CN113507035A - Laser nonlinear wavelength conversion system - Google Patents

Laser nonlinear wavelength conversion system Download PDF

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Publication number
CN113507035A
CN113507035A CN202111057011.XA CN202111057011A CN113507035A CN 113507035 A CN113507035 A CN 113507035A CN 202111057011 A CN202111057011 A CN 202111057011A CN 113507035 A CN113507035 A CN 113507035A
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light
crystal
nonlinear
laser
nonlinear crystal
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彭艳红
杨毅
李代勇
邬德勇
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Sichuan Guangtianxia Laser Technology Co ltd
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Sichuan Guangtianxia Laser Technology Co ltd
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    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/10Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating
    • H01S3/106Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity
    • H01S3/108Controlling the intensity, frequency, phase, polarisation or direction of the emitted radiation, e.g. switching, gating, modulating or demodulating by controlling devices placed within the cavity using non-linear optical devices, e.g. exhibiting Brillouin or Raman scattering
    • H01S3/109Frequency multiplication, e.g. harmonic generation
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/005Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping
    • H01S3/0071Beam steering, e.g. whereby a mirror outside the cavity is present to change the beam direction
    • HELECTRICITY
    • H01ELECTRIC ELEMENTS
    • H01SDEVICES USING THE PROCESS OF LIGHT AMPLIFICATION BY STIMULATED EMISSION OF RADIATION [LASER] TO AMPLIFY OR GENERATE LIGHT; DEVICES USING STIMULATED EMISSION OF ELECTROMAGNETIC RADIATION IN WAVE RANGES OTHER THAN OPTICAL
    • H01S3/00Lasers, i.e. devices using stimulated emission of electromagnetic radiation in the infrared, visible or ultraviolet wave range
    • H01S3/02Constructional details
    • H01S3/04Arrangements for thermal management
    • H01S3/0405Conductive cooling, e.g. by heat sinks or thermo-electric elements

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  • Electromagnetism (AREA)
  • Engineering & Computer Science (AREA)
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  • Optics & Photonics (AREA)
  • Nonlinear Science (AREA)
  • Optical Modulation, Optical Deflection, Nonlinear Optics, Optical Demodulation, Optical Logic Elements (AREA)

Abstract

The invention provides a laser nonlinear wavelength conversion system, which belongs to the field of solid lasers and comprises a heat sink, a dichroic mirror and a surface coated with SiO2The laser comprises a nonlinear crystal of a protective film and a sapphire crystal with one surface plated with a total reflection film, wherein the total reflection film is used for reflecting fundamental frequency light and laser after nonlinear conversion; nonlinear crystal SiO2One side of the protective film is in optical cement with one side of the sapphire full-reflection film, and the other side of the sapphire crystal is welded with the heat sink; the dichroic mirror is positioned on the non-linear crystal and is not coated with SiO2And one side of the protective film is used for separating the laser after the fundamental frequency light and the nonlinear conversion. According to the invention, the fully-reflecting film is arranged between the nonlinear crystal and the heat sink, and fundamental light is totally reflected when the fundamental light is subjected to walk-off incidence to the fully-reflecting film through the nonlinear crystal, so that the influence of the shape of a light spot and the frequency doubling efficiency caused by the walk-off effect when the fundamental light is emitted from the nonlinear crystal is improved; for at the same timeThe large surface of the linear crystal dissipates heat, and the heat dissipation speed is improved.

Description

Laser nonlinear wavelength conversion system
Technical Field
The invention belongs to the field of solid lasers, and particularly relates to a laser nonlinear wavelength conversion system.
Background
In the frequency doubling process of the nonlinear crystal, as the nonlinear crystal absorbs part of laser energy, when the incident fundamental frequency light is large-energy and high-repetition-frequency laser, the temperature is easily increased due to heat accumulation in the crystal, the phase matching condition is damaged, the frequency doubling conversion efficiency and stability are greatly reduced, and meanwhile, the nonlinear crystal can be deformed or even broken.
