可调谐钛宝石激光抽运的KTP单谐振光学参量振荡器的研究

介绍了 70 0nm～ 980nm的脉冲可调谐钛宝石激光抽运的KTP单谐振光学参量振荡器。通过改变抽运光波长作为光学参量振荡器输出参量光的调谐方式 ,确定了KTP晶体最佳切割角度 (θ=6 2 .5°,φ =0°) ,实验上获得了 12 5 1nm～ 2 5 32nm的连续参量光输出 ,最大输出能量约为 2 7 2mJ,最大转换效率为 35 7% (1311nm处 )。     

低阈值单谐振周期极化掺镁铌酸锂光参量振荡器

对基于周期极化掺镁铌酸锂晶体的信号光单谐振光学参量振荡器的输出特性进行了实验研究.讨论了光学参量振荡器谐振腔的腔长、周期极化铌酸锂晶体的通光长度、输出镜的透过率以及抽运光的脉冲宽度对光学参量振荡器谐振阈值的影响.光学参量振荡器的抽运源采用输出波长为1 064 nm的声光调Q Nd∶YVO4激光器,在重复频率为2 kHz、周期极化掺镁铌酸锂晶体的温度为30 ℃的条件下,光学参量振荡器的振荡阈值仅为48 mW.当抽运功率为94 mW时获得了25 mW的信号光输出,其光-光转换效率为26.6%.     

低阈值单谐振周期极化掺镁铌酸锂光参量振荡器

对基于周期极化掺镬铌酸锂晶体的信号光单谐振光学参量振荡器的输出特性进行了实验研究.讨论了光学参量振荡器谐振腔的腔长、周期极化铌酸锂晶体的通光长度、输出镜的透过率以及抽运光的脉冲宽度对光学参量振荡器谐振阈值的影响.光学参量振荡器的抽运源采用输出波长为1 064 nm的声光调Q Nd:YVO_4激光器,在重复频率为2 kHz、周期极化掺镁铌酸锂晶体的温度为30℃的条件下,光学参量振荡器的振荡阈值仅为48 mW.当抽运功率为94 mW时获得了25 mW的信号光输出,其光-光转换效率为26.6%.     

低阈值温度调谐PPMgLN红外光参量振荡

研究了温度调谐下周期极化镁掺杂铌酸锂晶体的红外光参量振荡特性。采用外电场短脉冲极化技术,在大小为7.0mm×50.0mm×1.0mm的Z切高镁掺杂(摩尔分数0.05)铌酸锂上制备出了准相位匹配光学微结构器件,极化周期为30.0μm。以输出波长为1064nm的声光调QNd:YAG固体激光器作为基频泵浦光开展了光参量振荡研究。实验表明:泵浦该PPMgLN晶体,实现了室温下低阈值红外光参量振荡产生,阈值功率仅为45mW(重复频率1kHz)。在泵浦输入功率为225mW时,有36mW信号光输出,转换效率达到16.0%,通过调谐晶体温度(20~180℃),获得了调谐范围为1503~1550nm波段的OPO信号光,实现了低阈值可调谐红外光的稳定输出。     

Ba(NO3)2晶体受激拉曼散射的角度分布和脉冲压缩

报道了利用重复频率为30 Hz,波长为532 nm 的Nd∶YAG倍频激光单次通过抽运硝酸钡（Ba(NO3)2）晶体（晶体由水溶液降温法生长,长度为48 mm,横截面为10 mm×10 mm）,获得高效率的一阶（563 nm）,二阶（599 nm）和三阶（639 nm）斯托克斯光的实验结果.硝酸钡晶体沿着［110］晶轴方向切割.观测到一、二、三阶斯托克斯光呈锥形环分布,一、二、三阶斯托克斯光的散射外边缘与抽运光轴线间的夹角大小分别为1.7°,3.5°,5.0°.同时也观测到Ba(NO3)2的SRS角度分布与抽运光强度无关.定性分析认定,Ba(NO3)2的SRS角度分布主要是由相位匹配过程决定的.测得抽运光、一、二、三阶斯托克斯光的脉宽分别为11.6 ns,9.8 ns,8.4 ns和4.5 ns.当抽运光功率密度约为150 W/cm2时,获得一、二、三阶斯托克斯光的最大光光转换效率,分别为33.5%,8.8%和3.4%. 此外,由于晶体中的热沉积效应,观察到了Ba(NO3)2晶体的SRS转换效率饱和现象.     

