CN220382483U - High-power single-frequency extracavity five-time frequency laser - Google Patents

Abstract

The utility model relates to the field of laser, in particular to a design of the field of high-power single-frequency laser. Firstly, a high-power multi-end pump unidirectional circulation cavity is utilized to generate high-power single-frequency laser, secondly, the high-power single-frequency laser generates single-frequency double-triple-frequency laser output through intracavity frequency multiplication, and finally, a coupling optical path is arranged outside the circulation cavity to realize the sum frequency of the high-power single-frequency light, so that the high-power single-frequency five-time-frequency laser is generated. The structure of the utility model can easily obtain single-frequency five-time frequency laser of 1um laser wave band, and is widely applied to scene application requiring coherence length.

Description

High-power single-frequency extracavity five-time frequency laser

Technical Field

The utility model relates to the field of laser, in particular to a design in the field of high-power solid single frequency.

Background

The 210nm band deep ultraviolet light source has important application in the fields of semiconductor lithography, high-density storage, high-precision spectrum analysis and the like. Besides the characteristics of the common deep ultraviolet laser, the single-frequency deep ultraviolet laser has very good light source coherence, and can be widely applied to industries such as Raman spectrum, wafer detection, photoluminescence, high-stability micromachining and the like.

Disclosure of Invention

The utility model designs the high-power single-frequency extra-cavity five-time-frequency laser with simple structure and high reliability, and realizes the output of high-power single-frequency deep ultraviolet.

The utility model mainly comprises two parts in principle, wherein the first part is a high-power single-frequency generation system, and the second part is an extracavity single-frequency sum frequency system.

The high-power single-frequency generation system is characterized by comprising a full-reflection mirror (11), a coupling system I (201), a plano-convex dichroic mirror I (211), a laser crystal I (221), a plano-convex dichroic mirror II (212), a coupling system II (202), a plano-convex dichroic mirror I (131), a polarizing plate I (141), a magneto-optical crystal (15), a quarter wave plate (16), a polarizing plate II (142), an FP group (17), a frequency doubling crystal (18), a frequency tripler crystal (19), a plano-dichroic mirror II (132), a coupling system III (203), a plano-convex dichroic mirror III (213), a laser crystal II (222), a plano-convex dichroic mirror IV (214), a coupling system IV (204) and Q-switched light (12).

Wherein, the coupling system I (201), the coupling system II (202) is converged in the laser crystal I (221). And a coupling system III (203), wherein a coupling system IV (204) is converged in a laser crystal II (222). The pumping system adopts 878nm or 888nm pumping light, reduces the quantum defect of the laser crystal, and can generate higher pumping power. The corresponding laser crystal I (221), the laser crystal II (222) is doped neodymium particle crystal, the laser crystal length is about 50mm, the laser crystal is used for completely absorbing pump light, and the corresponding crystal concentration is adjusted according to design requirements.

The laser device comprises a first plano-convex dichroic mirror (211), a second plano-convex dichroic mirror (212), a third plano-convex dichroic mirror (213), and a fourth plano-convex dichroic mirror (214) which is a laser lens with a convex surface placed inwards, wherein the curvature of the lens and the coating requirement are determined according to design requirements, and the main purpose is to compensate the thermal focal length of crystals, so that high-power fundamental transverse mode laser output is realized.

The flat dichroic mirror I (131) and the flat dichroic mirror II (132) are low-pass high-reflection laser lenses, and mainly serve as folding and compressing optical paths for enabling fundamental frequency light to oscillate in a cavity and enabling high-order sum frequency light to be emitted, so that follow-up sum frequency is facilitated.

The combination of the first polaroid (141), the magneto-optical crystal (15), the quarter-wave plate (16) and the second polaroid (142) is a standard unidirectional circulating device, and the main purpose is to realize unidirectional laser circulation in a cavity and eliminate the space hole burning effect. The direction of propagation of the laser light in this combination is a unidirectional circulation from left to right in fig. 1 at the position of the first polarizer (141), the counter-propagating light is reflected out of the laser cavity through the first polarizer (141), and the laser light does not form an oscillation.