Generally speaking, the length of the nonlinear crystal is generally several millimeters to tens of millimeters, in the prior art, the nonlinear crystal is usually mounted on a heat conduction material, heat dissipation is realized from four sides of the nonlinear crystal, in order to achieve a good heat dissipation effect, the nonlinear crystal can only be made into a small block with a small cross section area, and the size of an incident light beam is greatly limited. The small blocky nonlinear crystal is subjected to heat dissipation from four side faces, the requirement on a heat dissipation structure is high, actual heat dissipation is inevitably insufficient, and the phase mismatch is easily caused by a heat effect, so that the frequency doubling efficiency is influenced. For a large-energy high-power laser, the power density must be extremely large due to the small beam size, and the power density completely exceeds the damage threshold of the nonlinear crystal, and the existing heat dissipation mode is not enough to meet the incidence of fundamental frequency light with the large beam size.
Disclosure of Invention
Aiming at the problems in the prior art, the invention provides a laser nonlinear wavelength conversion system to improve the heat dissipation effect of a nonlinear crystal so as to carry out nonlinear wavelength conversion on fundamental frequency light with large energy and high power.
The specific technical scheme of the invention is as follows:
a laser nonlinear wavelength conversion system is characterized by comprising a heat sink, a dichroic mirror and a surface coated with SiO2The laser comprises a nonlinear crystal of a protective film and a sapphire crystal with one surface plated with a total reflection film, wherein the total reflection film is used for reflecting fundamental frequency light and laser after nonlinear conversion; SiO of the nonlinear crystal2One side of the protective film is in optical cement with one side of the totally-reflecting film of the sapphire crystal, and the other side of the sapphire crystal is welded with the heat sink; the dichroic mirror is positioned on the non-linear crystal and is not coated with SiO2One side of the protective film for separating the fundamental frequency light from the nonlinear conversionThe laser of (1); the laser after nonlinear conversion is frequency doubling light, sum frequency light or difference frequency light.
Further, the SiO2The thickness of the protective film is 50-200 nm.
Further, the nonlinear crystal is a flaky crystal.
Further, a heat sink with one surface plated with a full-reflection film is adopted to replace a welded sapphire crystal and a heat sink, namely SiO of a nonlinear crystal2One surface of the protective film is directly in optical cement with one surface of the totally reflecting film of the heat sink; the total reflection film is used for reflecting the fundamental frequency light and the laser after nonlinear conversion, and the laser after nonlinear conversion is frequency doubling light, sum frequency light or difference frequency light.
Further, gold, titanium and first SiO are sequentially plated on the surface of the heat sink between the heat sink and the total reflection film2Layer and plating a second SiO on the other side of the total reflection film2A layer; the second SiO2The thickness of the layer was 5 μm.
The invention has the beneficial effects that:
1. the invention provides a laser nonlinear wavelength conversion system, which is characterized in that a layer of total reflection film is arranged between a nonlinear crystal and a heat sink, when fundamental frequency light is totally reflected when the fundamental frequency light is subjected to walk-off incidence to the total reflection film by the nonlinear crystal and then is emitted from the nonlinear crystal, the influence of the walk-off effect on the shape of a spot and the frequency doubling efficiency is improved, and compared with the traditional nonlinear crystal with a smaller incident beam size and a longer length, the influence of the walk-off effect is obviously reduced;
2. when the nonlinear crystal is preferably a flaky crystal with a large incident area, on one hand, the walk-off effect is not obvious, and on the other hand, the large surface (namely the surface with the sapphire crystal or the surface with the heat sink optical cement) of the nonlinear crystal is used for heat dissipation, so that the heat dissipation speed of the nonlinear crystal can be improved; and because the nonlinear crystal is in a sheet shape, the laser direction is consistent with the heat flow direction, and the nonlinear crystal does not have a thermal lens effect, the nonlinear crystal can carry out frequency doubling, sum frequency or difference frequency on fundamental frequency light with large energy and high repetition frequency.