低对称性非线性光学晶体硼酸铋(BIBO)的1064nm三倍频性质

采用高温溶液法成功生长出高光学质量的硼酸铋 (BIBO)晶体 ,尺寸达到 2 4mm× 19mm× 35mm ,质量为4 8g。对BIBO晶体进行了定向 ,并测量了该晶体的主轴折射率。讨论了BIBO晶体的 10 6 4nm三倍频性质 ,包括相位匹配角、有效非线性光学系数deff、容限角、走离角等。结果表明 ,BIBO晶体的最佳三倍频方向为 (137.7°,130°) ,其有效非线性光学系数值达到 3.6 0 pm/V ,属I类相位匹配。就主平面内的相位匹配方向而言 ,(14 6 .4°,90°)具有最大的有效非线性光学系数值 ,为 3.16pm/V。在 10 6 4nm的腔外三倍频实验中 ,(14 6 .4° ,90°)BIBO晶体的转换效率达到 39.5 % ,角度容限半宽为 0 .2 2mrad·cm ,该数值与 0 .175mrad·cm的计算值基本符合。由于(33.6°,90°)BIBO晶体的有效非线性光学系数较小 (0 .31pm/V) ,其三倍频转换效率小于 5 %。     

面向PEM应用的γ射线探测器研究

正电子发射乳腺照相术(Positron Emission Mammography, PEM)获得的是乳腺的实时高分辨率动态的功能图像, 从而为在更广范围里研究治疗乳腺癌的方法提供了可能. 大多数的PEM探测器采用紧凑型无机闪烁晶体阵列与光电探测器相耦合的形式, 故光电信号转换器件在PEM探测器中起着非常重要的作用. 探测器基于新型平面面板位置敏感型光电倍增管(Flat Panel Position Sensitive PMT, FP-PS-PMT), 配以锗酸铋(Bi₄Ge₃O₁₂, BGO)晶体阵列. PS-PMT型号为R8400-00-M256型FP-PS-PMT, 有效面积大于90%. 晶体阵列为20×20, 单个晶体尺寸为2mm×2mm×20mm. 实验验证表明该探测器具有良好的空间分辨本领和能量分辨本领, 空间分辨率达到2.0mm半高宽(Full Width Half Maximum, FWHM), 能量分辨率达到23% FWHM.     

窄脉宽LD泵浦全固态绿光激光器的实验研究

研究了绿光平均功率达84W的高稳定声光调Q全固态激光器。通过理论分析和试验研究,针对KTP热效应以及Nd∶YAG棒的热致双折射效应,设计并优化了谐振腔来压窄脉宽。采用35个20W的高功率LD侧面抽运Nd∶YAG棒和Ⅱ类相位匹配KTP晶体(24℃时相位匹配角为Φ=23.6°,θ=90°,尺寸为7mm×7mm×7mm),采用双声光Q开关,高效平凹结构,实现了高功率内腔倍频激光器的稳定运转;在抽运电流25A时,获得了重复频率为10kHz,脉冲宽度优于45ns,输出功率为84W的高功率、高重频、窄脉宽绿光(532nm)输出,光_光转换效率为14.3%,不稳定度为±3%。     

104W内腔倍频全固态Nd∶YAG绿光激光器

报道了一台高功率内腔倍频全固态Nd∶YAG绿光激光器 ,针对KTP晶体热效应和激光热稳定腔 ,采取了对KTP晶体进行低温冷却的优化措施 ,以便减少KTP晶体的热效应导致的相位失配 ,同时兼顾了Nd∶YAG棒的热致双折射效应和KTP晶体热透镜效应 ,设计了热稳定谐振腔 ;实验中采用 80个 2 0W激光二极管阵列侧面抽运Nd∶YAG棒和Ⅱ类相位匹配KTP晶体 (在 2 7℃时相位匹配角为 =2 3.6° ;θ =90° ,尺寸为 7mm× 7mm× 10mm)内腔倍频技术 ,谐振腔腔长为 5 30mm ,KTP晶体的冷却温度为 4 .3℃ ,抽运电流为 18.3A时 ,实现平均功率达 10 4W、脉冲宽度为 130ns的 5 32nm激光输出 ;其重复频率为 2 0 .7kHz。光光转换效率为 10 .2 %。     