The FP group (17) is mainly used for realizing the frequency selection of a longitudinal mode, and one FP can be used for realizing the frequency selection, but the frequency control is unstable, and two FPs are used for realizing the frequency selection of an overlapping area of the two FPs so as to realize stable single-frequency output. Meanwhile, the FP group (17) is provided with a temperature control device, so that the influence of the external environment on the frequency of the laser is reduced.

The frequency doubling crystal (18), the frequency tripling crystal (19) is a device for converting single-frequency light into corresponding frequency doubling light output. All crystals are placed in a device using TEC for accurate temperature control for accurate control of the light output.

Wherein, Q-switch light (12) is used for realizing the adjustment of Q value and the output of pulse light.

The single frequency sum frequency system outside the cavity is characterized by comprising a flat dichroic mirror three (30), a reflecting mirror one (32), a coupling mirror one (35), a frequency doubling optical path system formed by a reflecting mirror two (31), a half wave plate (33), a coupling mirror two (34), a flat dichroic mirror four (36), a frequency doubling optical path system formed by a five-time frequency-doubling crystal (37), a beam splitting device (38) and a light blocking device (39).

The frequency doubling optical path system and the frequency tripling optical path system are characterized in that the propagation distances of the two paths are equal, and meanwhile, the focal points of the frequency doubling light also meet the coincidence relation.

The frequency doubling optical path system is characterized in that frequency doubling light is transmitted through a flat dichroic mirror III (30), is converged through a coupling mirror I (35) after changing the transmission direction through a reflecting mirror I (32), and is reflected into a five-time frequency-doubling crystal (37) through a flat dichroic mirror IV (36).

The triple-frequency optical path system is characterized in that triple-frequency light propagates through the third flat dichroic mirror (30) in a reflection mode, after the propagation direction is changed through the second flat dichroic mirror (31), the triple-frequency light after the propagation direction is changed is converged through the second coupling mirror (34) after the polarization state is changed through the second half wave plate (33), and finally enters the quintuple-frequency crystal (37) through the fourth flat dichroic mirror (36).

In the extracavity single-frequency sum frequency system, the flat dichroic mirror III (30) is a high-pass filter and is used for transmitting double-frequency light and reflecting triple-frequency light and for splitting light beams. And a four (36) flat dichroic mirror for beam combination is a low pass filter for double frequency light reflection, triple frequency light transmission, and beam combination for light beams.

Wherein, the half wave plate (33), the coupling mirror II (34) is plated with the frequency doubling antireflection film, and the coupling mirror I (35) is plated with the frequency doubling antireflection film. The incidence end face of the quintupling frequency crystal (37) can be plated with a double-triple frequency anti-reflection film, and the light emergent face is not plated with a film

Wherein the quintupling frequency crystal (37) is a deep ultraviolet sum frequency crystal, and a BBO crystal or a CLBO crystal is used.

Finally, the frequency-doubling light and the frequency-doubling light are split after passing through a beam splitting device (38) designed by a distribution angle, and if the frequency-doubling light is not used, a light blocking device (39) is needed for collecting the frequency-doubling light.

Drawings

Fig. 1 is a diagram of a correspondingly high power nanosecond extracavity five-fold laser.

Detailed Description

The utility model is described in further detail below with reference to the drawings and the specific examples. It should be understood that the specific examples described herein are intended to illustrate the utility model and are not intended to limit the utility model.

The system is integrally composed of two parts, namely a high-power single-frequency generation system and an extracavity single-frequency sum frequency system.

The first part of high-power single-frequency generation system is characterized in that the integral structure is the combination of two double-end pump plano-convex unstable cavities to realize high-power laser output, and meanwhile, a unidirectional circulating device, a frequency selecting device and a frequency doubling device are added in the cavities to realize the output of high-power single-frequency laser.