Drawings
Fig. 1 is a schematic structural diagram of a laser nonlinear wavelength conversion system proposed in embodiment 1;
FIG. 2 is a schematic view of the exit direction of incident light e in example 1;
FIG. 3 is a schematic view of the exit direction of reflected light e in example 1;
fig. 4 is a schematic structural diagram of a laser nonlinear wavelength conversion system according to embodiment 2;
the reference numbers are as follows:
11: a first nonlinear crystal; 12: a second nonlinear crystal; 13: a third nonlinear crystal; 21: a first sapphire crystal; 22: a second sapphire crystal; 31: a first dichroic mirror; 32: a second dichroic mirror; 33: a third dichroic mirror; 34: a fourth dichroic mirror; 41: a first heat sink; 42: a second heat sink.
Detailed Description
In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention will be further described with reference to the following embodiments and the accompanying drawings.
The following non-limiting examples are presented to enable those of ordinary skill in the art to more fully understand the present invention and are not intended to limit the invention in any way.
Example 1
A laser nonlinear wavelength conversion system is structurally shown in figure 1 and comprises a first nonlinear crystal 11, a second nonlinear crystal 12, a first sapphire crystal 21, a second sapphire crystal 22, a first dichroic mirror 31, a second dichroic mirror 32 and a first heat sink 41. Fig. 2 and 3 are schematic diagrams of the walk-off directions of incident light e and reflected light e, respectively. The wavelength of the fundamental frequency light used is 1064 nm.
The first nonlinear crystal 11 is made of negative uniaxial BBO (barium metaborate) crystal, 1064nm fundamental frequency light is converted into 532nm light through the first nonlinear crystal 11, and the optimal phase matching angle theta of I-type phase matching between 1064nm and 532nm is the optimal phase matching angle theta1=22.8 degrees, in order to make an included angle between a 1064nm fundamental frequency light wave vector direction incident vertical to the surface of the first nonlinear crystal 11 and the optical axis of the negative uniaxial BBO crystal form an optimal phase matching angle theta1The machining cut angle of the negative uniaxial BBO crystal used for the first nonlinear crystal 11 is required to be equal to the optimum phase matching angle theta1(ii) a First, theOne surface of a nonlinear crystal 11 is coated with SiO with the thickness of 200 nm2A protective film which polishes the surface; light is incident from the other side of the first nonlinear crystal 11, and the incident end face size is 10 × 10 mm, and the thickness is 2 mm.
The size of the first sapphire crystal 21 is larger than or equal to that of the first nonlinear crystal 11, one surface of the first sapphire crystal is plated with a total reflection film of 1064nm and 532nm, and then is plated with SiO2A protective film which is polished and then coated with SiO to the first nonlinear crystal 112One side of the protective film is polished with glue. Because the surface flatness of the first sapphire crystal 21 plated with the full-reflection film can not meet the requirement of the optical cement, a layer of SiO is plated2Protective film of p-SiO2The protective film is polished to avoid damaging the full-reflection film during polishing.
The first dichroic mirror 31 is located on the first nonlinear crystal 11 without SiO plating2One side of the protective film is totally transparent to 1064nm fundamental frequency light and totally reflective to 532nm light.
The second nonlinear crystal 12 is made of negative uniaxial BBO crystal, 532nm light is converted into 266 nm light through the second nonlinear crystal 12, and the optimal phase matching angle theta of class I phase matching from 532nm to 266 nm2=47.6 °, in order to make the angle between the wave vector direction of the 532nm fundamental frequency light incident perpendicularly to the surface of the second nonlinear crystal 12 and the optical axis of the negative uniaxial BBO crystal be the optimal phase matching angle θ2The second nonlinear crystal 12 is required to adopt a corner cut processing method similar to that of the first nonlinear crystal 11, i.e., the processing corner cut of the negative uniaxial BBO crystal is equal to the optimum phase matching angle theta2(ii) a One side of the second nonlinear crystal 12 is coated with 200 nm thick SiO2A protective film which polishes the surface; light is not SiO-coated from the second nonlinear crystal 122One side of the protective film is incident, the size of the incident end face is 10 × 10 mm, and the thickness is 2 mm.