双共振准相位匹配光学参量振荡器的调谐特性

利用全固化单频Nd：YVO4激光器泵浦双共振难相位匹配铌酸锂连续光学参量振荡器，实验研究了该光学参量振荡器下转换光的调谐特性。通过改变PPLN晶体的温度及OPO的腔长，下转换光的调谐范围分别为189nm和175nm，通过改变泵浦光频率，信号光频率连续调谐375MHz。实验结果与理论计算值基本吻合。     

Mid-infrared optical parametric oscillator based on ZnGeP2 pumped by 2-μm laser

We present a 3 5 μ m optical parametric oscillator (OPO) based on ZGP pumped by KTP OPO 2.1-μ m laser. The tuning curves of ZGP OPO are calculated. The 8 ×6 ×18 (mm) ZGP crystal, whose end faces are antireflection coated at 2.1 and 3.7 4.6 μ m, is cut as θ =53.5°, φ =0°. When the pump power of 2.1-μ m polarized laser is 15 W at 8 kHz, 5.7-W output power and 46.6% slope efficiency are obtained with a ZGP type I phase match. Central wavelengths of the signal and idler lasers are 4.10 and 4.32 μ m, respectively. Pulse duration is about 27 ns. Beam quality factor M 2 is better than 1.8. The tunability of 3 5 μ m can be achieved by changing the angle of the ZGP crystal.     

Wavelength-agile mid-infrared (5-10 microm) generation using a galvano-controlled KTiOPO4 optical parametric oscillator

A wavelength-agile mid-infrared (IR) ZnGeP2 (ZGP) optical parametric oscillator (OPO) using a galvano-controlled double-crystal KTiOPO4 (KTP) OPO was demonstrated. The mid-IR wavelength was tuned by varying the KTP OPO pump wavelength while the ZGP crystal angle remained fixed. Rapid tuning of the KTP OPO was achieved by changing the crystal angle by using the galvano scanner. Our mid-IR source can jump to a different wavelength without scanning through the intermediate wavelengths while also permitting continuous-wavelength scanning. The mid-IR source can be tuned from approximately 5to10 microm at a phase-matching angle of 51 degrees , while the pump wavelength is controlled in the 1.95-2.2 microm range.     

Pump tuned wide tunable noncritically phase-matched ZnGeP2 narrow line width optical parametric oscillator

A line tunable singly resonant noncritically phase matched narrow band width ZnGeP₂ (ZGP) optical parametric oscillator pumped by the output idler radiation from a KTA OPO based on a 20 mm long KTA crystal pumped from a Q-switched Gaussian shaped Nd:YAG laser beam with a grating having grooves density 85 lines/mm has been demonstrated in the spectral ranges of 3–7 μm. The measured threshold of oscillation energy was 10 μJ. The conversion efficiency was 20.5% and slope efficiency of the ZGP OPO was 20% using a 23 mm long ZGP crystal at 26 mm cavity length. Line width of the generated infrared radiation from ZGP OPO was 37–60 nm.     

Performance evaluation of ZnGeP2 optical parametric oscillator pumped by a Q-switched Tm,Ho:GdVO4 laser

A doubly resonant ZnGeP2 （ZGP） optical parametric oscillator （OPO） pumped by a novel Tm,Ho：GdVO4 laser was demonstrated. Cryogenic Tin（5 at.-%）, Ho（0.5 at.-%）：GdVO4 laser with high pulse repetition frequency （PRF） of 10 kHz at 2.05 μm was employed as pumping source of ZGP OPO. The 15-mm-long ZGP crystal, 55° cut for I-type phase-matching with low absorption coefficient less than 0.05 cm^-1 at 2 μm, was placed in a piano-piano cavity with resonator length of 30 mm. The ZGP OPO generated a total combined output power of 1.2 W at 3.75 and 4.52 μm under pumping power of 5.3 W, corresponding to slope efficiency of 40% from incident 2μm laser power to midinfrared （Mid-IR） output. A widely tunable range from 3.0 to 6.5 μm was achieved by changing the crystal angle only 3.5°.     

