CN1218448C

CN1218448C - Biperiod superlattice and its application in laser frequency converter

Info

Publication number: CN1218448C
Application number: CN00119006.7A
Authority: CN
Inventors: 朱永元; 祝世宁; 秦亦强; 刘照伟; 刘辉; 王惠田; 何京良; 闵乃本
Original assignee: Nanjing University
Current assignee: Nanjing University
Priority date: 2000-10-11
Filing date: 2000-10-11
Publication date: 2005-09-07
Anticipated expiration: 2020-10-11
Also published as: CN1288275A

Abstract

The present invention relates to a double-cycle superlattice and application thereof in laser frequency conversion. A ferroelectric crystal is used as a substrate by the kind of superlattice, and two reciprocal lattice vectors used for matching wave vector mismatch of frequency multiplication and frequency summing can be simultaneously provided by the arrangement of a specific double-modulation structure so that frequency tripling can be continuously increased. Thus, frequency tripling with high efficiency is realized, or the simultaneous output of frequency multiplication and frequency tripling is realized. A potassium tantalate (LiTaO3) superlattice with the kind of structure can be used for tripling frequency for 1064 nanometer lasers of an Nd: YVO4 laser device and an Nd: YAG laser device so as to output ultraviolet lasers of 355 nanometers.

Description

Superlattice with double period structure and its application in laser frequency conversion

技术领域technical field

本发明涉及一种双周期调制结构的超晶格设置，以及这种双周期超晶格在激光变频中的应用，这种超晶格具有直接三倍频的功能。The invention relates to a superlattice arrangement of a double-period modulation structure, and the application of the double-period superlattice in laser frequency conversion. The superlattice has the function of direct triple frequency.

背景技术Background technique

祝世宁等人1997年在science上发表了“用准周期Fibonacci光学超晶格(QPOS)实现绿光三倍频”的文章(S.N.Zhu，Yong-yuan Zhu，N.B.MingQuasi-Phase-Matched Third Harmonic Generation in a Quasi-Periodic OpticalSuperlattice Science 278，843(1997))。利用准周期Fibonacci序列的LiTaO_3-(钽酸锂)超晶格，三倍频1570nm的Nd:YAG激光，产生523nm的绿光。QPOS的基本参数1＝10.7μm，A＝24μm，B＝17.5μm。样品总长度为8mm，厚度为0.5mm。1570nm红外光单次通过QPOS三倍频，产生绿光功率达6mW，转换效率为23％。Zhu Shining and others published the article "Using Quasi-Periodic Fibonacci Optical Superlattice (QPOS) to Realize Green Light Tripling" in Science in 1997 (SNZhu, Yong-yuan Zhu, NBMingQuasi-Phase-Matched Third Harmonic Generation in a Quasi - Periodic Optical Superlattice Science 278, 843 (1997)). Using the quasi-periodic Fibonacci sequence LiTaO _3- (lithium tantalate) superlattice, triple the frequency of 1570nm Nd:YAG laser to generate 523nm green light. Basic parameters of QPOS 1 = 10.7 μm, A = 24 μm, B = 17.5 μm. The sample has a total length of 8 mm and a thickness of 0.5 mm. 1570nm infrared light is tripled by QPOS in a single pass to generate green light with a power of 6mW and a conversion efficiency of 23%.

J.P.Meyn和M.M.Fejer在1997年的Opt.lett上发表了“利用周期极化的钽酸锂通过二倍频获得紫外输出”(Meyn J.P，Fejer MM Tunable ultraviolet-radiation by second-harmonic generation in periodically poled lithiumtantalate，PT LETT 22(16)：1214-1216 AUG 15 1997)的文章。钽酸锂(LiTaO_3-)或铌酸锂(LiNbO₃)超晶格的周期为2.625μm，获得的的紫外激光的波长是325nm，其有效非线性系数为2.6pm/V，是理论值的55％。JPMeyn and MMFejer published on Opt.lett in 1997 "Using periodically poled lithium tantalate to obtain ultraviolet output through double frequency" (Meyn JP, Fejer MM Tunable ultraviolet-radiation by second-harmonic generation in periodically poled lithiumtantalate, PT LETT 22(16):1214-1216 AUG 15 1997). The period of lithium tantalate (LiTaO _3- ) or lithium niobate (LiNbO ₃ ) superlattice is 2.625μm, the wavelength of the obtained ultraviolet laser is 325nm, and its effective nonlinear coefficient is 2.6pm/V, which is the theoretical value 55%.