The size of the second sapphire crystal 22 is larger than or equal to that of the second nonlinear crystal 12, one side of the second sapphire crystal is plated with 532nm and 266 nm full-reflection films, and then a layer of SiO with the thickness of 5 mu m is plated2A protective film which is polished and then coated with SiO to the second nonlinear crystal 122One side of the protective film is polished with glue.
The second dichroic mirror 32 is positioned on the second nonlinear crystal 12 without SiO plating2One side of the protective film is totally reflective to 532nm light and totally transparent to 266 nm light.
After being fully transmitted by the first dichroic mirror 31, the 1064nm fundamental frequency light enters the first nonlinear crystal 11 to perform 1064nm to 532nm class I phase matching, the 1064nm fundamental frequency light and the 532nm frequency doubling light generated during incidence are reflected by a total reflection film, the 1064nm fundamental frequency light continues to be frequency doubled to generate 532nm frequency doubling light, the 532nm frequency doubling light is emitted by the first nonlinear crystal 11, the 532nm frequency doubling light is sequentially reflected by the first dichroic mirror 31 and the second dichroic mirror 32 to the second nonlinear crystal 12 to perform 532nm to 266 nm class I phase matching, the 532nm light and the 266 nm frequency doubling light generated during incidence are reflected by the total reflection film of the second sapphire crystal 2-2, the 532nm light continues to be frequency doubled to generate 266 nm frequency doubling light, the 266 nm frequency doubling light is emitted by the second nonlinear crystal 12, and then the 266 nm frequency doubling light is totally transmitted by the second dichroic mirror 32.
The first sapphire crystal 21 and the second sapphire crystal 22 are indium-welded on the first heat sink 41 for accelerating heat dissipation.
Since the total reflection film is generally thick, the total reflection film cannot be directly plated on the surface of the nonlinear crystal (including the first nonlinear crystal 11 and the second nonlinear crystal 12) or the film layer is not firm after plating, so that the total reflection film is plated on the surface of the sapphire crystal (including the first sapphire crystal 21 and the second sapphire crystal 22). The total reflection film reflects the fundamental frequency light and the frequency doubling light, so that the incidence of the fundamental frequency light and the emergence of the frequency doubling light are realized on the same large surface, and the nonlinear crystal (comprising the first nonlinear crystal 11 and the second nonlinear crystal 12) can be radiated on the other large surface (the large surface optically glued with the sapphire crystal).
In a large-surface optical cement sapphire crystal (including the corresponding first sapphire crystal 21 and second sapphire crystal 22) of the nonlinear crystal (including the first nonlinear crystal 11 and the second nonlinear crystal 12), the contact area is large, the heat conduction coefficient of sapphire is large, heat dissipation is fast, and meanwhile, the sapphire crystal (including the first sapphire crystal 21 and the second sapphire crystal 22) is indium-welded on the first heat sink 41, so that the heat dissipation speed is accelerated. The sapphire crystal (including the first sapphire crystal 21 and the second sapphire crystal 22) is equivalent to end face cooling of the nonlinear crystal (including the first nonlinear crystal 11 and the second nonlinear crystal 12), the crystal with large incident end face area and thin thickness adopts end face cooling, heat dissipation is fast, and cooling effect is good. And because the nonlinear crystal is in a sheet shape, the laser direction is consistent with the heat flow direction, and the nonlinear crystal does not have the thermal lens effect. Meanwhile, the area of the incident end face is large, so that the size of a light spot of the fundamental frequency light can be increased by several times compared with that of a traditional small blocky or strip-shaped nonlinear crystal, the power density of the laser with large energy and high power is greatly reduced, and the damage threshold of the nonlinear crystal (including the first nonlinear crystal 11 and the second nonlinear crystal 12) is avoided.
