Compact, 220-ps visible laser employing single-pass, cascaded frequency conversion in monolithic periodically poled lithium niobate

We report the first demonstration to our knowledge of 220-ps visible laser generation from passively Q-switched-laser pumped periodically poled lithium niobate (PPLN) in a single-pass, cascaded frequency-conversion process. The monolithic PPLN consists of a 1-cm section for frequency doubling the 1064-nm Nd:YAG pump laser to a 532-nm laser and a subsequent 4-cm section for generating the visible laser in a 532-nm-pumped optical parametric generation (OPG) process. In generating the 622.3-nm OPG signal wavelength we measured a 3.0-microJ/pulse pump threshold at the 1064-nm wavelength, 16% overall efficiency, and 35% slope efficiency at two times threshold. At 10(-6) pump duty cycle and 20-mW average power in the visible, photorefractive damage was not observed at the phase-matching temperature of 40.3 degrees C.     

基于单块周期极化铌酸锂晶体级联三倍频的440 nm蓝光固体激光器

阐述了一种基于单块周期极化铌酸锂晶体级联三倍频实现440 nm蓝光输出的实验方案。根据周期极化铌酸锂晶体的Sellmeier方程以及倍频与和频的相位匹配条件,在一块周期极化铌酸锂晶体上设计了两段不同的极化周期,使其在同一工作温度下能分别实现倍频与和频,在先后经过倍频与和频后,实现级联三倍频输出。实验采用Nd: YAG产生的1319 nm光作为基频光,重频400 Hz,脉宽110 ns,横向和纵向光束质量因子分别为1.81和2.65。耦合进周期极化铌酸锂晶体后,出射光中检测到660 nm的红光和440 nm的蓝光。通过调整工作温度和入射基频光功率,得到2.4 mW的最大蓝光输出,此时工作温度55.5 ℃,基频光功率530 mW。实验结果验证了单块晶体实现级联三倍频440 nm蓝光输出的可行性。     

A compact and high efficiency diode pumped green laser based on MgO doped PPLN

In this work, an efficient intra-cavity second harmonic generation of green laser in a periodically poled MgO doped LiNbO₃ (MgO:PPLN) bulk crystal using a compact Nd:YVO₄ laser as a fundamental laser source is reported. Different length, different working temperature MgO:PPLN crystals are tested and investigated in the SHG experiments. The maximum output power at 532 nm is 6.2 W at the absorbed pump power at 808 nm of 14 W, the optical to optical conversion efficiencies from 808 to 532 nm and 1064 to 532 nm are 43 and 77%, respectively, the instability in 2 hours is less than 5%.     

Widely and continuously tunable optical parametric generator infrared laser

The experimental results of a high efficiency infrared laser are demonstrated on a quasi phase matched optical parametric generator in PPMgLN (5% MgO doping) pumped by a 1064 nm Nd:YAG laser. A broad continuous signal spectrum 1.56?C1.67 ??m are obtained by tuning the crystal temperature from 20°C to 200°C. When the average pump power is 1.82 W with about 70 ns pulse duration operating at a repetition rate of 10 kHz, the maximum total output power of the PPMgLN OPG is about 323.58 mW consisting of 210 mW of 1.639 ??m signal radiation and 113.58 mW of 3.02 ??m idler radiation.     

Widely tunable PPLN/IOPO driven by a diode-end-pumped Q-switched Nd:YVO<Subscript>4</Subscript> laser

This paper reported a broadband tuning intracavity optical parametric oscillator (IOPO), based on the multiple grating periodical poled lithium niobate (PPLN) pumped by a acoustic-optical (AO) Q-switched Nd:YVO₄ laser. The widely tunable OPO output signal wavelength range from 1390 to 1605 nm, which was obtained by changing PPLN poling period from 27.8 to 31.6 μm at a certain temperature of 46°C, while the continuous tuning range was measured from 1475 to 1592 nm with the PPLN poling period of 30 μm by varying the temperature of nonlinear crystal PPLN from 50 to 120°C. The maximum output power of 0.92 W at 1534 nm with the minimum pulse width of 5.17 ns was generated under the incident pump power of 9.6 W at 808 nm. The corresponding peak power and single pulse energy were calculated to be 5.94 kW and 30.7 μJ, respectively. The M ₂-factor was measured to be 2.01 at the signal power of 0.4 W.     

