CN102759402B - Rotary Fourier transform interference imaging spectrometer - Google Patents

Abstract

The invention discloses a rotary Fourier transform interference imaging spectrometer, which comprises a pre-collimation objective lens, a cube-corner reflector, a beam splitter, a rear imaging objective lens, a detector and a control and processing module, which can reduce target light energy Therefore, it has the characteristics of high luminous flux and high detection sensitivity; the traditional linear motion scanning method of moving mirror is replaced by the rotating scanning method of beam splitter or cube-corner mirror, which avoids a series of problems caused by the precision linear scanning moving mirror. Technical difficulties; the use of a transverse shear interferometer based on the Michelson interference principle has the characteristics of a common optical path, even if the beam splitter shakes slightly during rotation, the interference effect will not be affected; the cube-corner mirror replaces the traditional The plane mirror in the Fourier transform imaging spectrometer avoids the problems caused by the tilt of the plane mirror. All of these have improved the stability, reliability and shock resistance of the instrument, and made the structure of the invention more compact.

Description

A Rotary Fourier Transform Interferometric Imaging Spectrometer

technical field

The invention relates to the field of spectral imaging, in particular to a high-throughput and high-stability rotary Fourier transform interference imaging spectrometer.

Background technique

Compared with traditional dispersive imaging spectrometers, Fourier transform imaging spectrometers have the characteristics of high luminous flux, high spectral resolution, and high signal-to-noise ratio. It expands the field of spectral research, has received widespread attention from all over the world, and has developed rapidly. It is widely used in the fields of physical evidence identification, agricultural production, resource exploration, environmental monitoring, disaster prevention and mitigation, material identification, and public safety.

The Fourier transform spectrometer based on time modulation has higher spectral resolution and sensitivity, but it requires high stability of the measurement platform. In order to achieve high-precision spectral image measurement, a high-stable structure and high-precision mechanical scanning mechanism are required. Time-modulated Fourier transform spectrometers are mostly based on Michelson interferometers. Its outstanding point is its high sensitivity, which relies on the movement of the moving mirror to generate a large optical path difference, thereby achieving high spectral resolution detection. However, the tilt and lateral movement of the moving mirror during scanning This makes the system very sensitive to disturbances of mechanical vibration. Therefore, an additional servo system is required to control the moving mirror. This makes the spectrometer system complex and susceptible to temperature, thereby limiting the range of applications of the spectrometer. The precise moving mirror mechanism that uses rotating mirror instead of linear motion or swing has high system stability, detection sensitivity and detection speed.

Bennett et al. proposed a time-modulated Fourier transform imaging spectrometer based on Michelson interferometer (Imaging Fourier transform spectrometer.Proc.SPIE 1993,1937:191-200) in 1993. The performance requirements are extremely high, and the environment and temperature have a great influence on it.

In 1997, Wadsworth et al proposed a rotating mirror interference spectroscopy technology solution (Ultra high speed chemical imaging spectrometer. Proc SPIE, 1997, 3082: 148-154). In this solution, the optical path difference generated by the rotation of the rotating mirror will be nonlinear due to the difference in the refractive index of different wavelengths, thus putting forward high requirements for the selection of the material of the rotating mirror.

In 1999, Griffiths et al proposed the principle of reflective high-speed rotating mirror infrared interference spectrometer (Ultrarapid scanning Fourier transform infrared spectrometry. Vibrational Spectroscopy, 1999, 19(1): 165-176). It can only sample a single pixel. If you want to obtain the interferogram of a line target or a surface target, you must scan point by point, and you cannot directly obtain an image with a unified map. This kind of spectrometer system has poor real-time performance, low resolution, small luminous flux entering the system, and narrow applicable working range.

Chinese patent 102322956A and Yuan Yan et al. (design method of ROSI for high-sensitivity interferometric spectroscopic imager ROSI, Acta Photonica Sinica, 2007, 36(2):279-281) are all based on sagnac beam splitting structure of rotating mirror interference imaging spectroscopy. The two spectrometers using this principle cannot make the sagnac structure into a solid body, the angle between the beam splitter and the two mirrors is strictly limited, it is difficult to install and adjust, the structure is not compact, and the stability is poor.