Because the incident beam size is large and the thickness of the nonlinear crystal (including the first nonlinear crystal 11 and the second nonlinear crystal 12) is thin, the deformation amount of the light spot caused by walk-off is not obvious for the large-size light spot; the degree of beam separation caused by walk-off is also not significant to the overall degree of beam overlap.
In this example, a negative uniaxial BBO crystal is used, the laser light is converted from 1064nm to 532nm, which belongs to class i phase matching of o + o → e, and the incident fundamental frequency light is assumed to be a circular spot with a diameter of b. When incident, the direction of e-ray departure in the first nonlinear crystal 11 is shown in fig. 2, and the long dashed line is the optical axis direction. In the first nonlinear crystal 11BBO, the fundamental frequency light of 1064nm is o light, and the wavevector thereof is
Figure 530374DEST_PATH_IMAGE001
Direction and energy flow density
Figure 439424DEST_PATH_IMAGE002
The directions are consistent, and the walking-away phenomenon does not occur; 532nm frequency doubled light is e light, and the wave vector of the e light
Figure 243432DEST_PATH_IMAGE003
Wave vector of direction and o-light
Figure 441195DEST_PATH_IMAGE001
With uniform direction, 532nmWave vector of frequency-doubled e-ray
Figure 972539DEST_PATH_IMAGE003
Direction and energy flow density
Figure 736096DEST_PATH_IMAGE004
Direction is shown in FIG. 2, wave vector
Figure 976584DEST_PATH_IMAGE003
Direction and energy flow density
Figure 130485DEST_PATH_IMAGE004
The directions are not consistent, so that 532nm frequency doubling light is separated, and the separation angle is alpha. The walk-off effect will cause the beams of o-light and e-light to separate, affecting the beam quality. Because the 1064nm fundamental frequency light is not separated all the time, the point A also generates frequency doubling conversion, the circular light spot is farthest separated to the point B, the frequency doubling light spot of the total reflection film is an elliptical light spot, and if the thickness of the first nonlinear crystal 11 is z, the major axis of the elliptical light spot is
Figure 481832DEST_PATH_IMAGE005
And the minor axis is b. After the fundamental frequency light of 1064nm and the frequency doubling light of 532nm are reflected by adopting a total reflection film, the o light still does not leave, and is emitted in the reverse incidence direction. However, since the direction of the optical axis of the first nonlinear crystal 11 is not changed, the e-wave vector
Figure 99895DEST_PATH_IMAGE006
The direction is reversed, so that the direction of the frequency-doubled light is away from
Figure 763482DEST_PATH_IMAGE007
Reverse direction is the inverse
Figure 404679DEST_PATH_IMAGE004
Therefore, 532nm frequency-doubled light generated at point A will go away to point A ', and 532nm frequency-doubled light going away to point B will go away to point B' in reverse direction, as shown in FIG. 3, the emergent frequency-doubled light spot still has a major axis
Figure 294138DEST_PATH_IMAGE005
And the minor axis is an elliptical spot of b.
In this embodiment, the fundamental light enters the first nonlinear crystal 11, and after entering and reflecting, it passes through a nonlinear crystal having a thickness of 2z, and the long axis of the emitted frequency-doubled light is
Figure 235549DEST_PATH_IMAGE005
(ii) a When the passing thickness is 2z, the long axis of the emitted frequency doubling light is
Figure 614578DEST_PATH_IMAGE008
Therefore, the present embodiment utilizes the total reflection film to reflect the fundamental frequency light and the frequency doubling light, and further improves the influence of the walk-off effect on the spot size of the outgoing light beam.