Tunable,continuous-wave single-resonant optical parametric oscillator with output coupling for resonant wave

We present a continuous-wave singly-resonant optical parametric oscillator with 1.5% output coupling of the resonant signal wave, based on an angle-polished Mg O-doped periodically poled lithium niobate(Mg O:PPLN), pumped by a commercial Nd:YVO4laser at 1064 nm. The output-coupled optical parametric oscillator delivers a maximum total output power of 4.19 W with 42.8% extraction efficiency, across a tuning range of 1717 nm in the near- and mid-infrared region.This indicates improvements of 1.87 W in output power, 19.1% in extraction efficiency and 213 nm in tuning range extension in comparison with the optical parametric oscillator with no output coupling, while at the expense of increasing the oscillation threshold by a factor of ～ 2. Moreover, it is confirmed that the finite output coupling also contributes to the reduction of the thermal effects in crystal.     

窄线宽1064 nm光纤激光泵浦高效率中红外3.8μm MgO:PPLN光参量振荡器

采用放大1064 nm掺镱光纤激光器作为泵浦源,实现了中红外3.8μm MgO:PPLN光参量振荡(OPO)激光输出。在泵浦源中,采用分布式反馈激光器(DFB)作为种子源来实现光纤激光窄线宽的调制,实现线宽2.5 nm到0.1 nm的压缩,最大平均输出功率可达40 W。进一步对不同泵浦线宽条件下中红外3.8μm MgO:PPLN OPO激光进行研究,最终在泵浦功率为18.1 W、线宽为0.1 nm、重频为1 MHz、脉宽为2 ns时,获得了最高平均输出功率为2.06 W的3822.5 nm激光输出,光-光转换效率为11.38%,光束质量为M2=2.34,提高了窄线宽泵浦对中红外MgO:PPLN OPO激光输出效率。     

1653 nm光参量放大器及在甲烷遥测方面的应用

基于掺氧化镁的周期性极化铌酸锂（MgO:PPLN）晶体,研究了连续波种子光注入结构的光参量放大器(OPA)。采用重复频率为10 kHz、最大平均输出功率为6 W的1064 nm高频脉冲激光作为抽运源,晶体的极化周期为31.02 m,在119 ℃工作温度下,将连续分布式反馈激光器（DFB）作为种子注入,在1652.3 nm处得到最大平均功率为125 mW的OPA信号光输出,量子转换效率为7.47％。实验通过改变注入种子光波长,实现了信号光nm级范围的调谐输出。信号光通过10 m外甲烷气池,观察到其光谱强度明显下降,初步验证了信号光在甲烷遥测领域的可行性。与用种子光直接检测相比,信号光强度更高,检测距离及灵敏度均有较大优势。     

2.5-W, continuous-wave, 629-nm solid-state laser source

We report an efficient, high-power, cw, 629-nm laser source based on a diode-pumped Nd:YAG laser and a periodically poled lithium niobate (PPLN) frequency converter. This device integrates two separate frequency-conversion steps in a single crystal, taking advantage of the ability to fabricate PPLN with nearly arbitrary grating periods and phase-matching temperatures. This device uses a single PPLN crystal that has two grating regions in series. The first region quasi-phase matches a standard optical parametric oscillator process (1064nm?1540nm +3450nm), and the second region quasi-phase matches a sum-frequency process whereby the pump and the signal light make red light (1064nm+1540nm ?629nm). Using a four-mirror ring cavity, we were able to convert 21% of the 1064-nm pump to 629-nm output, yielding 2.5W of red output with 11.8W of input.     

半导体激光直接倍频的488nm蓝光激光器

利用波导型准相位匹配周期极化反转铌酸锂(PPLN)晶体直接倍频波长为976 nm的连续半导体激光二极管,在最佳晶体工作温度(28℃)下,获得了波长为488 nm的连续蓝光输出,最大输出功率大于20 mW。所用的晶体尺寸为8 mm×1.4 mm×1 mm,波导截面为4.5μm×3.5μm,极化周期为5.2μm。研究了波导型周期极化反转铌酸锂晶体的倍频效率与温度的关系,与普通的周期极化反转铌酸锂相比,倍频效率与温度关系的敏感度较低。同时,由于晶体可以在室温下工作,简化了加温与温控部件,提高了整机的工作效率。在此实验的基础上,制成了一台小型的全固态488 nm连续蓝光激光器。     

Continuous-tunable 4.144-4.851 μm twin-MgO:PPLN cascaded optical parametric generator pumped by a 1.342 μm Nd:GdVO4 laser

An all-solid-state mid-infrared optical parametric generator with wide tunability by using multi-grating periodically poled 5 mol.-% MgO-doped lithium niobate (MgO:PPLN) is reported. The pump source is a diode-pumped Q-switched Nd:GdVO₄ laser operated at 1.342 μm with pulse width of 150 ns and repetition rate of 50 kHz. To extend the interaction length, two identical multi-grating MgO:PPLN crystals have been cascaded in the OPG system. When the incident pump average power is 10 W, the obtained maximum idler output power is 340 mW at 4.144 μm. Compared with only using one multi-grating MgO:PPLN crystal, the obtained idler output power increases by 20.1%. 4.144-4.851 μm continuous-tunable idler output is obtained with six grating periods from 29 to 31.5 μm and temperature from 40 to 200 °C. To our knowledge, this is the first time to use 1.342 μm laser as the pump source of OPG.     