To sum up, so far, the linear moving mirror scanning and rotating mirror scanning principles of time-modulated Fourier transform spectrometers have their own characteristics, but they all have poor stability, high requirements for rotating mirror materials, and images that cannot be directly obtained. , and low luminous flux, difficult to install and adjust, not compact structure and other problems.

Contents of the invention

In view of this, the present invention provides a rotary Fourier transform interference imaging spectrometer, which can perform interference spectrum imaging of a target with high luminous flux and high stability.

A rotary Fourier transform interference imaging spectrometer of the present invention includes a pre-collimation objective lens, a cube-corner mirror, a beam splitter, a rear imaging objective lens, a detector, and a control and processing module, wherein,

The front collimating objective lens is placed in front of the target to convert the radiation beam of the target into a parallel beam, the beam splitter is placed in the optical path behind the front collimating objective lens, and the beam splitter and the parallel beam form an angle of 45°;

There are two corner cube mirrors, which are respectively defined as a first corner cube mirror and a second corner cube mirror, wherein the first corner cube mirror is placed in the reflection light path of the beam splitter, and the first corner corner cube reflector The diagonal of the mirror passes through the center of symmetry of the beamsplitter and is at a 45° angle to the beamsplitter; the second cube-corner mirror is located in the transmitted beam path of the beamsplitter, the second cube-corner mirror The mirrors are distributed symmetrically with respect to the beam splitter; the first cube-corner mirror and the second cube-corner mirror form a cube-corner mirror group;

The beam splitter and the cube-corner mirror group rotate relatively with the symmetrical center of the beam splitter as the center point, so as to change the optical path difference of the two beams transmitted and refracted from the beam splitter;

The post-imaging objective lens is a Fourier transform lens, which is placed in the optical path of the beam splitter on the side opposite to the first cube mirror, and is used for interferometric imaging of the two beams transmitted and refracted from the beam splitter;

The detector is placed on the focal plane of the rear imaging objective lens for receiving the image plane interference pattern formed on the focal plane;

The control and processing module is connected to the detector, on the one hand controls the sampling frequency of the detector so that the sampling frequency q relationship of the detector satisfies: Where ω is the relative rotation speed between the beam splitter and the cube-corner mirror group, s is the size of the detector pixel, f′ is the focal length of the post-imaging objective lens, and α is the relative rotation speed between the beam splitter and the cube-corner mirror group Turned angle; on the other hand, the control and processing module stores and processes the image plane interferogram received by the detector, so as to obtain the spectral data cube of the target;

A rotary Fourier transform interference imaging spectrometer of the present invention also includes a rotation and translation device, which is used to drive the entire interference imaging spectrometer to rotate, thereby changing the scanning window of the imaging device.

A rotary Fourier transform interference imaging spectrometer of the present invention also includes a swing mirror placed in front of the front collimation objective lens, the swing mirror reflects the target radiation beam onto the front collimation objective lens, and changes The optical system enters the pupil field of view, thereby changing the scanning window of the imaging device.

The front collimating objective lens is composed of two off-axis parabolic reflectors, which are respectively defined as a first off-axis parabolic reflector and a second off-axis parabolic reflector, wherein the object focus of the second off-axis parabolic reflector is the same as that of the first off-axis parabolic reflector. The image planes of an off-axis parabolic reflector coincide with each other; the first off-axis parabolic reflector reflects the beam of target radiation to the second off-axis parabolic reflector, collimates it, and reflects it to the beam splitter.

The post-imaging objective lens adopts an off-axis parabolic reflector to focus and image the refracted light and projected light on the rear reflective surface of the beam splitter, and reflect the formed image to the detector.

A rotary Fourier transform interference imaging spectrometer of the present invention also includes a rotary platform, the control port of the rotary platform is connected to the control and processing module, and the control and processing module controls the rotation of the rotary platform; the beam splitter is installed on the rotary platform , driven by the rotating platform, the beam splitter rotates around its center of symmetry relative to the cube-corner mirror group.

A rotary Fourier transform interference imaging spectrometer of the present invention also includes a rotary platform, the control port of the rotary platform is connected with the control and processing module, and the control and processing module controls the rotation of the rotary platform; the cube-corner mirror group is installed on On the rotating platform, driven by the rotating platform, the cube-corner mirror group rotates relative to the beam splitter around the center of symmetry of the beam splitter.

