CN101471532B - Frequency-doubling method capable of preventing frequency-doubling recede transition and laser - Google Patents

Abstract

The invention relates to a frequency doubling method capable of obviating reverse conversion and a laser. The method comprises the following steps: (1) doubling the frequency of a fundamental beam generated by a laser source through a frequency doubling material, and splitting the frequency-doubled beam into two beams by a dichroic mirror; (2) changing the polarization direction of one frequency-doubled beam generated by a first single pass through a 1/4 wave plate of a frequency-doubled beam and a reflector, and returning to the frequency doubling material; (3) reflecting the residual fundamental beam in the first single pass to the frequency doubling material to carry out second frequency doubling; and (4) splitting a double-pass frequency-doubled beam from the frequency doubling material and the residual fundamental beam in the second single pass into two beams by a dichroic mirror, outputting the double-pass frequency-doubled beam, and returning the residual fundamental beam in the second single pass. By rotating the polarization direction of the frequency-doubled beam of the first single pass by 90 DEG, the method can prevent reverse conversion of the frequency-doubled beam to the fundamental beam, thereby improving the laser frequency doubling conversion efficiency. The method can be widely used in various kinds of intracavity and extracavity solid-state lasers.

Description

A frequency doubling method and laser capable of preventing frequency doubling deconversion

technical field

The invention relates to a laser, in particular to a frequency doubling method capable of preventing frequency doubling deconversion and a laser.

Background technique

When designing a solid-state laser that uses the nonlinear effect of nonlinear materials to obtain frequency-doubled laser output, it is generally desirable to obtain high-power laser output. All-solid-state frequency-doubling lasers are divided into two categories: external cavity and internal cavity. The former is generally low in conversion efficiency due to the low power density of the fundamental wave outside the cavity; the latter directly uses the higher fundamental power density in the cavity. Therefore, nonlinear transformation can be performed efficiently. The fundamental frequency light in the cavity type generally adopts a two-way way to pass through the nonlinear material to generate frequency doubled light back and forth. The original intention of this method is to extend the length of the interaction between the laser and the nonlinear material in order to convert as much fundamental frequency light as possible into frequency-doubled light, and the frequency-doubled light generated by this double pass is output together. However, in this two-way output method, when the doubled frequency light increases to a certain intensity, "deconversion" will occur, that is, the conversion of the doubled frequency light to the fundamental frequency light will occur, so that the frequency doubled output power and frequency doubled Reduced efficiency.

David Eimerl in "Quadrature Frequency Conversion" (IEEEJournal of Qantum Electronics, Vol.QE-23, No.8, 1987), using cascaded bilinear materials for Type II phase-matched frequency doubling , the two are cut in such a way that the fast light and slow light directions in the first material are the slow light and fast light directions in the second material, respectively. The remaining fundamental frequency light in the first material still satisfies the phase matching condition in the second material, and continues to generate frequency doubled light, but the polarization direction of the doubled frequency light generated in the first material is perpendicular. Therefore, when the frequency-doubled light generated in the first nonlinear material is transmitted to the second material, the deconversion to the fundamental frequency light will not occur because the phase matching condition is not satisfied. This method requires the use of two separate doubling materials and is only suitable for Type II phase-matched doubling processes.

Raymond G. Beausoleil, Redmond, Wash of Cygnus Laser Corporation still uses cascaded frequency doubling materials in US Patent 5,247,389 "Nonliner Optical Frequency Converter (Nonlinear Optical Frequency Converter)". Since a wave plate is used between the two materials, the polarization direction of the frequency-doubled light generated in the first material is rotated by 90 degrees, so the frequency-doubled light in the second material does not meet the phase matching, so no "" back conversion".

In the above-mentioned documents, two pieces of nonlinear materials are required. Although it is mentioned in US Patent No. 5,247,389 that a single piece of nonlinear material and a wave plate can be used to prevent deconversion, to achieve this method requires a dispersive wave piece.

Contents of the invention

In view of the above problems, the object of the present invention is to provide a frequency doubling method and a laser that can prevent frequency doubling de-conversion.

To achieve the above object, the present invention takes the following technical solutions:

A frequency doubling method capable of preventing frequency doubling deconversion, comprising the following steps: (1) after the fundamental frequency light emitted by a laser source is frequency-doubled by a frequency doubling material, it is divided into two paths by a dichroic mirror; (2) ) After the frequency-doubled light generated by the first one-way pass through a 1/4 wave plate of the frequency-doubled light and a reflector to change the polarization direction, return and pass through the frequency-doubled material; (3) pass the first one-way remaining The fundamental frequency light is reflected back to the frequency doubling material by a reflector, and the frequency doubling is carried out for the second time; (4) the two-way frequency doubling light coming out from the frequency doubling material and the second one-way remaining fundamental frequency light, Divided into two paths by a dichroic mirror, the two-way frequency doubled light is output, and the second one-way remaining fundamental frequency light is returned.