The full-reflection mirror (11), the first flat-convex dichroic mirror (211), the first laser crystal (221), the second flat-convex dichroic mirror (212), the first flat-convex dichroic mirror (131), the second flat-convex dichroic mirror (132), the third flat-convex dichroic mirror (213), the second laser crystal (222), the fourth flat-convex dichroic mirror (214) and the Q-switched light (12) form a circulating fundamental frequency resonant cavity. The first polaroid (141), the magneto-optical crystal (15), the quarter-wave plate (16) and the second polaroid (142) form a unidirectional circulating device, and laser circulates in the laser cavity from left to right at the position of the first polaroid (141) in the utility model. The FP group (17) is added on this basis mainly to achieve frequency selection in the longitudinal mode. Here, two FPs are used, and the two FP overlapping regions are frequency-selected to achieve a stable single frequency output. Meanwhile, the FP group (17) is provided with a temperature control device, so that the influence of the external environment on the frequency of the laser is reduced.

The total reflection mirror (11) is a monochromatic high reflection mirror, and a 1064nm wavelength single-point high reflection mirror is recommended in the utility model. A first plano-convex dichroic mirror (211), a second plano-convex dichroic mirror (212), a third plano-convex dichroic mirror (213) and a fourth plano-convex dichroic mirror (214), which are plano-convex low-pass high-reflection mirrors, and are recommended to use high-transmission 888nm laser, high-reflection 1064nm laser parameters, and reflection angles of less than 13 degrees.

The pumping source of the coupling system I (201), the coupling system II (202), the coupling system III (203) and the coupling system IV (204) recommends to use a 888nm laser pumping source, and the main advantage is that the quantum loss is small, less heat can be generated after Nd: YVO4 is passed, and the generation of intracavity frequency doubling light is facilitated.

Among them, the first laser crystal (221), the second laser crystal (222) and the Nd: YVO4 crystal are recommended, and the Nd: YVO4 crystal has the advantages of high conversion rate, laser polarization output and the like. The crystal is selected in various ways, the single pulse energy, the repetition frequency and the pumping parameters of the pumping source are selected comprehensively according to the use scene of a customer, the crystal is not limited to the YVO4 crystal, and the related 1um wave band neodymium ion laser crystal is within the protection scope of the utility model.

The first polaroid (141), the magneto-optical crystal (15), the quarter-wave plate (16) and the second polaroid (142) are standard unidirectional circulation devices, and mainly used for reducing the space hole burning effect and improving the single-frequency efficiency. In the utility model, the propagation direction of light is the propagation direction from the first polarizer (141) to the second polarizer (142), and the incident polarization direction and the emergent polarization direction are the same. Wherein the quarter wave plate (16) is a multi-stage wave plate with the recommended use wavelength of 1064nm, and the two sides are plated with high-transmittance films. The magneto-optical crystal (15) is recommended to use a magneto-optical crystal rotating 45 degrees at 1064nm polarized light, and the clear aperture is 3 times larger than the light spot size. Polarizer one (141) and polarizer two (142) recommend a corresponding polarization ratio greater than 500:1.

wherein the FP assembly (17) is mainly used for generating single-frequency laser output. In the design of the utility model, the FP group (17) consists of two FPs, and the purpose of the utility model is mainly to more finely select the frequency of laser. All FPs are placed in a temperature control device and used for precisely controlling the refractive index, so that the stability of frequency is realized.

Wherein, LBO is recommended to be used as a frequency doubling crystal by the frequency doubling crystal (18), but not limited to the LBO crystal, the crystal length is recommended to be longer than 20mm, and the coating modes are 1064nm and 532nm high transmittance. The TEC is used for precisely controlling the temperature of the LBO crystal, so that the purposes of high-efficiency frequency multiplication and tunable frequency multiplication power are achieved. LBO is recommended to be used as a sum frequency crystal by the frequency tripling crystal (19), but not limited to the LBO crystal, the crystal length is recommended to be longer than 20mm, the coating mode is 1064nm,532nm and 355nm high transmittance, and the advantage of using the LBO is that the walk-off is small, the beam quality is excellent, the damage resistance is high and the like.