A.Arie等人在Optics Communications上发表了“用周期极化的KTP(磷酸钛氢钾)准位相匹配产生倍频绿光和紫外光”的文章(Arie A，Rosenman G，MahalV，et al.Green and ultraviolet quasi-phase-matched second harmonicgeneration in bulk periodically-poled KTiOPO4 OPT COMMUN 142(4-6)：265-268OCT 15 1997)，利用一块周期为8.98μm的KTP超晶格实现的对783.5nm激光的倍频紫外输出，1厘米长的超晶格晶体，泵浦光为259mW时，可得到75.3μW的紫外激光，转换效率为0.12％/W.A.Arie et al. published the article "Using Periodically Polarized KTP (Potassium Titanium Hydrogen Phosphate) Potential Matching to Generate Frequency Doubled Green Light and Ultraviolet Light" on Optics Communications (Arie A, Rosenman G, MahalV, et al. Green and ultraviolet quasi-phase-matched second harmonic generation in bulk periodically-poled KTiOPO4 OPT COMMUN 142(4-6): 265-268OCT 15 1997), using a KTP superlattice with a period of 8.98μm to realize the 783.5nm laser Frequency doubled ultraviolet output, 1 cm long superlattice crystal, when the pump light is 259mW, it can get 75.3μW ultraviolet laser, and the conversion efficiency is 0.12%/W.

以上三篇文章分别介绍了用准周期光学超晶格实现绿光三倍频和用周期光学超晶格实现激光紫外倍频。在第一篇文章中，使用的是标准Fibonacci的准周期超晶格。第二篇文章和第三篇文章分别是用周期超晶格对650nm和783.5nm光源倍频实现紫外激光输出。所有上述方案均不涉及双调制结构超晶格和利用该结构的超晶格实现激光三倍频，不涉及对1064nm激光进行直接三倍频获得355nm紫外激光。The above three articles respectively introduce the frequency doubling of green light by quasi-periodic optical superlattice and the frequency doubling of laser ultraviolet light by using periodic optical superlattice. In the first article, a standard Fibonacci quasi-periodic superlattice is used. The second article and the third article respectively use periodic superlattice to double the frequency of 650nm and 783.5nm light sources to realize ultraviolet laser output. All the above schemes do not involve double modulation structure superlattice and using the superlattice to achieve laser triple frequency, and do not involve direct triple frequency of 1064nm laser to obtain 355nm ultraviolet laser.

发明内容Contents of the invention

本发明的目的在于寻找一种新型光学超晶格设置结构——双调制结构，该结构能实现多波长激光倍频和对任何波长的激光三倍频。从而提供一种光学超晶格晶体作为三倍频频率转换器件，构成一种高效率的小型全固态的能够输出绿光、蓝光、紫光或近紫外的激光器。特别是采用一块双周期结构的LiTaO₃超晶格对Nd:YVO₁和Nd:YAG激光器1064nm输出直接三倍频，获得355纳米的紫外激光输出。The purpose of the present invention is to find a novel optical superlattice setting structure—double modulation structure, which can realize frequency doubling of multi-wavelength laser and triple frequency of laser of any wavelength. Therefore, an optical superlattice crystal is provided as a triple frequency conversion device to form a high-efficiency small all-solid-state laser capable of outputting green light, blue light, purple light or near ultraviolet light. In particular, a LiTaO ₃ superlattice with a double-period structure is used to directly triple the frequency of the 1064nm output of the Nd:YVO ₁ and Nd:YAG lasers to obtain a 355nm ultraviolet laser output.