Similarly, for a positive uniaxial crystal of which two fundamental frequency lights are both e lights, the I-type phase matching belonging to e + e → o is adopted, when the wavelengths of the two fundamental frequency lights are the same, the walk-off directions are consistent, and the walk-off only influences the shape of a light spot; however, when the wavelengths of the two fundamental frequencies are different, the walk-off angles are not consistent, and the walk-off causes the two fundamental frequencies to be gradually separated. For the negative uniaxial crystal of which the fundamental frequency light comprises o light and e light, the II-type phase matching belonging to e + o → e, the positive uniaxial crystal of which the fundamental frequency light comprises o light and e light, and the II-type phase matching belonging to o + e → o obviously only when the fundamental frequency o light and the fundamental frequency e light coincide, the frequency doubling can occur. The walk-off causes the o light and the e light to be gradually separated, the frequency doubling efficiency is reduced, and when the o light and the e light are completely separated, the frequency doubling light is not generated any more. According to the traditional one-way nonlinear transformation through a nonlinear crystal, the separation degree of o light and e light is increased along with the increase of the propagation distance, but by adopting the nonlinear wavelength conversion structure with the full-reflection film, the walking-away direction of the reflected fundamental frequency light e light is opposite to the walking-away direction of the fundamental frequency light e light during incidence, so that the e light and the o light are gradually separated before reflection, the frequency doubling efficiency is reduced, the e light and the o light are gradually superposed after reflection, and the frequency doubling efficiency is improved.
Example 2
A laser nonlinear wavelength conversion system is structurally shown in FIG. 4 and comprises a third nonlinear crystal 13, a third dichroic mirror 33, a fourth dichroic mirror 34 and a second heat sink 42. The wavelengths of the fundamental frequency light used were 1064nm and 532 nm.
The third nonlinear crystal 13 is made of a negative biaxial LBO (lithium niobate) crystal, the double optical axes of the negative biaxial LBO crystal are arranged symmetrically about the z-axis, and the refractive indexes in the directions of the x, y and z axes are n respectivelyx、nyAnd nzSatisfy nz>ny>nxDue to the spherical coordinate system, the optimal phase matching angle theta of II-type phase matching of base frequency light of 1064nm and 532nm to base frequency light of 355nm and frequency light3=42.5 °, phi =90 °, and the optimal phase matching angle θ is set between the fundamental wave vector directions of 1064nm and 532nm incident perpendicularly to the surface of the third nonlinear crystal 13 and the z-axis direction of the negative biaxial LBO crystal3=42.5 °, phi =90 °, the third nonlinear crystal 13 is required to adopt a corner cut processing method similar to that of the first nonlinear crystal 11, that is, the processing corner cut of the negative biaxial LBO crystal is equal to the optimal phase matching angle θ3=42.5 °, Φ =90 °; one side of the third nonlinear crystal 13 is coated with 200 nm thick SiO2A protective film which polishes the surface; light is incident on the other surface of the third nonlinear crystal 13, and the incident end surface size is 10 × 10 mm, and the thickness is 3 mm.
The third dichroic mirror 33 and the fourth dichroic mirror 34 are located on the third non-linear crystal 13 without SiO plating2On one side of the protective film, the third dichroic mirror 33 is totally transmissive to the fundamental frequency light of 1064nm and totally reflective to the fundamental frequency light of 532nm, and the fourth dichroic mirror 34 is totally transmissive to the fundamental frequency light of 1064nm and 532nm and totally reflective to the sum frequency light of 355 nm.
One surface of the second heat sink 42 is sequentially plated with gold, titanium and SiO2Total reflection film (for total reflection of light at 1064nm, 532nm and 355 nm) and SiO2Then to the uppermost SiO layer2Polishing is performed to form a third nonlinear crystal 13 coated with SiO2One side of the protective film is polished with glue.