The corresponding frequency multiplication process is that the unidirectional circulating laser propagates from left to right, frequency multiplication light is generated through the frequency doubling crystal (18), when the laser continues to propagate, frequency multiplication light and residual fundamental frequency light generate frequency tripling light in the frequency tripling crystal (19), and finally the frequency tripling light exits at the position of the flat dichroic mirror (132), and the residual fundamental frequency light continues to oscillate in the cavity.

Among them, the polarization direction and the crystal cutting direction are described below, and in the present utility model, it is recommended to use a first laser crystal (221), a second laser crystal (222) is a Nd: YVO4 crystal, the C-axis direction is parallel to the paper surface, and finally, the polarization direction of fundamental frequency light is parallel to the paper surface. The frequency doubling crystal (18) is an LBO crystal, fundamental frequency light is generated through frequency doubling crystal by using I-type phase matching, and the cutting direction of the crystal is theta=90; phi=10.8, the crystal is a normal temperature crystal, the frequency multiplication efficiency is precisely controlled by the TEC, and the polarization direction of the frequency multiplication light is vertical to the paper surface. The frequency tripled crystal (19) is an LBO crystal, and the fundamental frequency light and the frequency doubled light are generated at the frequency tripled light using II phase matching in the frequency tripled crystal (19). The cutting direction of the frequency tripled crystal is theta=44; phi=90, the temperature is 50 ℃ crystal, and the polarization direction of the frequency tripled after summation is parallel to the paper surface for the main purpose of preventing deliquescence. The light output power can be controlled by temperature control of the TEC, the power ratio of the frequency tripled light to the frequency doubled light which can be emitted under ideal conditions is 2:1, the frequency doubled light cannot be completely converted into the frequency tripled power due to the influence of a walk-off effect and the like, only a specific conversion ratio is needed, and finally the ratio of the frequency tripled light to the frequency doubled light is controlled to be 3:2 by adjusting the temperature control.

The single-frequency laser has relatively high sensitivity to temperature and disturbance, and the integral structure is arranged in a shell controlled by a high-precision water tank, and meanwhile, a temperature control device is arranged at a special position such as an FP group (17), a frequency doubling crystal (18) and a frequency tripling crystal (19) to prevent severe mode jump.

The single-frequency sum frequency system outside the cavity is characterized by comprising a flat dichroic mirror III (30), a reflecting mirror I (32), a frequency doubling optical path system formed by a coupling mirror I (35), a reflecting mirror II (31), a half wave plate (33), a coupling mirror II (34), a frequency tripler optical path system formed by a flat dichroic mirror IV (36), a frequency tripler crystal (37), a beam splitting device (38) and a light blocking device (39).

In an extracavity single-frequency sum frequency system, the main sum frequency mode is that the frequency of the frequency-quincuncial light is summed in a frequency-quincuncial crystal (37) through I-type phase matching to realize the output of the frequency-quincuncial light. Light of the second and third frequency multiplication emitted from the high-power single-frequency generating system is firstly incident on the flat-dichroic mirror III (30), the flat-dichroic mirror III (30) has the main functions of splitting the second and third frequency multiplication light, and a coating scheme is recommended to be 532nm high-transmittance, 355nm high-reflection and 45-degree reflection, namely a high-pass coating scheme.

After passing through the flat dichroic mirror three (30), the doubling frequency changes the propagation direction after passing through the mirror one (32), and then the light is converged by the coupling mirror one (35). The focal length of the coupling mirror one (35) is not particularly small, and the recommended distance is about 200mm, and then the coupling mirror one (35) is reflected by the flat dichroic mirror four (36) into the five-time frequency crystal (37).

The triple-frequency light reflected by the flat dichroic mirror three (30) is controlled in its propagation direction by the mirror two (31) and then passes through a half-wave plate (33), wherein the half-wave plate (33) is a half-wave plate of the triple-frequency light, and the optical axis direction and the polarization direction of the incident light are 45 DEG, so that the polarization direction of the incident light becomes perpendicular to the original direction after passing through the wave plate. The light after changing the polarization direction is then converged by a second coupling mirror (34), and the converged light enters the crystal by a fourth flat dichroic mirror (36), wherein the focal length of the second coupling mirror (34) and the focal length of the first coupling mirror (35) can be different.