波长可调谐的瓦级连续橙红光激光器

介绍了基于复合腔结构的全固态波长可调谐的连续橙红色激光的输出特性。该复合腔由一个使用周期极化晶体MgO:PPLN的信号光单谐振光参量振荡器和一个LD侧面泵浦Nd:GdVO₄晶体的1 062.9 nm基频光谐振腔构成。s-偏振1 062.9 nm泵浦光抽运单谐振光参量振荡器产生s-偏振信号光腔内独立振荡。通过复合腔结构的优化设计,使独立振荡的p-偏振1 062.9 nm基频光与s-偏振信号光在2个子腔的重叠区内通过Ⅱ类角度匹配KTP晶体的腔内和频过程获得橙红色激光。当MgO:PPLN晶体的调谐温度从30 ℃上升至200 ℃时,s-偏振信号光的中心波长产生红移,导致其与p-偏振1 062.9 nm基频光和频产生的橙红色激光的中心波长从620.2 nm红移至628.9 nm。同时测得中红外波段闲频光的中心波长从3 714.2 nm蓝移至3 438.3 nm。在30 ℃最低设定温度时, 中心波长620.2 nm的橙红色激光和中心波长3 714.2 nm的闲频光最大连续输出功率分别达到2.0 W和2.9 W。     

Actively Q-switched Nd:YVO4 laser using an electro-optic periodically poled lithium niobate crystal as a laser Q-switch

We demonstrate a low-voltage and fast laser Q-switching by using an electro-optic periodically poled lithium niobate (EO PPLN) crystal. The half-wave voltage measured from the EO PPLN crystal was 0.36 V x d (microm)/L (cm), where d is the electrode separation and L is the electrode length. When a 13-mm-long EO PPLN was used as a laser Q switch at 7-kHz switching rate, we measured an approximately 12-ns pulse width and approximately 0.74-kW laser pulses at 1064-nm wavelength from a diode-pumped Nd:YVO4 laser with continuous 1.2-W pump power at 809-nm wavelength.     

A 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator with cw diode laser injection seeding

We report on an injection-seeded 9.5-W 82-MHz-repetition-rate picosecond optical parametric generator (OPG) based on a 55 mm long crystal of periodically poled lithium niobate (PPLN) with a quasi-phase-matching (QPM) grating period of 29.75 μm. The OPG is excited by a continuously diode pumped mode-locked picosecond Nd:YVO₄ oscillator-amplifier system. The laser system generates 7 ps pulses with a repetition rate of 82.3 MHz and an average power of 24 W. Without injection-seeding the total average output power of the OPG is 8.9 W, which corresponds to an internal conversion efficiency of 50%. The wavelengths of the signal and idler waves were tuned in the range 1.57–1.64 μm and 3.03–3.3 μm, respectively, by changing the crystal temperature from 150 °C to 250 °C. Injection seeding of the OPG at 1.58 μm with 4 mW of single frequency continuous-wave radiation of a distributed-feedback (DFB) diode laser increases the OPG output to 9.5 W (53% conversion efficiency). The injection seeding increases the pulse duration and reduces the spectral bandwidth. When pumped by 10 W of 1.06 μm laser radiation, the duration of the signal pulses increased from 3.6 ps to 5.5 ps while the spectral bandwidth is reduced from 4.5 nm to 0.85 nm. Seeding thus improved the time-bandwidth product from 1.98 to a value of 0.56, much closer to the Fourier limit. Received: 29 April 2002 / Published online: 8 August 2002     

Widely tunable narrow-linewidth nanosecond optical parametric generator with self-injection seeding

