 11. The system 15 is schematically configured.

  The dispersion compensation optical system 209 is generally configured by a first grating (grating) 219 and a second grating (grating) 221 arranged in parallel to the first grating 219. The second grating 221 is arranged in parallel with a plane obtained by rotating the YZ plane by a predetermined angle around the Y axis in the positive direction.

Further, the number of grooves (not shown) satisfying the following relational expression is formed on the laser light incident surfaces of the first grating 219 and the second grating 221.
d <mλ / (2 sin α) m = −2 or m = 2 (1)
Where d is the groove spacing of the gratings 219 and 221, m is the order (integer) of the diffracted light, λ is the wavelength of the laser light incident on the gratings 219 and 221, and α is the incident angle of the laser light incident on the gratings 219 and 221. It is.

Next, the operation of the ultrashort pulse laser transmission device 201 having the above configuration will be described.
First, the S-polarized ultrashort pulse laser beam emitted from the ultrashort pulse laser light source 3 is incident on the first grating 219 of the dispersion compensation optical system 209. The laser light incident on the first grating 219 is diffracted into many orders, and the −1st order diffracted light is emitted toward the second grating 221.
The laser light incident on the second grating 221 is further diffracted, and the −1st order diffracted light of the plurality of diffracted lights is parallel to the optical axis of the laser light incident on the first grating 219 (Z-axis). In the direction parallel to the optical axis) and enters the optical axis adjusting optical system 11.

  Of the many diffracted lights diffracted by the first grating 219, the number of grooves formed in the first grating 219 satisfies the relational expression (1) in the diffracted lights having orders of ± 2nd order or higher. Therefore, it is possible to prevent the light from traveling in the −Z direction substantially coaxially with the output optical axis of the ultrashort pulse laser light source 3.

  For example, when the wavelength of the ultrashort pulse laser beam emitted from the ultrashort pulse laser light source 3 is 700 nm and the incident angle to the first grating 219 is −60 °, the relational expression (1) is obtained. The groove interval d to be filled is calculated as 0.808 μm.

  According to the above configuration, since the number of grooves formed in the first grating 219 satisfies the relational expression (1), among the many diffracted lights diffracted by the first grating 219, ± 2 It is possible to prevent the diffracted light (return light) having the order of the order or higher from traveling toward the ultrashort pulse laser light source 3 and entering the ultrashort pulse laser light source 3.

As described above, as the ultrashort pulse laser transmission device 201, the ultrashort pulse laser light source 3, the dispersion compensation optical system 209, the optical axis adjustment optical system 11, the output adjustment optical system 13, the beam shaping optical system 15, and the multiphoton. It may be configured only by the microscope 17, or an optical system that generates a positive chirp may be disposed in the optical path between the ultrashort pulse laser light source 3 and the multiphoton microscope 17.
By arranging the optical system, for example, the negative chirp by the first grating 219 and the second grating 221 having the number of grooves satisfying the relational expression (1) is changed to the positive chirp on the sample surface in the multiphoton microscope 13. If the compensation is too much more than removing the compensation, the compensation amount can be adjusted by the optical system. Examples of the optical system include optical elements such as glass materials, plastic materials, and semiconductor crystals, acousto-optic elements, electro-optic elements, optical devices such as single-mode fibers, pulse dispersion compensators including grating pairs, and prism pairs. .

The technical scope of the present invention is not limited to the above embodiment, and various modifications can be made without departing from the spirit of the present invention.
For example, in the above-described embodiment, the description has been made by applying to the embodiment in which the negative chirp is formed by diffracting the laser light twice by using two gratings as the dispersion compensation optical system. Without being limited to the dispersion compensation optical system used, a dispersion compensation optical system that forms a negative chirp by diffracting laser light twice using one grating and two total reflection mirrors, or one grating and a total reflection mirror The present invention can also be applied to a dispersion compensation optical system that forms negative chirp by diffracting a laser four times using four sheets, two gratings and one total reflection mirror, or four gratings.
Further, the dispersion compensation optical system can be applied to a combination of a grating pair and a prism pair.

1 is an overall view illustrating a schematic configuration of a first embodiment of an ultrashort pulse laser transmission device according to the present invention. It is a whole figure explaining 2nd Embodiment schematic structure of the ultrashort pulse laser transmission apparatus which concerns on this invention. FIG. 5 is an overall view illustrating a schematic configuration of a third embodiment of an ultrashort pulse laser transmission device according to the present invention. It is a side view explaining the structure of the optical axis adjustment optical system of FIG. It is a front view explaining the structure of the optical axis adjustment optical system of FIG. FIG. 9 is an overall view illustrating a schematic configuration of a fourth embodiment of an ultrashort pulse laser transmission device according to the present invention. FIG. 9 is an overall view illustrating a schematic configuration of a fifth embodiment of an ultrashort pulse laser transmission device according to the present invention.

Explanation of symbols

1, 51, 101, 151, 201 Ultrashort pulse laser transmission device 3 Ultrashort pulse laser light source (light source)
5 Isolator (incident prevention part, rectifier)
9, 109, 159, 209 Dispersion compensation optical system (pulse dispersion compensator)
19, 119, 169, 219 First grating (grating)
21, 121, 171, 221 Second grating (grating)
55 Polarizing beam splitter (incident prevention part, polarizing element)
57 λ / 4 plate (incident prevention part)
P1, P2 rotary shaft

Claims (3)

A light source that emits ultrashort pulse laser light;
A pulse dispersion compensator comprising a grating that receives the ultrashort pulse laser light and separates the ultrashort pulse laser light in a plane perpendicular to the longitudinal direction of the groove;
An incident prevention unit that tilts the grating around an axis orthogonal to the plane and prevents return light from the pulse dispersion compensator from traveling toward the light source from entering the light source ;
The pulse dispersion compensator is
A first grating disposed on the laser light source side;
A pair of gratings consisting of a second grating disposed opposite the first grating;
The second grating is adjusted to be parallel to the first grating whose rotation angle is adjusted when the wavelength is tunable,
An optical axis adjusting optical system that keeps the optical axis emitted from the pulse dispersion compensator coaxial with the movement of the -1st order or 1st order diffracted light emitted from the second grating;
The optical axis adjusting optical system is
Total reflection means provided separately from the first grating and the second grating;
An ultrashort pulse laser transmission device comprising: moving means for moving the total reflection means in accordance with movement of −1st order or 1st order diffracted light emitted from the second grating . 2. The ultrashort pulse laser transmission device according to claim 1, wherein the incident prevention unit inclines the grating so that an interval between grooves formed on the laser light incident surface of the grating satisfies the following relational expression.
d <mλ / (2 sin α),
m = -2, or m = 2 (1)
Here, d is the groove interval of the grating, m is the order (integer), λ is the wavelength of the ultrashort pulse laser beam, and α is the angle of incidence of the ultrashort pulse laser beam on the grating. 2. The ultrashort pulse laser transmission according to claim 1, wherein the incident prevention unit tilts the grating so that the wavelength of the ultrashort pulse laser beam does not satisfy the following condition when the wavelength of the ultrashort pulse laser beam is variable. apparatus.
λ = (2d · sin α) / m (2)
Here, d is the groove interval of the grating, m is the order (integer), λ is the wavelength of the ultrashort pulse laser beam, and α is the angle of incidence of the ultrashort pulse laser beam on the grating.

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