The double frequency light and the triple frequency light are converged into a quintuple frequency crystal (37) after passing through the same flat dichroic mirror IV (36), and in the quintuple frequency crystal (37), I-type phase matching is used for generating quintuple frequency laser.

Wherein, when the sum frequency is carried out in the five-time frequency crystal (37), two points are required to be ensured, namely the coincidence of the sum frequency light in space and time.

The spatial coincidence of the two sum frequency lights is realized by respectively adjusting a first reflecting mirror (32), a fourth flat dichroic mirror (36) and a third flat dichroic mirror (30) in the light path of the frequency doubling light path, and a second reflecting mirror (31) is used for realizing the coincidence of the light paths of the frequency doubling light at the spatial position, and according to the definition of the spatial freedom degree, when two lenses in each light path can be freely adjusted, the direction of light transmission can be accurately controlled, so that the two lenses in the frequency doubling transmission light path can respectively adjust the own propagation direction, the coincidence of the spatial propagation directions can be satisfied, and simultaneously, the distance between the coupling mirror I (35) and the coupling mirror II (34) relative crystals can be adjusted, so that the two focuses coincide.

In addition, the two sum frequency lights also need to meet the requirement of superposition in time, namely, the optical path difference in the two optical paths is approximately zero, so that the time superposition can be met. Because the utility model is a nanosecond laser, the pulse width of the double frequency and triple frequency light of the laser is about 20ns according to the design of the front-stage laser, and the error of two light paths can generate essential influence on time coincidence only when reaching the level of more than 1 meter according to the calculation of the light speed. Therefore, the optical path distances after being separated are ensured to be equal as much as possible through ruler measurement, and the requirement of corresponding frequency doubling efficiency can be met.

The five-time frequency crystal (37) is simple to select, only BBO and CLBO can be used commercially by the crystal on the market, and BBO can be used as a deep ultraviolet excellent sum frequency crystal by comprehensively considering. BBO crystals have two major drawbacks that are unavoidable. Firstly, BBO crystals have a relatively large absorption effect on deep ultraviolet; secondly, the BBO crystals walk off more severely. In order to reduce the influence of the two defects of the BBO crystal on the quality of the light beam as much as possible, the beam shrinkage convergence is adopted to increase the corresponding frequency doubling efficiency. The focal length of the coupling mirror I (35) and the coupling mirror II (34) can be well controlled, and the light spot size in the crystal can be well controlled, so that the frequency doubling efficiency is properly improved. The length of the quintupling crystal (37) is calculated to recommend a crystal of not more than 6mm so that the crystal spot deformation can be relatively controlled.

The mixed deep ultraviolet laser is separated from incident light by a beam splitting device (38), and then the deep ultraviolet laser can be subjected to beam shaping if necessary to reduce astigmatism of the deep ultraviolet laser, but the beam shaping can reduce light output power, and finally the beam shaping is balanced according to the use condition.

The corresponding polarization direction and crystal cut direction are described. The frequency doubling and frequency tripled emitted from the laser cannot directly generate the five-time frequency deep ultraviolet light by frequency summation, and the polarization direction of the frequency tripled needs to be changed to meet the phase matching condition. The three-fold frequency light emitted as a whole is parallel to the paper surface, the polarization direction is changed to be perpendicular to the paper surface after passing through the half-wave plate (33), when the three-fold frequency light is incident into the five-fold frequency crystal (37), the two-fold frequency light and the three-fold frequency light are both perpendicular to the paper surface, and the five-fold frequency light after frequency conversion is parallel to the paper surface. After the five-fold frequency light parallel to the paper passes through the beam splitting device (38) with two cloth angles, the loss of deep ultraviolet light can be reduced as much as possible.