This paper reports a widely tunable narrow-linewidth nanosecond optical parametric generator (OPG) with a pulse-repetition rate of 10 kHz. The OPG consists of a 55-mm-long periodically poled lithium niobate crystal with a domain period of 29.5 m. At an average pump power of 2.0 W the OPG emitted 0.33 W of signal power and 0.17 W of idler power. The wavelength and spectral width of the OPG are controlled by self-injection seeding. For this purpose, a small fraction of the OPGs pulsed signal radiation is used as seed radiation for the next OPG pulse. In order to overlap in time the seed pulse with the succeeding pump pulse, the seed pulse is delayed by a 22-km-long single-mode fiber. For narrowing the spectrum of the seeded OPG output, the seed radiation is spectrally filtered by a tunable fiber Fabry–Perot interferometer (FFPI). The OPG signal radiation could be tuned from 1547 to 1605 nm by changing the OPGs crystal temperature and by tuning simultaneously the FFPI. The corresponding idler wave tuned from 3157 to 3413 nm. Within the whole tuning range, the linewidth of the signal wave was less than 185 MHz. Compared to the 240-GHz linewidth of the free-running OPG, the linewidth of the seeded OPG is thus narrowed by more than three orders of magnitude. By tuning the FFPI, continuous wavelength tuning has been demonstrated within the gain spectrum of the OPG over a range of 820 GHz. PACS 42.65.Yj; 42.79.Nv; 42.79.Qx     

Period and temperature tuning of cascaded opticalparametric oscillator based on periodically poled LiNbO3

We report the broadly tunable source by a cascaded optical parametric oscillator in the periodically poled LiNbO_3 (PPLN) with domain grating period and temperature tuning. The optical parametric oscillator was pumped by a passive Q-switched Nd:YVO_4 laser. Multi-wavelength outputs from visible to infrared were obtained. The temperature of the PPLN crystal changed within the range of 70－150℃ with different periods of PPLN. The tunable range covered from 433 to 1657nm.     

A compact,widely tunable intracavity PPLN optical parameter oscillator driven by an Nd:YAG/Cr:YAG composite crystal laser

Based on periodically poled lithium niobate (PPLN), a mini intracavity optical parameter oscillator (IOPO) driven by an diode-end-pumped composite Nd³⁺:YAG/Cr⁴⁺:YAG laser was demonstrated. The PPLN wafer has 20 domain reversal periods from 27.8 to 31.6 μm with a step of 0.2 μm between the neighbor periods. The output signal laser of OPO can be widely tunable in the range of 1402–1676 nm by changing the period at a certain temperature of 50°C. Under the diode pump power of 14 W, the maximum average output power of 600 mW at 1534 nm with pulse width of 2.0 ns and repetition rate of 16 kHz was obtained, corresponding to a peak power of 18.7 kW and a single pulse energy of 37.5 μJ, respectively.     

Online monitoring of ethane traces in exhaled breath with a difference frequency generation spectrometer

We report a transportable mid-infrared laser cavity leak-out spectrometer for online detection of trace gases. The laser spectrometer is based on continuous-wave difference-frequency generation in the wavelength region around 3 μm. Sensitive spectroscopic trace gas monitoring was achieved using a high-finesse ring-down cavity. For difference-frequency generation, we use a periodically poled lithium niobate (PPLN) crystal, pumped by a Nd:YAG laser (signal wave) and a diode laser (pump wave) with a tapered amplifier. A maximum power of 280 μW near λ=3.3 μm is achieved using a pump power of 180 mW at 807 nm, a signal power of 890 mW at 1064.46 nm, and a 50-mm-long PPLN crystal. The resulting system proved to be a unique tool with high sensitivity and specificity for rapid and precise breath testing. We demonstrate spectroscopic online monitoring of ethane traces in exhaled human breath with a precision of 270 parts per trillion (1σ) and a time resolution of 1 s. PACS 42.62.Be; 42.60.-v; 07.57.Ty     

Electro-optic periodically poled lithium niobate Bragg modulator as a laser Q-switch

We report an electro-optic Bragg modulator using a periodically poled lithium niobate (PPLN) crystal. We measured a half-wave voltage of 160 V when transmitting a 1064 nm laser through a 14.2 mm long, 780 microm thick, 20.13 microm period PPLN crystal at the Bragg angle. We also demonstrated a Q-switched Nd:YVO(4) laser using such a PPLN Bragg modulator as its Q-switch, producing 7.8 ns, 201 microJ pulses at a 10 kHz repetition rate when pumped by a 19.35 W diode laser at 808 nm.     

Generation of ultrafast mid-infrared laser by DFG between two actively synchronized picosecond lasers in a MgO:PPLN crystal

We report the difference-frequency generation (DFG) of ultrafast mid-infrared laser radiation around 3???m between two picosecond laser pulses with the center wavelengths of 800?nm and 1064?nm in a MgO:PPLN crystal at room temperature. The two laser pulses were generated from the actively synchronized picoseconds Ti:sapphire and Nd:YVO₄ oscillators. We measured the DFG wavelengths tunable from 3.19?C3.29???m and the output power is potential to be several mW. This experiment proves a possible roadmap for ultrafast mid- and far-infrared laser radiation generation and even for the THz radiation.