The 1064nm and 532nm fundamental frequency light respectively passes through the third dichroic mirror 33, is totally transmitted and totally reflected, then enters the fourth dichroic mirror 34, is totally transmitted by the fourth dichroic mirror 34, and then enters the third nonlinear crystal 13 to perform class II phase matching and frequency conversion from 1064nm, 532nm and 355 nm; the 1064nm and 532nm fundamental frequency light and the 355nm sum frequency light generated by the nonlinear conversion during the incidence are reflected by the total reflection film, the 1064nm and 532nm fundamental frequency light is subjected to frequency doubling continuously to generate 355nm sum frequency light, and the 355nm sum frequency light is emitted through the third nonlinear crystal 13 and then reflected by the fourth dichroic mirror 34.
The second heat sink 42 of the surface adhesive tape total reflection film on the third nonlinear crystal 13 has better heat dissipation effect than the traditional heat dissipation effect on the side surface of the nonlinear crystal, and can realize frequency doubling, sum frequency or difference frequency of the fundamental frequency light with large energy and high power.
For a biaxial crystal with fundamental frequency light containing two slow lights, the I-type phase matching belongs to e1+ e1 → e2, the generated sum frequency light is a fast light, the two fundamental frequency lights and the sum frequency light can both leave, and the leaving directions of the fast light and the slow light are on mutually perpendicular planes, when single fundamental frequency light is subjected to frequency doubling, the leaving can cause the change of the shape of a light spot, and when the two fundamental frequency lights are subjected to frequency summing, the leaving can also influence the efficiency; for the biaxial crystal of the embodiment in which the fundamental frequency light includes slow light (1064 nm) and fast light (532 nm), the class ii phase matching belongs to e1+ e2 → e2, the slow light and fast light in the fundamental frequency light are separated in mutually perpendicular planes, the slow light and fast light are gradually separated, the efficiency is reduced, and when the fundamental frequency slow light and fundamental frequency fast light are completely separated, the nonlinear effect will not occur any more. However, by adopting the nonlinear wavelength conversion structure with the total reflection film, the walk-off direction of the reflected fundamental frequency light is opposite to the walk-off direction of the incident fundamental frequency light, so that before reflection, the two fundamental frequency lights are gradually separated, the efficiency is reduced, after reflection, the two fundamental frequency lights are gradually superposed, and the efficiency is improved.

Claims (5)

1. A laser nonlinear wavelength conversion system is characterized by comprising a heat sink, a dichroic mirror and a surface coated with SiO2The laser comprises a nonlinear crystal of a protective film and a sapphire crystal with one surface plated with a total reflection film, wherein the total reflection film is used for reflecting fundamental frequency light and laser after nonlinear conversion; SiO of the nonlinear crystal2One side of the protective film is in optical cement with one side of the full-reflection film of the sapphire crystal, and the sapphire crystalThe other side of the gem crystal is welded with the heat sink; the dichroic mirror is positioned on the non-linear crystal and is not coated with SiO2One side of the protective film is used for separating the laser after the fundamental frequency light and the nonlinear conversion; the laser after nonlinear conversion is frequency doubling light, sum frequency light or difference frequency light.
2. The laser nonlinear wavelength conversion system according to claim 1, characterized in that a heat sink with one surface plated with a full-reflection film is adopted to replace a welded sapphire crystal and the heat sink; the total reflection film is used for reflecting the fundamental frequency light and the laser after nonlinear conversion, and the laser after nonlinear conversion is frequency doubling light, sum frequency light or difference frequency light.
3. The laser nonlinear wavelength conversion system of any one of claims 1 or 2, wherein the SiO2The thickness of the protective film is 50-200 nm.
4. The laser nonlinear wavelength conversion system in accordance with any one of claims 1 or 2, wherein the nonlinear crystal is a sheet-like crystal.
5. The laser nonlinear wavelength conversion system according to claim 2, wherein gold, titanium and first SiO are sequentially plated from a heat sink surface in the middle of the heat sink and the total reflection film2Layer and plating a second SiO on the other side of the total reflection film2And (3) a layer.
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Application publication date: 20211015