本发明目的是这样实现的：利用一块双调制(双周期或周期——准周期)结构的钽酸锂LiTaO₃、铌酸锂LiNbO₃、磷酸钛氧钾KTP超晶格作为激光变频介质，其特征在于：这种双调制结构能够同时提供用来匹配倍频和和频波矢失配的二个倒格矢，从而使三倍频能够持续的增长，实现高效的三倍频输出。由于该结构的倒格矢的位置和大小可通过对结构参数设置进行调节，从而可以实现任意波段尤其是蓝光、近紫外和紫外的激光高效三倍频。The purpose of the present invention is achieved in this way: a piece of lithium tantalate LiTaO ₃ , lithium niobate LiNbO ₃ , potassium titanyl phosphate KTP superlattice with a double modulation (double period or period—quasi-period) structure is used as the laser frequency conversion medium. The characteristic lies in that the double modulation structure can simultaneously provide two reciprocal lattice vectors for matching the mismatch of the multiplier and sum frequency wave vectors, so that the triple frequency can continuously increase and realize efficient triple frequency output. Since the position and size of the reciprocal vector of the structure can be adjusted by setting the structure parameters, it is possible to realize efficient triple frequency-tripping of lasers in any wavelength band, especially blue light, near ultraviolet and ultraviolet.

现以双周期超晶格为例说明这种双调制结构超晶格的设置过程：Now take the double-period superlattice as an example to illustrate the setting process of this double-modulation structure superlattice:

基本思路是对于任意的基波波长，选取其周期结构参数使结构中倍频过程及和频过程产生的波矢失配大小相等，在这种情况下，二次谐波输出是等振幅或变振幅振荡的。三次谐波输出是在轻微振荡中增长的。二次谐波三次谐波的强度随周期超晶格晶体长度的关系见图3所示，这样，以二次谐波输出的振荡周期为新的周期对原周期结构进行再次调制。其结果是二次谐波得到持续增长，导致三次谐波光也能够高效输出。基波、倍频和三倍频的强度随双周期超晶格晶体的关系如图4所示(周期——准周期超晶格的设置思想与方法同)。图1和图2是其中一种双周期设置方案的模板和频谱。The basic idea is that for any fundamental wavelength, select its periodic structure parameters so that the wave vector mismatches generated by the frequency doubling process and the sum frequency process in the structure are equal in size. In this case, the second harmonic output is of equal amplitude or variable Oscillating in amplitude. The third harmonic output grows in slight oscillations. The relationship between the strength of the second harmonic and the third harmonic and the length of the periodic superlattice crystal is shown in Figure 3. In this way, the original periodic structure is re-modulated with the oscillation period output by the second harmonic as the new period. The result is a continuous increase in the second harmonic, resulting in efficient output of third harmonic light as well. The relationship between the intensity of the fundamental wave, double frequency and triple frequency with the dual-period superlattice crystal is shown in Figure 4 (the idea and method of period-quasi-periodic superlattice setting are the same). Figures 1 and 2 are the template and spectrum for one of the two-cycle setup schemes.

在图1中我们看到，双周期的主要参数是小的周期结构的周期l和大的调制周期结构L。如果这两个参数确定了，双周期结构基本上就确定了。下面我们看看如何通过设置的要求来导出这两个基本参数。In Fig. 1 we see that the main parameters of the double period are the period l of the small periodic structure and the large modulation periodic structure L. If these two parameters are determined, the double-period structure is basically determined. Let's see how to derive these two basic parameters through the set requirements.