A rotary Fourier transform interference imaging spectrometer of the present invention has the following beneficial effects:

1) Compared with the slit interference imaging method adopted in the prior art, the present invention allows a clear aperture of any shape and size, which can reduce the loss of target light energy, so it has the characteristics of high luminous flux and high detection sensitivity;

2) The present invention replaces the traditional linear motion scanning mode of the moving mirror with the rotational scanning mode of the beam splitter, which avoids a series of technical difficulties caused by the precise linear scanning of the moving mirror; adopts the transverse shearing method based on the Michelson interference principle The interferometer has the characteristics of a common optical path. Even if the beam splitter shakes slightly during the rotation process, the interference effect will not be affected; the cube-corner mirror is used to replace the plane mirror in the traditional Fourier transform imaging spectrometer, which avoids the tilt of the plane mirror. bring about problems. All of these have improved the stability, reliability and shock resistance of the instrument, and made the structure of the invention more compact.

3) The device of the present invention can obtain a large amount of transverse shear through the rotation of the beam splitter, improve the spectral resolution to a certain extent, and greatly reduce the volume of the instrument under the condition of ensuring a large optical path difference.

4) The present invention is equivalent to adding a transverse shearing interferometer that changes the optical path difference through a rotating beam splitter in the ordinary imaging optical system, and utilizes the retroreflection characteristics of the cube-corner mirror. The principle and structure are simple and easy to process. Easy to adjust.

Description of drawings

Fig. 1 is a structural schematic diagram of an embodiment of a rotary Fourier transform interference imaging spectrometer of the present invention.

Fig. 2 is a structural schematic diagram of another embodiment of a rotary Fourier transform interference imaging spectrometer of the present invention.

Fig. 3 is the schematic diagram of the rotation and translation device of the present invention;

Fig. 4 is the schematic diagram of the pendulum mirror of the present invention;

Fig. 5 is a schematic structural diagram of a rotary Fourier transform interference imaging spectrometer disclosed by an embodiment of the present invention.

Among them, 1-front collimating objective lens, 2-beam splitter, 3-rotary platform, 4-first cube-corner mirror, 5-second cube-corner mirror, 6-rear imaging objective lens, 7-detector , 8-control and processing module, 9-fixture.

Detailed ways

The present invention will be described in detail below with reference to the accompanying drawings and examples.

The present invention provides a rotary Fourier transform interference imaging spectrometer, as shown in Figure 1, comprising a front collimating objective lens 1, a cube corner mirror, a beam splitter 2, a rear imaging objective lens 6, a detector 7 and Control and processing module 8, wherein, the front collimating objective lens 1 is placed in front of the target, the radiation beam of the target is converted into a parallel beam, the beam splitter 2 is placed in the optical path behind the front collimating objective lens 1, and the beam splitter The front and rear reflection surfaces of 2 form an angle of 45° with the parallel light beam; in this embodiment, the rotating platform 3 can be used to fix the beam splitter 2 on it, and the beam splitter 2 is symmetrical around it driven by the rotating platform 3 The center rotates in a plane parallel to the parallel beam.

There are two corner cube mirrors, which are respectively defined as a first corner cube mirror 4 and a second corner cube mirror 5, wherein the first corner cube mirror 4 is placed in the reflection light path of the beam splitter 2, and the first corner cube mirror The diagonal of the corner reflector 4 passes through the center of symmetry of the beam splitter 2, and forms an angle of 45° with the beam splitter 2; the second cube corner reflector 5 is located in the transmitted light path of the beam splitter 2, and the second cube corner reflector The mirror 5 and the first corner cube mirror 4 are distributed axisymmetrically with respect to the beam splitter 2 .

The rear imaging objective lens 6 is a Fourier transform lens, which is placed in the optical path of the beam splitter 2 on the side opposite to the first cube mirror, and is used for interferometric imaging of the two beams transmitted and refracted from the beam splitter 2 .

The detector 7 is placed on the focal plane of the rear imaging objective lens 6 for receiving the image plane interference pattern formed on the focal plane;

The control and processing module 8 is connected to the detector 7, controls the sampling frequency of the detector 7, and then stores and processes the interferogram of the image plane received by the detector 7, so as to obtain the spectral data cube of the target.

