A 7.5?W quasi-continuous-wave sodium D2 laser generated from?single-pass sum-frequency generation in LBO crystal

We report a high-power, narrow linewidth and tunable quasi-continuous-wave (QCW) yellow laser system at 589.159?nm. The system is of a design employing single-pass sum-frequency generation (SFG) in a LBO crystal by mixing the 1064?nm with 1319?nm lines from a two diode-side-pumped Nd:YAG master oscillator-power amplifier (MOPA) laser system. With the pump power of 35?W at 1064?nm and 25?W at 1319?nm, a 7.5?W QCW output of the SFG yellow laser at 589.159?nm, which is the vacuum wavelength of a general sodium D₂ line, is obtained with a linewidth less than 0.7?GHz and a beam-quality factor M ²=1.2. The wavelength of the laser can be precisely step-tuned from 589.148 to 589.167?nm with an increment of 0.13?pm by means of a temperature-controlled etalon.     

High-power, continuous-wave, mid-infrared optical parametric oscillator based on MgO:sPPLT

We report a stable, high-power, cw, mid-IR optical parametric oscillator using MgO-doped stoichiometric periodically poled LiTaO? (MgO:sPPLT) pumped by a Yb fiber laser at 1064 nm. The singly resonant oscillator (SRO), based on a 30 mm long crystal, is tunable over 430 nm from 3032 to 3462 nm and can generate as much as 5.5 W of mid-IR output power, with >4 W of over 60% of the tuning range and under reduced thermal effects, enabling room temperature operation. Idler power scaling measurements at ~3.3 μm are compared with an MgO-doped periodically poled LiNbO? cw SRO, confirming that MgO:sPPLT is an attractive material for multiwatt mid-IR generation. The idler output at 3299 nm exhibits a peak-to-peak power stability better than 12.8% over 5 h and frequency stability of ~1 GHz, while operating close to room temperature, and has a linewidth of ~0.2 nm, limited by the resolution of the wavemeter. The corresponding signal linewidth at 1570 nm is ~21 MHz.     

Widely tunable narrowband soliton source generation in tellurite microstructured fibers

We demonstrate widely tunable soliton and dispersive wave source generation in a highly nonlinear tellurite microstructured fiber pumped by a 1550 nm femtosecond fiber laser. The spectral range covered by the soliton and dispersive wave source is as wide as 1100 nm from 1150 to 2250 nm. It is shown that the spectral linewidth of the soliton and dispersive wave can be controlled by changing the length of the tellurite microstructured fiber easily owing to the dispersion-induced pulse broadening effects. This light source using tellurite microstructured fiber could open wide applications.     

Ultrabroadband tunable continuous-wave difference-frequency generation in periodically poled lithium niobate waveguides

We report, for what is the first time to our knowledge, widely tunable mid-IR light generation over a range of greater than 1000 nm in the 4 microm region by employing a single quasi-phase-matched periodically poled niobate waveguide at room temperature. The waveguide we used was fabricated by annealed proton exchange based on periodically poled lithium niobate. A peak conversion efficiency of 10%/W and a linewidth as small as 37 MHz were achieved. The developed mid-IR light generator may find wide applications in trace gas detection of multiple atmospheric species and high-resolution spectroscopy.     

激光线宽对单次通过PPMgO:LN晶体倍频效率的影响

通过单次穿过PPMgO:LN晶体产生了2.06 W的780 nm可调谐的连续倍频光. 采用1560 nm的分布反馈式(DFB)半导体激光器、光栅外腔半导体激光器(ECDL)和分布反馈式掺铒光纤激光器(DFB-EDFL)分别作为掺铒光纤放大器(EDFA)的注入光源, 所用的EDFA具有保持窄线宽的功能, 因此可以忽略它对基波线宽的展宽. 研究了激光线宽对单次通过PPMgO:LN 晶体的倍频效率的影响. 控制三台激光器各自注入EDFA的功率一致, 同时也保持EDFA 的输出功率. 在基波功率为12.42 W 时, 使用DFB半导体激光器注入EDFA时得到了1.36 W的780 nm倍频光输出, 转换效率为11.0%; 使用ECDL作为种子源时得到了1.78 W 的780 nm倍频光输出, 转换效率为14.3%; 使用DFB-EDFL作为种子源时得到了2.06 W的780 nm倍频光输出, 转换效率为16.6%. 测得三台种子激光器的线宽分别为1.2 MHz (DFB), 200 kHz (ECDL)和600 Hz (DFB-EDFL). 线宽越窄, 倍频效率越高, 实验结果与理论分析一致.     