图2是双周期结构的典型频谱图。我们用Gm，n来表示这种双周期结构的主要倒格矢，m、n是整数：Figure 2 is a typical spectrum diagram of a double-period structure. We use Gm,n to denote the main reciprocal vector of this double period structure, m, n are integers:

$Gm G m,, n no = = \frac{22 πm πm}{l l} + + \frac{22 πn πn}{L L} \cdot \cdot \cdot &Center Dot; \cdot &Center Dot; \cdot \cdot \cdot \cdot \cdot \cdot ((11))$

ΔK₁，ΔK₂分别代表倍频及和频过程中的波矢失配，如果我们选择双周期结构中的Gm，n和Gm′，n′分别来补偿这两个波矢失配，则有ΔK ₁ , ΔK ₂ represent the wave vector mismatch in the multiplication and sum frequency process respectively. If we choose Gm, n and Gm′, n′ in the double-period structure to compensate these two wave vector mismatches respectively, then we have

$Gm G m,, n no - - Δ Δ {K K}_{11} = = \frac{22 πm πm}{l l} + + \frac{22 πn πn}{L L} - - Δ Δ {K K}_{11} = = 00$

$G G {m m}^{' '},, {n no}^{' '} - - Δ Δ {K K}_{22} = = \frac{22 {πm πm}^{' '}}{l l} + + \frac{22 {πn πn}^{' '}}{L L} - - Δ Δ {K K}_{22} = = 00 \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot; \cdot &Center Dot; \cdot \cdot ((22))$

由以上公式我们可求出双周期的主要结构参数l和L的表达式：From the above formulas, we can obtain the expressions of the main structural parameters l and L of the double period:

$l l = = \frac{22 π π (({mn mn}^{' '} - - {m m}^{' '} n no))}{Δ Δ {k k}_{11} {n no}^{' '} - - {Δk Δ k}_{22} n no}$

$L L = = \frac{22 π π (({nm nm}^{' '} - - {n no}^{' '} m m))}{Δ Δ {k k}_{11} {m m}^{' '} - - {Δk Δk}_{22} m m}$

................(3) ...................(3)

其中的Δk₁，Δk₂又可表示为：Among them, Δk ₁ and Δk ₂ can be expressed as:

${Δk Δ k}_{11} = = \frac{44 π π}{λ λ} (({n no}_{22} - - {n no}_{11}))$

$Δ Δ {k k}_{22} = = \frac{22 π π}{λ λ} (({33 n no}_{33} - - {22 n no}_{22} - - {n no}_{11}))$

................(4) ...................(4)

(4)式中的n₁，n₂，n₃分别是超晶格晶体在基波，二倍频，三倍频时的折射率。一般情况下，选择m＝1，n＝-1，m’＝3，n’＝1(图1，图2就是这种情况)。如果以最常用的Nd激光器的1064nm输出为基波，设置温度为40℃，双周期结构的两个基本参数l＝6.77um，L＝50.86um(对LiTaO₃而言)。n ₁ , n ₂ , and n ₃ in formula (4) are the refractive indices of the superlattice crystal at fundamental wave, double frequency, and triple frequency respectively. In general, select m=1, n=-1, m'=3, n'=1 (this is the case in Fig. 1 and Fig. 2). If the 1064nm output of the most commonly used Nd laser is used as the fundamental wave and the temperature is set at 40°C, the two basic parameters of the double-period structure are l=6.77um and L=50.86um (for LiTaO ₃ ).

在具体的设置中，一组用来匹配倍频失配和和频失配的两个倒格矢可作灵活选择。可选择G_1，-1，G_3，1或者G_1，-1，G_3，-1或者G_1，-3，G_3，-1，不同的选择导致不同的双周期结构，对应于不同的基波波长。In a specific setting, a set of two reciprocal lattice vectors for matching octave mismatch and sum frequency mismatch can be flexibly selected. G _{1, -1} , G _3, 1 or G _{1, -1} , G _{3, -1} or G _{1, -3} , G _{3, -1} can be selected, different choices lead to different double period structures, corresponding to different the fundamental wavelength.