In the above scheme, the present invention scans the optical path difference by rotating the beam splitter 2 to complete interference spectrum imaging. According to the principle of relative motion, the angle of the beam splitter 2 can be fixed. As shown in Figure 2, the two The cube-corner mirrors are fixed together by a fixing device 9 to form a cube-corner mirror group, and the cube-corner mirror group is fixed on the rotating platform 3, driven by the rotating platform 3 around the center of symmetry of the beam splitter 2 in a parallel light beam Rotate in the parallel plane to achieve the purpose of optical path difference scanning.

In the present invention, the scanning of the target object plane can be realized in two ways: as shown in Figure 3, the first is to carry the entire spectrometer through the rotating translation device, drive the spectrometer to rotate, change the scanning window of the front collimating objective lens 1, and complete the scanning of the target Scanning action; as shown in Figure 4, the second is to add a oscillating mirror at the front end of the optical system, and change the field of view of the entrance pupil of the optical system through the rotation of the oscillating mirror to complete the scanning action on the target.

The working principle of a rotary Fourier transform interference imaging spectrometer of the present invention is:

The radiation beam from the target is converted into a parallel beam with an angle of view by the pre-collimated objective lens 1 and projected onto the beam splitter 2. The beam splitter 2 divides the collimated parallel beam into reflected beams with the same or similar intensity and transmitted beams. The reflected light beam split by the beam splitter 2 reaches the first corner cube mirror 4, and the first corner cube mirror 4 reflects the incident light back to the beam splitter 2 along the direction parallel to the incident light, and the light reflected back to the beam splitter 2 It is divided into a reflected light beam and a transmitted light beam again, and the transmitted light beam passes through the beam splitter 2 to reach the rear imaging objective lens 6 and is received by the detector 7 located on the focal plane of the rear imaging objective lens 6 .

The transmitted light beam split by the beam splitter 2 reaches the second corner cube mirror 5, and the second corner cube mirror 5 reflects its incident light back to the beam splitter 2 along a direction parallel to the incident light, and the light reflected back to the beam splitter 2 It is divided into a reflected light beam and a transmitted light beam again, and the reflected light beam passes through the beam splitter 2 to reach the rear imaging objective lens 6 and is received by the detector 7 located on the focal plane of the rear imaging objective lens 6 .

The reflected light beam split by the beam splitter 2 for the first time returns to the beam splitter 2 through the first cube-corner mirror 4, and converges to the detector 7 through the rear imaging objective lens 6 to form the optical path of the first beam of light; The transmitted light beam split by the beam splitter 2 for the first time, passes through the second square corner reflector, returns to the beam splitter 2, and converges to the detector 7 through the rear imaging objective lens 6 to form the optical path of the second beam of light; The two beams of light are obtained by laterally shearing the incident light by the beam splitter 2, and are two beams of coherent light, which produce a unified image of superimposed interference fringes on the detector 7.

During the rotation of the beam splitter 2, the optical path difference between the first beam and the second beam changes, and the phase difference of the two beams changes accordingly, and the interference spectrum of the two beams also changes. The detector 7 samples at a frequency that matches the rotational speed of the rotating platform 3, that is, a series of integrated images of maps and spectra can be obtained on the detector 7 to form an interference image cube. The control and processing module 8 reorganizes the interference image cube and performs Fourier transform to obtain the target spectral data cube.

The matching relationship between the sampling frequency of the detector 7 and the rotational speed of the rotating platform 3 is described below: when the beam splitter 2 starts to rotate, it scans from the zero point of the optical path difference. During the rotation of the beam splitter 2, the optical path difference changes continuously, then , the interference fringes move correspondingly on the interferogram of the image plane. When the rotational speed ω of the rotating platform 3 is constant, the moving speed of the image point changes. It is very important to match the speed of the rotating platform 3 with the sampling frequency of the detector 7.