A frequency doubling laser capable of preventing frequency doubling deconversion, which includes a laser source generating fundamental frequency light, a cavity mirror, a frequency doubling material, and a dichroic mirror arranged at both ends of the frequency doubling material; it is characterized in that: The dichroic mirror at the rear of the frequency material is provided with a 1/4 wave plate of frequency doubled light and a mirror, so that the frequency doubled light generated in the first one-way pass back and forth after the 1/4 wave plate of the frequency doubled light , the polarization direction is rotated by 90°.

The fundamental frequency light emitted by the laser source is the fundamental frequency light emitted by the laser material provided in the cavity laser.

The fundamental frequency light emitted by the laser source is the fundamental frequency light emitted by the external cavity laser and incident through the optical isolator.

The frequency doubling material is cut according to a type I phase matching angle.

The frequency doubling material is cut according to type II phase matching angle.

The fundamental frequency light is continuous output laser light.

The fundamental frequency light is pulse output laser.

Because the present invention adopts the above technical scheme, it has the following advantages: 1. The present invention adopts the mode of changing the polarization direction by 90 degrees by passing the frequency-doubled light through the wave plate, so that the frequency-doubled light generated for the first time is in the return process, No longer meet the phase matching conditions, so it will not be converted into fundamental frequency light; and the remaining fundamental frequency light in the first single pass can continue to be converted into frequency doubled light because it still meets the phase matching condition when returning, so that The frequency doubled light generated by the two-way can be effectively output, which improves the frequency double conversion efficiency. 2. Due to the improvement of the frequency doubling conversion efficiency of the present invention, under the same fundamental frequency optical power density, a higher power frequency doubling light can be obtained; at the same time, the present invention can prevent frequency doubling without using a wave plate with dispersion purpose of conversion. The invention can be widely used in various internal and external cavity solid-state lasers. .

Description of drawings

FIG. 1 is an embodiment of an intracavity frequency multiplier for Type I phase matching and Type II phase matching according to the present invention.

Fig. 2 is the embodiment of external cavity type frequency multiplication used for type I phase matching and type II phase matching of the present invention

Detailed ways

Example 1:

As shown in FIG. 1 , this embodiment adopts a type I phase-matched inner-cavity frequency multiplier. LM is Nd:YAG laser material, NLC is LBO frequency doubling material cut according to type I phase matching angle, WP is 1/4 wave plate of 532nm frequency doubling light, cavity mirrors M1 and M2 are highly reflective to 1064nm fundamental frequency light, The dichroic mirror M3 is highly reflective to 1064nm fundamental frequency light and highly transparent to 532nm frequency doubled light, the dichroic mirror M4 is highly transparent to 1064nm and highly reflective to 532nm, and the mirror M5 is highly reflective to 532nm.

The laser generated by Nd:YAG is in the "P" polarization state. After frequency doubling by LBO, a 532nm laser in the "S" polarization state is generated. After the frequency doubled light is reflected by the dichroic mirror M4, it passes through the 1/4 wave plate WP back and forth. The polarization direction is rotated by 90 degrees to become the "P" polarization state. In the return process, the 1064nm fundamental frequency light reflected by the cavity mirror M2 continues to be converted by the LBO frequency doubling material into the 532nm frequency doubling light of the "S" polarization state, and the 532nm frequency doubling light generated in the first single pass is due to the It becomes the "P" polarization state and no longer satisfies the phase matching condition, so it will not be back-converted into the fundamental frequency light, and the frequency doubled light generated by the two-way pass is finally output through the dichroic mirror M3. After the remaining fundamental frequency light is reflected by M3, it continues to oscillate and amplify in the cavity.

Example 2:

This embodiment adopts the type II phase-matching internal cavity frequency doubling. LM is Nd:YVO4 laser material, NLC is KTP frequency doubling material cut according to type II phase matching angle, WP is 1/4 wave plate of 532nm frequency doubling light, cavity mirrors M1 and M2 are highly reflective to 1064nm fundamental frequency light, The dichroic mirror M3 is highly reflective to 1064nm fundamental frequency light and highly transparent to 532nm frequency doubled light, the dichroic mirror M4 is highly transparent to 1064nm and highly reflective to 532nm, and the mirror M5 is highly reflective to 532nm.

The polarization direction of the laser generated by Nd:YVO4 is at an angle of 45 degrees to the paper surface. After frequency doubling by KTP, a 532nm laser with "S" polarization is generated. The frequency doubling light is reflected by the dichroic mirror M4 and passes through 1/4 wave back and forth. For sheet WP, the polarization direction is rotated by 90 degrees and becomes "P" polarization state. In the return process, the 1064nm fundamental frequency light continues to be converted into the 532nm frequency doubled light of the "S" polarization state, and the 532nm frequency doubled light generated in the first single pass has become the "P" polarization state, no longer The phase matching condition is met, so it will not be back-converted into the fundamental frequency light, and the frequency doubled light generated by the two-way pass is finally output through the dichroic mirror M3. After the remaining fundamental frequency light is reflected by M3, it continues to oscillate and amplify in the cavity.