因为紫外、近紫外光已靠近LiTaO₃晶体的吸收边，实际三倍频的转换效率要比理论计算的略小。同时，为了消除光折变效应对转换效率和光斑质量的影响，设置的匹配温度最好在100℃～200℃之间。Because the ultraviolet and near-ultraviolet light is close to the absorption edge of the LiTaO ₃ crystal, the conversion efficiency of the actual triple frequency is slightly smaller than the theoretical calculation. At the same time, in order to eliminate the influence of the photorefractive effect on the conversion efficiency and the quality of the light spot, it is best to set the matching temperature between 100°C and 200°C.

这种双周期结构的超晶格可用铁电晶体材料，如LiTaO₃，LiNbO₃，KTP等，通过室温极化或条纹生长法来制备，结合波导工艺也可以制备成具有同样频率转换功能的双调制畴结构光波导器件。即LT、LN或KPT超晶格作为激光变频介质。The superlattice with double-period structure can be prepared by ferroelectric crystal materials, such as LiTaO ₃ , LiNbO ₃ , KTP, etc., by room temperature polarization or stripe growth method, combined with waveguide technology can also be prepared into a dual Modulating Domain Structured Optical Waveguide Devices. That is, LT, LN or KPT superlattice is used as the laser frequency conversion medium.

在材料设置中需要利用材料折射率的色散公式，这里给出LiTaO₃单晶的含温度系数的色散公式：In the material setting, the dispersion formula of the refractive index of the material needs to be used. Here is the dispersion formula of LiTaO ₃ single crystal with temperature coefficient:

${n no}_{e e}^{22} ((λ λ,, T T)) = = A A + + \frac{B B + + b b ((T T))}{{{λ λ}^{22} - - [[C C + + c c ((T T))]]}^{22}} + + \frac{E E.}{{λ λ}^{22} - - {F f}^{22}} + + {Dλ Dλ}^{22}$

其中的参数为：The parameters are:

A＝4.5284，B＝7.2449×10^-3，C＝0.2453，D＝-2.3670×10^-2，A=4.5284, B=7.2449×10 ^-3 , C=0.2453, D=-2.3670×10 ^-2 ,

E＝7.7690×10^-2，F＝0.1838，b(T)＝2.6794×10^-8(T+273.15)²，E=7.7690×10 ^-2 , F=0.1838, b(T)=2.6794×10 ^-8 (T+273.15) ² ,

c(T)＝1.6234×10^-8(T+273.15)².c(T)＝1.6234×10 ^-8 (T+273.15) ² .

对其他材料如LiNbO₃，KTP等请参阅非线性光学材料手册和有关文献。For other materials such as LiNbO ₃ , KTP, etc., please refer to the Handbook of Nonlinear Optical Materials and related literature.

本发明的特点是：本发明用光学超晶格晶体代替常规使用的非线性光学晶体，用双调制结构光学超晶格代替周期、准周期结构光学超晶格，从而可对任何激光波长实现直接三倍频。由于LiTaO₃紫外吸收边在280纳米，采用一块双周期结构的LiTaO₃超晶格可实现对最普及的Nd激光器1064纳米输出的直接三倍频，获得355纳米的紫外输出。和半导体激光器相结合，可研制成低阈值、高效率、优质光束、结构简单和小型全固态紫外激光器。因而在光谱学，生物医学，生物医药研究，光信息储存及其他领域得将到广泛的应用。The characteristics of the present invention are: the present invention replaces conventionally used nonlinear optical crystals with optical superlattice crystals, and replaces periodic and quasi-periodic optical superlattices with dual modulation optical superlattices, so that any laser wavelength can be directly Triple frequency. Since the UV absorption edge of LiTaO ₃ is at 280 nm, a LiTaO ₃ superlattice with a double-period structure can directly triple the frequency of the most popular Nd laser output at 1064 nm, and obtain a UV output of 355 nm. Combined with a semiconductor laser, it can be developed into a low-threshold, high-efficiency, high-quality beam, simple structure and small all-solid-state ultraviolet laser. Therefore, it will be widely used in spectroscopy, biomedicine, biomedical research, optical information storage and other fields.