It can be known by calculation that the distance between any image point and the zero optical path difference image point is y=f'sin(α)=f'sin(ωt), where t is the time required for the rotating platform 3 to turn over the α angle; The displacement velocity v _i of the image point is the derivative of the distance y to time t, then v _i =2ωf'cos(2ωt), f' is the focal length of the rear imaging objective lens 6, in order to enable the detector 7 to detect all interference The fringe requires the detector 7 to sample once, and the image point moves on the detector 7 at most by one detector unit. Therefore, the sampling frequency _q of the detector 7 and The relationship between the rotational speed ω of the rotating platform 3 satisfies Wherein, q is the sampling frequency of the detector 7, s is the size of the pixel of the detector 7, and α is the turning angle of the beam splitter 2, which can be measured by an instrument. According to the principle of relative motion, the matching relationship between the sampling frequency of the detector 7 and the rotational speed of the rotating platform 3 satisfies

As shown in Figure 5, it is an embodiment of the present invention, the front collimating objective lens 1 includes a front telescope 1 (a) and a reflective collimator, wherein the front telescope 1 (a) adopts a single off-axis parabolic reflector , focal length is 150mm, effective aperture The off-axis distance is 30mm, which has good imaging quality in the paraxial region; the reflective collimator 1(b) also uses an off-axis parabolic reflector the same as the front telescope 1(a), and its object focal point is the same as the front The image planes of the telescope 1(a) coincide; the incident light is collimated and becomes a parallel beam, which is projected to the central area of the beam splitter 2 at a certain angle. The beam splitter 2 uses a ZnSe plate with a compensation plate, the thickness is 6 mm, and the body diameter is 220 mm; the apex of the first cube-corner mirror 4 and the second cube-corner mirror 5 is at a position where the beam splitter 2 and the main axis form an angle of 45 degrees Axisymmetric, the distance between them and the beam splitter 2 is 200mm, their diameter is 200mm, and the surface is gold-plated; an off-axis design parabolic mirror is used for imaging; the focal length is 40mm, the effective aperture is 50×50mm, and the off-axis distance 30mm. For the focal plane detector 7, in the 1-5μm band, use a cooled PtSi-CCD array (512×512 pixels); in the thermal infrared 8-12μm band, use a cooled HgCdTe focal plane device or an uncooled infrared focal plane device (512 x 512 pixels). The image acquisition card is an ordinary video image acquisition card with a quantization precision of 8 bits, which is connected to the computer through the PCI bus. The signal processing system uses visual programming technology to complete functions such as image acquisition, noise processing, FFT transformation, and data storage. The single pixel size of the PtSi-CCD array is 30 μm, and the fringes of each period occupy two pixels on the detector 7, then the maximum optical path difference on the focal plane detector 7 is:

$\mathrm{<span\; class="notranslate">\; L</span>}<span\; class="notranslate">\; =</span><span\; class="notranslate">\; (</span>\frac{\mathrm{<span\; class="notranslate">\; 512</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}}<span\; class="notranslate">\; )</span><span\; class="notranslate">\; \&times;</span>\mathrm{<span\; class="notranslate">\; 8</span>}\mathrm{<span\; class="notranslate">\; \&mu;m</span>}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2048</span>}\mathrm{<span\; class="notranslate">\; \&mu;m</span>}$

Its wavenumber resolution is:

$\mathrm{<span\; class="notranslate">\; \&Delta;v</span>}<span\; class="notranslate">\; =</span>\frac{\mathrm{<span\; class="notranslate">\; 1</span>}}{\mathrm{<span\; class="notranslate">\; 2</span>}\mathrm{<span\; class="notranslate">\; L</span>}}<span\; class="notranslate">\; =</span>\mathrm{<span\; class="notranslate">\; 2.44</span>}{\mathrm{<span\; class="notranslate">\; cm</span>}}^{<span\; class="notranslate">\; -</span>\mathrm{<span\; class="notranslate">\; 1</span>}}$

To sum up, the above are only preferred embodiments of the present invention, and are not intended to limit the protection scope of the present invention. Any modifications, equivalent replacements, improvements, etc. made within the spirit and principles of the present invention shall be included within the protection scope of the present invention.