The cutting direction of the five-time frequency crystal (37) is theta=69.7 DEG, and phi=0 DEG, so that the BBO crystal is not very sensitive to temperature, and the excessive requirement on temperature is not needed during frequency summation. When the temperature of the frequency doubling and the frequency tripling of the laser is changed, the proportion of laser incident into the BBO crystal can be changed, and the temperature of the frequency doubling is finally determined by monitoring the emitted laser power of the frequency quintupling.

The foregoing is merely a preferred embodiment of the present utility model and it should be noted that modifications and adaptations to those skilled in the art may be made without departing from the principles of the present utility model, which are intended to be comprehended within the scope of the present utility model.

Claims (7)

1. The high-power single-frequency extracavity five-time frequency laser is characterized by comprising a high-power single-frequency generation system and an extracavity single-frequency sum-frequency system, wherein the high-power single-frequency generation system consists of a full-shot mirror (11), a coupling system I (201), a plano-convex dichroic mirror I (211), a laser crystal I (221), a plano-convex dichroic mirror II (212), a coupling system II (202), a plano-convex dichroic mirror I (131), a polaroid I (141), a magneto-optical crystal (15), a quarter wave plate (16), a polaroid II (142), an FP group (17), a frequency doubling crystal (18), a frequency tripling crystal (19), a plano-dichroic mirror II (132), a coupling system III (203), a plano-convex dichroic mirror III (213), a laser crystal II (222), a plano-convex dichroic mirror IV (214), a coupling system IV (204) and Q-switched light (12); the extracavity single-frequency sum frequency system consists of a flat dichroic mirror III (30), a reflecting mirror I (32), a coupling mirror I (35), a reflecting mirror II (31), a half-wave plate (33), a coupling mirror II (34), a flat dichroic mirror IV (36), a five-time frequency crystal (37), a beam splitting device (38) and a light blocking device (39).

2. The high-power single-frequency extracavity quintuple-frequency laser according to claim 1, comprising a high-power single-frequency generation system consisting of a full mirror (11), a coupling system one (201), a plano-convex dichroic mirror one (211), a laser crystal one (221), a plano-convex dichroic mirror two (212), a coupling system two (202), a plano-convex dichroic mirror one (131), a plano-convex dichroic mirror two (132), a coupling system three (203), a plano-convex dichroic mirror three (213), a laser crystal two (222), a plano-convex dichroic mirror four (214), a coupling system four (204), and a Q-switched light (12) constituting a high-power fundamental frequency cavity for generating a high-power fundamental-frequency transverse-mode laser.

3. The high-power single-frequency extracavity five-time frequency laser according to claim 1, comprising a high-power single-frequency generation system, wherein a coupling system one (201), a coupling system two (202), a coupling system three (203), a coupling system four (204) are four-end pump systems, and the four high-power pump systems use 878nm or 888nm pump light to generate higher pump power and lower thermal effect.

4. The high-power single-frequency extracavity five-time frequency laser according to claim 1, characterized by comprising a high-power single-frequency generation system in which FP groups (17) use two FPs to achieve single longitudinal mode output at high power by precise temperature control.

5. The high power single frequency extra-cavity five-times laser of claim 1 comprising an extra-cavity single frequency sum frequency system wherein the distance from flat dichroic mirror three (30), mirror one (32), flat dichroic mirror four (36), flat dichroic mirror three (30), mirror two (31), flat dichroic mirror four (36) is equal.

6. The high power single frequency extra-cavity five-fold laser of claim 1, comprising an extra-cavity single frequency sum frequency system in which the frequency-doubled light spatially coincides when entering the five-fold frequency crystal (37).

7. The high-power single-frequency extra-cavity quintuple-frequency laser according to claim 1, comprising an extra-cavity single-frequency sum-frequency system, wherein a half wave plate (33) in the extra-cavity single-frequency sum-frequency system is used for changing the polarization mode of the triplen light so that the polarization mode of the two triplen light finally incident on the quintuple-frequency crystal (37) is consistent.