同带泵浦高功率超荧光光源

报道了一台基于同带泵浦技术的主振荡功率放大(MOPA)结构超荧光光纤光源。首先利用自行搭建的超荧光种子源获得了半高全宽(FWHM)线宽10.3 nm的宽谱超荧光种子,经光谱滤波得到FWHM线宽1.8 nm的窄谱种子光;种子光经二级预放大器放大至104.4 W后注入主放大器;主放大器最高输出功率3.14 kW,最高输出功率时光光转换效率80.74%,光谱FWHM线宽4.68 nm,光束质量因子为1.59。进一步提高系统泵浦功率有望获得更高功率输出。     

双纵模窄线宽光纤拉曼放大器

 报道了一台实现了双纵模窄线宽激光输出的光纤拉曼放大器。利用中心波长1 079.7 nm的双纵模窄线宽种子激光器获得了频率间隔1.4 GHz、功率比约3∶1的双纵模输出,各纵模的线宽约为10 MHz;再利用1 031 nm泵浦光对双纵模种子光进行拉曼放大,实现了1.07 W双纵模激光输出。拉曼放大过程中,两个纵模的线宽、频率间隔及功率比保持得很好。     

243 nm稳频窄线宽半导体激光器

243 nm是氢原子1S-2S能级跃迁光谱波长. 本文利用Pound-Drever-Hall稳频技术将972 nm光栅反馈外腔半导体激光稳定在一个高精细度低膨胀系数的超稳法布里-珀罗腔上, 通过锥形放大器放大和腔内两次共振增强倍频得到243 nm激光, 最终实现用于探测氢原子1S-2S双光子跃迁的243 nm窄线宽激光.     

利用冲击波作用光子晶体产生蓝光的研究

研究了一种利用冲击波作用光子晶体产生蓝光的新方法.通过模拟光子晶体受冲击波作用后折射率的变化,对470 nm蓝光,设定光子晶体的参量,研究了冲击波引起光子晶体带隙的变化,计算了需要冲击波的速度,分析了影响蓝光线宽和中心波长的因素.结果表明,变频后的光波线宽随冲击波和固定反射面的距离而变化,距离大时,线宽较小,距离小时,线宽较大,可以利用光子晶体的滤波作用对输出光波线宽进行控制,获得带宽稳定的或变化的输出光波.环境温度变化、光子晶体材料吸收特性影响光子晶体的带隙分布,进而影响蓝光的中心波长.研究结果对研制新的蓝光光源具有重要参考价值,同时也为其他相干光源的产生提供了一种新的技术.     

皮秒级BBO晶体光参量发生放大器中线宽的分析与计算

采用全量子理论，建立了皮秒级光参量发生放大器中自发参量辐射产生参量光线宽的数学方程，并对影响参量光线宽的各种物理机制进行计算机模拟、分析和比较。其结果是：在远离简并点时，所产生的参量光线宽很小，而在简并点附近，参量光线宽急剧增大；且泵浦光的发散角和在偏轴方向的泵浦光对参量光线宽的影响较大。这些结果对压缩光参量激光器的线宽具有重要的意义。     

基于平行偏振光注入的1550nm波段垂直腔表面发射激光器获取窄线宽光子微波的理论和实验研究

提出一种基于1550 nm垂直腔表面发射激光器(1550 nm-VCSEL)获取高质量微波信号的全光方案.在该方案中,采用波长位于VCSEL中被抑制模式的中心波长附近、振动方向与VCSEL中主导模式相同的偏振光注入(即平行注入)1550 nm-VCSEL获取高频微波,并借助双光反馈对该高频微波的线宽进行窄化.一方面,基于VCSEL的自旋反转模型,从理论上分析了采用该方案产生微波信号的可行性;另一方面,通过构建相应的实验系统,对该方案产生的微波的特性进行初步实验研究.实验结果表明:在合适的注入条件下,1550 nm-VCSEL能够产生30 GHz左右的微波信号,但该信号的线宽较宽(百兆水平);引入双光反馈后,微波线宽可被压窄两个数量级以上,得到了线宽低于1 MHz、信噪比大于40 d B的微波信号.     