Claims (7)

1. a rotary Fourier transform inteference imaging spectrometer, is characterized in that, comprises preposition collimator objective (1), cube corner catoptron, beam splitter (2), rearmounted image-forming objective lens (6), detector (7) and control and processing module (8), wherein,

Described preposition collimator objective (1) is placed on the place ahead of target, converts the radiation laser beam of target to parallel beam, and beam splitter (2) is placed in the light path at preposition collimator objective (1) rear, beam splitter (2) and parallel beam angle at 45 °;

Described cube corner catoptron has two, be defined as respectively the first cube corner catoptron (4) and the second cube corner catoptron (5), wherein, the first cube corner catoptron (4) is placed in the reflected light path of beam splitter (2), the diagonal line of the first cube corner catoptron (4) is through the symcenter of beam splitter (2), and with beam splitter (2) angle at 45 °; The second cube corner catoptron (5) is arranged in the transmitted light path of beam splitter (2), and the second cube corner catoptron (5) and the first cube corner catoptron (4) are symmetric with respect to beam splitter (2); The first cube corner catoptron (4) and the second cube corner catoptron (5) form cube corner catoptron group;

Described beam splitter (2) and cube corner catoptron group are usingd the symcenter of beam splitter (2) and are relatively rotated as central point, for changing from the optical path difference of the two-way light beam of beam splitter (2) transmission and refraction;

Described rearmounted image-forming objective lens (6) is Fourier transform lens, is placed in the light path with the beam splitter (2) of the relative side of the first cube catoptron, for carrying out interference imaging from the two-way light beam of beam splitter (2) transmission and refraction;

Described detector (7) is placed on the focal plane of rearmounted image-forming objective lens (6), for being received in the image plane interference figure forming on this focal plane;

Described control is connected with detector (7) with processing module (8), controls on the one hand the sample frequency of detector (7), and the sample frequency q relation of detector (7) is met: wherein ω is beam splitter (2) and the speed that relatively rotates of cube corner catoptron group, and s is the size of detector (7) pixel, and f ' is the focal length of rearmounted image-forming objective lens (6), α be beam splitter (2) with cube corner catoptron group between the relative angle turning over; Control is stored and data processing with the image plane interference figure that processing module (8) receives detector (7) on the other hand, thereby obtains the spectroscopic data cube of target.

2. a kind of rotary Fourier transform inteference imaging spectrometer as claimed in claim 1, is characterized in that, also comprises rotational translation device, is used for driving whole inteference imaging spectrometer rotation, changes thus the scanning window of imaging device.

3. a kind of rotary Fourier transform inteference imaging spectrometer as claimed in claim 1, it is characterized in that, also comprise and be placed on the front pendulum mirror of preposition collimator objective (1), pendulum mirror arrives target emanation beam reflection on preposition collimator objective (1), and change optical system entrance pupil visual field by the rotation of pendulum mirror, change thus the scanning window of imaging device.

4. a kind of rotary Fourier transform inteference imaging spectrometer as claimed in claim 1, it is characterized in that, described preposition collimator objective (1) is comprised of two off-axis parabolic mirrors, be defined as respectively the first off-axis parabolic mirror and the second off-axis parabolic mirror, wherein the focus in object space of the second off-axis parabolic mirror overlaps with the image planes position of the first off-axis parabolic mirror; The first off axis paraboloid mirror reflecting surface to the second off-axis parabolic mirror, collimates back reflection to beam splitter (2) through it by the beam reflection of target emanation.

5. a kind of rotary Fourier transform inteference imaging spectrometer as claimed in claim 1, it is characterized in that, described rearmounted image-forming objective lens (6) adopts off axis paraboloid mirror transmitting mirror, the refract light of the back reflection face of beam splitter (2) and projection light are carried out to focal imaging, and imaging is reflexed on detector (7).

6. a kind of rotary Fourier transform inteference imaging spectrometer as claimed in claim 1, it is characterized in that, also comprise rotation platform (3), the control port of rotation platform (3) is connected with processing module with control, controls the rotation of controlling rotation platform (3) with processing module; It is upper that described beam splitter (2) is arranged on rotation platform (3), and under the drive of rotation platform (3), beam splitter (2) rotates with respect to cube corner catoptron group around its symcenter.

7. a kind of rotary Fourier transform inteference imaging spectrometer as claimed in claim 1, it is characterized in that, also comprise rotation platform (3), the control port of rotation platform (3) is connected with processing module with control, controls the rotation of controlling rotation platform (3) with processing module; It is upper that described cube corner catoptron group is arranged on rotation platform (3), and under the drive of rotation platform (3), cube corner catoptron group is rotated with respect to beam splitter (2) around the symcenter of beam splitter (2).