附图说明：Description of drawings:

下面结合附图及具体实施方案对本发明作进一步详细说明：Below in conjunction with accompanying drawing and specific embodiment the present invention is described in further detail:

图1为本发明的一种双周期设置方案的模板示意图Fig. 1 is the template schematic diagram of a kind of two-period setting scheme of the present invention

图2是双周期结构的典型频谱图，横座标为倒格矢，纵座标为傅立叶系数值Figure 2 is a typical spectrogram of a double-period structure, the abscissa is the reciprocal vector, and the ordinate is the Fourier coefficient value

图3所示为二次谐波、三次谐波的强度随周期超晶格晶体长度的关系图。三倍频效率随着晶体横轴的长度增加而增加。以二次谐波输出的振荡周期为新的周期对原周期结构进行再次调制。其结果是二次谐波得到持续增长，导致三次谐波光也能够高效输出。Fig. 3 is a graph showing the relationship between the intensity of the second harmonic and the third harmonic and the length of the periodic superlattice crystal. The triple frequency efficiency increases with the length of the transverse axis of the crystal. The original periodic structure is re-modulated with the oscillation period of the second harmonic output as the new period. The result is a continuous increase in the second harmonic, resulting in efficient output of third harmonic light as well.

图4为基波、倍频和三倍频的强度随双周期超晶格晶体长度的关系图，其中纵座标表示转换效率，而FG、SHG、THG三根曲线分别表示基波、倍频和三倍频的转换效率，横座标为长度。Figure 4 is the relationship diagram of the intensity of the fundamental wave, double frequency and triple frequency with the length of the double-period superlattice crystal, where the ordinate represents the conversion efficiency, and the three curves of FG, SHG and THG respectively represent the fundamental wave, frequency double and The conversion efficiency of triple frequency, the abscissa is the length.

图5是本发明的紫外、近紫外激光器的结构示意图。Fig. 5 is a schematic structural view of the ultraviolet and near ultraviolet lasers of the present invention.

图6是本发明的紫外、近紫外激光器的一种镀膜设置的结构示意图。FIG. 6 is a schematic structural view of a coating arrangement for ultraviolet and near-ultraviolet lasers of the present invention.

图7是本发明的紫外、近紫外激光器的一种加腔设置的结构示意图。Fig. 7 is a schematic structural view of a cavity-added arrangement of the ultraviolet and near-ultraviolet lasers of the present invention.

图面说明如下：The illustrations are as follows:

1-LD激光器，波长为808nm；2-聚焦系统，一般为透镜组；1-LD laser with a wavelength of 808nm; 2-focusing system, usually a lens group;

3-Nd:YVO₄晶体，产生1064nm激光的激光介质；3-Nd: YVO ₄ crystal, the laser medium that produces 1064nm laser;

4-调Q装置(如声光装置)；5-1064nm激光的输出镜(如T＝20％)；4-Q-switching device (such as acousto-optic device); output mirror of 5-1064nm laser (such as T=20%);

6-会聚透镜(如f＝50mm)；7-控温炉，用来调节温度；6-converging lens (such as f=50mm); 7-temperature control furnace, used for regulating temperature;

8-双周期超晶格晶体，产生倍频黄绿光，三倍频紫外、近紫外激光；8-Double-period superlattice crystals, which produce double-frequency yellow-green light, triple-frequency ultraviolet and near-ultraviolet lasers;

9-输出的紫外、近紫外激光，或者黄绿，紫外双色激光；9-Output ultraviolet, near-ultraviolet laser, or yellow-green, ultraviolet two-color laser;

10-多层膜，1064nm的增透膜，532nm的高反膜；10-multilayer coating, 1064nm anti-reflection coating, 532nm high reflection coating;

11-532nm的高反膜，355nm的高透膜；11-532nm high reflective film, 355nm high transparent film;

12-谐振腔镜，为多色镜；12-resonant cavity mirror, which is a polychromatic mirror;

13-输出端腔镜，紫外、近紫外透光13-Cavity mirror at the output end, ultraviolet and near ultraviolet light transmission