Comparative investigation of long-wave infrared generation based on ZnGeP2 and CdSe optical parametric oscillators

Long-wave infrared (IR) generation based on type-II (o→e+o) phase matching ZnGeP₂ (ZGP) and CdSe optical parametric oscillators (OPOs) pumped by a 2.05 μm Tm,Ho:GdVO₄ laser is reported. The comparisons of the birefringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally. For the ZGP OPO, up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency (PRF) with a slope efficiency of 7.6%. This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm. For the CdSe OPO, we demonstrate a 64 mW output at 8.9 μm with a single crystal 28 mm in length.     

Comparative investigation of long-wave infrared generation based on ZnGeP2 and CdSe optical parametric oscillators

Long-wave infrared(IR) generation based on type-II(o→e+o) phase matching ZnGeP 2(ZGP) and CdSe optical parametric oscillators(OPOs) pumped by a 2.05 μm Tm,Ho:GdVO 4 laser is reported.The comparisons of the birefringent walk-off effect and the oscillation threshold between ZGP and CdSe OPOs are performed theoretically and experimentally.For the ZGP OPO,up to 419 mW output at 8.04 μm is obtained at the 8 kHz pump pulse repetition frequency(PRF) with a slope efficiency of 7.6%.This ZGP OPO can be continuously tuned from 7.8 to 8.5 μm.For the CdSe OPO,we demonstrate a 64 mW output at 8.9 μm with a single crystal 28 mm in length.     

Broadly tunable noncritically phase-matched ZnGeP2 optical parametric oscillator with a 2-microJ pump threshold

We report a high-repetition-rate (1-10-kHz) optical parametric oscillator (OPO) based on noncritically phase-matched ZnGeP2 (ZGP). The pump source was an OPO based on periodically pole lithium niobate that was pumped in turn by a Q-switched diode-pumped 1-microm Nd:YAG laser. The ZGP OPO yielded continuously tunable output from 3.7 to 10.2 microm by tuning of the pump wavelength from 2.3 to 3.7 microm. At the optimal pump focusing, the minimum ZGP OPO threshold achieved was 2 microJ, which is to our knowledge the lowest ever reported for a singly resonant OPO. The output energy in the 6-8-microm range was > 20 microJ, and the quantum efficiency of converting 1-microm radiation to the mid IR exceeded 10%.     

A High-Power,Long-Wavelength Infrared ZnGeP<Subscript>2</Subscript> Opo Pumped by a <Emphasis Type="Italic">Q</Emphasis>-Switched Tm,Ho:GdVO<Subscript>4</Subscript> Laser

We report a high-power, long-wavelength infrared ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a Q-switched Tm,Ho:GdVO₄ laser. The wavelength tuning range of 7.8–9.9 μm is realized by rotating the external angle of the ZGP crystal. We obtain an output power over 30 mW across the whole wavelength range and achieve a 1.71 W output power at 8.08 μm by transmitting the OPO parameters, corresponding to an idler laser slope efficiency of 12.1%.     

A ring ZnGeP2 optical parametric oscillator pumped by a Ho:LuAG laser

We have demonstrated that we believe to be the first ring ZnGeP₂ (ZGP) optical parametric oscillator (OPO) pumped by a pulsed Ho:LuAG laser. The maximum output power of the ring ZGP OPO laser was 5.51 W at 13.1 W incident Ho pump power, corresponding to a slope efficiency of 59.0 %. The ZGP OPO laser produced 14 ns mid-infrared pulses in the 3.72–4.01 and 4.37–4.75 μm spectral regions simultaneously. In addition, the continuous wave Ho:LuAG laser generated 26.5 W of linearly output at 2,094.4 nm at the absorbed Tm pump power of 49.9 W.     

Electro-optic spectral tuning in a continuous-wave, asymmetric-duty-cycle, periodically poled LiNbO(3) optical parametric oscillator

We demonstrate electro-optic spectral tuning in a continuous-wave periodically poled LiNbO(3) (PPLN) optical parametric oscillator (OPO). We achieve 8.91 cm(-1) of rapid spectral tuning, with a linear tuning rate of 2.89 cm(-1) /(kV/mm), by applying electric fields up to +/-1.5 kV/mm across the crystal while it is operating within the OPO. Intentionally poling the PPLN crystal with an asymmetric domain structure enables tuning, and numerical predictions closely match the experimental observations. The tuning is considerably larger than the typical operational bandwidth of the OPO, indicating that we are in fact shifting the gain curve of the PPLN crystal.