Embodiment 3: As shown in FIG. 2 , this embodiment adopts type I phase-matched external cavity frequency doubling. FL is the fundamental frequency light, P is the optical isolator, NLC is the LBO frequency doubling material cut according to the type I phase matching angle, WP is the 1/4 wave plate of the 532nm frequency doubling light, dichroic mirrors M1 and M2 are for 1064nm High transmission of fundamental frequency light, high reflection of 532nm frequency doubled light, mirror M3 high reflection of 1064nm fundamental frequency light, and reflector M4 high reflection of 532nm frequency doubled light.

The FL fundamental frequency light passing through the optical isolator P is in the "P" polarization state, and after being frequency-doubled by LBO, a 532nm laser in the "S" polarization state is generated. After the frequency-doubled light is reflected by the dichroic mirror M2, it passes through 1/4 back and forth With the wave plate WP, the polarization direction is rotated by 90 degrees and becomes the "P" polarization state. The 1064nm fundamental frequency light transmitted by the dichroic mirror M2 and reflected by the mirror M3 is converted into the 532nm frequency doubled light of the "S" polarization state through the LBO frequency doubling during the return process, and is generated in the first one-way Since the 532nm frequency-doubled light has become "P" polarization state, when it returns to pass through the LBO, it no longer satisfies the phase matching condition, so it will not be back-converted into the fundamental frequency light. The frequency doubled light generated by the two-way pass is finally reflected and output by the dichroic mirror M1, and the optical isolator P prevents the remaining fundamental frequency light from returning and damaging other optical devices.

The above-mentioned embodiment 3 may also adopt the type II phase-matching external-cavity frequency doubling method, and the situation is roughly the same as that of the above-mentioned embodiment 3, so it will not be described again.

Claims (10)

1. A frequency multiplication method capable of preventing frequency multiplication from de-converting, comprising the following steps: (1) Pass the fundamental frequency light emitted by the laser source through a frequency-doubling material, and after the first one-way frequency doubling, pass the frequency-doubling light generated by the first one-way and the remaining fundamental frequency light of the first one-way through the first two-way The dichroic mirror splits into two paths; (2) After being reflected by the first dichroic mirror, the frequency-doubled light generated by the first one-way pass through a 1/4 wave plate to a reflector and then reflected by the reflector and pass through the 1/4 wave again sheet, the polarization direction is rotated by 90°, and returns to and passes through the frequency-doubling material; (3) After the first one-way remaining fundamental frequency light is transmitted through the first dichroic mirror, it is reflected by a cavity mirror and then transmitted through the first dichroic mirror, and returns to the frequency doubling material, Do a second one-way multiplier; (4) The two-way frequency-doubling light coming out of the frequency-doubling material and the remaining fundamental frequency light of the second one-way are divided into two paths through the second dichroic mirror, and the two-way frequency-doubling light is output, and the The remaining fundamental frequency light in the second single pass continues to oscillate in the cavity and is amplified or output out of the cavity and blocked by the optical isolator. 2. A kind of frequency doubling method capable of preventing frequency doubling de-conversion as claimed in claim 1, characterized in that: the fundamental frequency light emitted by the laser source is the fundamental frequency light emitted by the laser material arranged in the cavity laser . 3. A kind of frequency doubling method capable of preventing frequency doubling deconversion as claimed in claim 1, characterized in that: the fundamental frequency light emitted by the laser source is the fundamental frequency emitted by an external cavity laser and incident through an optical isolator Light. 4. A frequency doubling method capable of preventing frequency doubling deconversion according to claim 1, 2 or 3, characterized in that: the nonlinear material is cut according to a type I phase matching angle. 5. A frequency doubling method capable of preventing frequency doubling deconversion according to claim 1, 2 or 3, characterized in that: the nonlinear material is cut according to a type II phase matching angle. 6. A frequency doubling method capable of preventing frequency doubling de-conversion according to claim 1, 2 or 3, characterized in that: the fundamental frequency light is continuously output laser light. 7. A frequency doubling method capable of preventing deconversion of frequency doubling as claimed in claim 1, 2 or 3, characterized in that: the fundamental frequency light is pulse output laser. 8. A frequency doubling laser that can prevent frequency doubling from de-converting, it includes a laser source of incident fundamental frequency light, a cavity mirror, a frequency doubling material, and a dichroic mirror arranged at the two ends of the frequency doubling material; it is characterized in that: A dichroic mirror between the frequency doubling material and the cavity mirror is provided with a 1/4 wave plate and a reflector of the frequency doubling light, so that the frequency doubling light generated in the first single pass is captured by the two After being reflected by the chromatic mirror, it passes through the 1/4 wave plate of the frequency doubled light back and forth, and the polarization direction is rotated by 90°. The fundamental frequency light emitted by the laser source is the fundamental frequency emitted by the external cavity laser and incident through the optical isolator The light or the fundamental frequency light emitted by the laser material provided in the cavity laser. 9. A frequency doubling laser capable of preventing frequency doubling de-conversion as claimed in claim 8, wherein the frequency doubling material is a frequency doubling material cut according to a type I phase matching angle. 10. A frequency doubling laser capable of preventing frequency doubling deconversion according to claim 8, wherein the frequency doubling material is a frequency doubling material cut according to a type II phase matching angle.

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