具体实施方式：Detailed ways:

实施例1Example 1

按照图5制作一台用一块双周期超晶格组成的腔外三倍频近紫外激光器。1为808纳米的LD激光器，最大输出功率为15W，Nd:YVO₄晶体3的前表面镀膜，和腔镜5一起构成激光的谐振腔，在腔镜5后能产生大约2W的准连续1064纳米的激光。一块大小周期(L，l)分别为50.86微米和6.77微米的双周期钽酸锂超晶格(放置在控温炉(7)中，调节控温炉到45.4摄氏度时，产生波长为355纳米的紫外激光(9)。改变光学超晶格(8)的长度可改变输出紫外激光(9)的强度，一般超晶格的长度范围在几个毫米到几个厘米。According to Figure 5, an extra-cavity triple frequency near-ultraviolet laser composed of a double-period superlattice is fabricated. 1 is an 808nm LD laser with a maximum output power of 15W. The front surface of the Nd:YVO ₄ crystal 3 is coated, and together with the cavity mirror 5, it forms a laser resonant cavity. After the cavity mirror 5, it can generate about 2W of quasi-continuous 1064nm laser. A piece of double-period lithium tantalate superlattice (placed in a temperature-controlled furnace (7) with a size period (L, l) of 50.86 microns and 6.77 microns, when the temperature-controlled furnace is adjusted to 45.4 degrees Celsius, produces a wavelength of 355 nanometers Ultraviolet laser (9). Changing the length of the optical superlattice (8) can change the output intensity of the ultraviolet laser (9), and generally the length of the superlattice ranges from several millimeters to several centimeters.

实施例2Example 2

按照图6制作一台用一块双周期超晶格组成的三倍频近紫外激光器。与图5设置方案不同的是，在超晶格的前后两个表面进行镀膜处理。前表面镀1064纳米的增透膜，532纳米的高反膜；后表面镀532纳米的高反膜，355纳米的高透膜。这样在超晶格内部实现倍频532纳米激光的谐振，使其达到一定的强度，后表面532纳米高反膜的透过率可以调节输出绿光的强度。由于在超晶格内倍频激光强度的提高，三倍频紫外光的效率将明显提高，同时腔镜在不同波段透过率的调节可以实现输出绿光和紫外光的不同配比。According to Figure 6, a three-frequency near-ultraviolet laser composed of a double-period superlattice is fabricated. The difference from the setting scheme shown in Fig. 5 is that coating treatment is performed on the front and rear surfaces of the superlattice. The front surface is coated with a 1064nm antireflection coating and a 532nm high reflection coating; the rear surface is coated with a 532nm high reflection coating and a 355nm high transmission coating. In this way, the resonance of the frequency-doubled 532nm laser is realized inside the superlattice, making it reach a certain intensity, and the transmittance of the 532nm high-reflection film on the rear surface can adjust the intensity of the output green light. Due to the increase in the intensity of the frequency-doubled laser in the superlattice, the efficiency of the frequency-tripled ultraviolet light will be significantly improved. At the same time, the adjustment of the transmittance of the cavity mirror in different bands can achieve different ratios of output green light and ultraviolet light.

实施例3，按照图7制作一台用一块双周期超晶格组成的加腔三倍频近紫外激光器。将一块大小周期(L，l)分别为50.86微米和6.77微米的双周期钽酸锂超晶格8放置在谐振腔内，反射镜12为多色镜，透过1064nm的泵浦光而全反532nm的倍频光，腔镜13透过355nm的紫外光，而对532nm的透过率可按照需要进行调节。同实施例2一样，可同时实现倍频绿光和三倍频紫外的双色输出，它们之间的强度也可由腔镜在不同波段的透过率加以调节，而光束质量又大有改善。Embodiment 3, according to FIG. 7, a cavity-added triple-frequency near-ultraviolet laser composed of a double-period superlattice is fabricated. A double-period lithium tantalate superlattice 8 with a period (L, l) of 50.86 microns and 6.77 microns is placed in the resonator, and the mirror 12 is a polychromatic mirror, which is fully reflected by the 1064nm pump light For 532nm frequency-doubled light, the cavity mirror 13 transmits 355nm ultraviolet light, and the transmittance of 532nm can be adjusted as required. Same as Example 2, the two-color output of frequency-doubled green light and triple-frequency ultraviolet can be realized at the same time, and the intensity between them can also be adjusted by the transmittance of the cavity mirror in different wavelength bands, and the beam quality is greatly improved.

Claims

1. A superlattice material with a double-period structure, which is characterized by using ferroelectric crystal materials LiTaO ₃ , LiNbO ₃ , and KTP to prepare by room temperature polarization or stripe growth method, or combined with waveguide technology to prepare materials with the following structural parameters, Use Gm, n to represent the principal reciprocal lattice vector of this double period structure, m, n are integers:

Gm G m,, n no = = \frac{22 πm πm}{l l} + + \frac{22 πn πn}{L L}

ΔK ₁ and ΔK ₂ can represent the wave vector mismatch in the process of frequency doubling and sum frequency, and the superlattice materials Gm, n and Gm′, n′ of the dual-period structure are selected to compensate the two wave vector mismatches respectively, then there is

Gm G m,, n no - - Δ Δ {K K}_{11} = = \frac{22 πm πm}{l l} + + \frac{22 πn πn}{L L} - - {ΔK ΔK}_{11} = = 00

{Gm G m}^{' '},, {n no}^{' '} - - {ΔK ΔK}_{22} = = \frac{22 πm πm}{l l} + + \frac{22 πn πn}{L L} - - {ΔK ΔK}_{22} = = 00

Gm, n and Gm', n' are used to compensate the two wave vector mismatches respectively, thus the expressions of 1 and L of the main structure parameters of the double period are obtained:

l l = = \frac{22 π π (({mn mn}^{' '} - - {nm nm}^{' '}))}{{ΔK ΔK}_{11} {n no}^{' '} - - {Δk Δk}_{22} n no}

L L = = \frac{22 π π (({m m}^{' '} n no - - {n no}^{' '} m m))}{{ΔK ΔK}_{11} {m m}^{' '} - - {Δk Δk}_{22} m m}

{Δk Δk}_{11} = = \frac{44 π π}{λ λ} (({n no}_{22} - - {n no}_{11})),, {Δk Δk}_{22} = = \frac{22 π π}{λ λ} (({33 n no}_{33} - - {22 n no}_{22} - - {n no}_{11}))

In the above formula, n ₁ , n ₂ , and n ₃ are the refractive indices of the superlattice crystal at fundamental wave, double frequency, and triple frequency respectively.

2, by the superlattice material of double-period structure described in claim 1, it is characterized in that one group is used for matching frequency multiplier mismatch and sum frequency mismatch two reciprocal lattice arrows are flexibly selected, can select G _{1,- 1'} G _3,1 or G _1,-1' G _3,-1 or G _1,-3' G _3,-1' get different double periodic structures, corresponding to different fundamental wavelengths.

3. The application of double-period superlattice in laser frequency conversion is characterized by the use of a double-modulated or double-period structure of LiNbO ₃ , the expression of 1 and L of the main structural parameters of KTP double-period:

l l = = \frac{22 π π (({mn mn}^{' '} - - {nm nm}^{' '}))}{{ΔK ΔK}_{11} {n no}^{' '} - - {Δk Δk}_{22} n no}

L L = = \frac{22 π π (({m m}^{' '} n no - - {n no}^{' '} m m))}{{ΔK ΔK}_{11} {m m}^{' '} - - {Δk Δk}_{22} m m}

{Δk Δk}_{11} = = \frac{44 π π}{λ λ} (({n no}_{22} - - {n no}_{11})) {,, Δk Δk}_{22} = = \frac{22 π π}{λ λ} ((33 {n no}_{33} - - 22 {n no}_{22} - - {n no}_{11}))