Optimization of 780?nm DFB diode lasers for high-power narrow linewidth emission

We demonstrate the realization of narrow linewidth, high-power ridge waveguide DFB diode lasers emitting near 780?nm. The effects of the coupling coefficient, the laser chip length, and the fabrication process onto the spectral linewidth are discussed. By optimizing both the cavity length and the coupling coefficient, we achieve an intrinsic spectral linewidth as small as 35?kHz at an output power of 270?mW.     

95 GHz millimeter wave signal generation using an arrayed waveguide grating dual wavelength semiconductor laser

We report the generation of a 95?GHz carrier frequency by optical heterodyning of two wavelengths from adjacent channels from an arrayed waveguide grating-based multiwavelength laser. The extended cavity structure of the device provides low phase noise and narrow optical linewidth, further enhanced by the intracavity filter effect of the arrayed waveguide grating. We demonstrate that the generated RF beat note, at 95?GHz, has a -3 dB linewidth of 250?kHz. To the best of our knowledge, this is the narrowest RF linewidth generated from a free-running dual-wavelength semiconductor laser. The device is realized as a photonic integrated circuit using active-passive integration technology, and fabricated on a multiproject wafer run, constituting a novel approach for a compact, low-cost dual-wavelength heterodyne source.     

有效压缩增益开关DFB激光器光谱线宽的注入时间窗口

实验与理论研究了外光注入种子脉冲有效压缩增益开关DFB激光器光谱线宽的注入时间窗口.发现只有在增益开关光脉冲建立之前约100 ps的时间窗口内，注入种子脉冲方可以有效压缩增益开关DFB半导体激光器光谱线宽, 并且线宽随着注入光强度的增加而减小，可产生低啁啾的近变换极限的超短光脉冲.实验证实，在此时间窗口内注入种子脉冲，增益开关DFB激光器的光谱线宽从0.46 nm压缩至0.08 nm，时间带宽积从2.46降低至0.70.同时理论研究了增益开关DFB半导体激光器的光谱线宽压缩与种子脉冲的注入时间及强度的关系.     

近距离激光外差探测光学极限位移分辨率

通过统计理论和维纳-辛钦定理推导出激光外差探测系统光电流的功率谱函数,分析了光电流谱线分布与激光光源线宽、中频信号频率以及信号光相对本振光传输延迟时间的关系,修正了相关文献中光电流功率谱的理论公式.根据信号与噪声理论建立了激光线宽引起的相位噪声的一维概率分布模型,并据此得到了基于激光波长、探测距离以及激光线宽的极限位移分辨率的数学模型.对光电流的功率谱和外差光学极限位移分辨率进行了相关的数值仿真,结果表明延迟时间与相干时间的关系决定光电流谱线分布的情况.当激光波长为532 nm,激光线宽在1 kHz,探测距离为100 m时,光学极限位移分辨率为0.266 nm,相关文献中的实验数据与理论推导结果相符合.     

Ultraviolet quasi-phase-matched second harmonic generation in surface periodically poled lithium niobate optical waveguides

The compatibility of low concentration (α-phase) proton exchange channel waveguides with electric field surface periodic poling of congruent lithium niobate (SPPLN) crystals has been experimentally demonstrated. With such waveguides, we obtained ultraviolet second harmonic generation (SHG) by first order quasi-phase-matching (QPM), a result made possible by the fabrication, on Z-cut LN crystals, of periodic structures with a pitch down to 750 nm. Nonlinear copropagating QPM-SHG measurements have been carried out on such structures. The pump source was a Ti:sapphire laser with a tunability range of 700–980 nm and a 40 GHz linewidth. We have measured UV continuous wave light at 390 nm by means of a lock-in amplifier and a photodiode with an enhanced response in the UV. The measured conversion efficiency was about 1% W^?1 cm^?2.     

应用于光刻领域中的固态紫外激光源的制作

以半导体侧泵钇铝石榴石激光器为泵浦源,采用腔内泵浦两块三硼酸铯晶体,产生满足高功率与高光束质量要求的三倍频355 nm紫外激光.通过使用法拉第旋转器谐振腔优化设计与热效应补偿提高输出光的光束质量,并且使用体光栅作为输出镜,在实现线宽窄化同时保持准相位匹配的高效性能.该光刻用紫外激光源成功地替代准分子激光器,使用在一套大面积亚纳米级投影式光刻系统上,工作时紫外光输出功率为4.37 W,光束质量因子为2.27.     

Wideband tunable laser phase noise reduction using single sideband modulation in an electro-optical feed-forward scheme

A wideband laser phase noise reduction scheme is introduced where the optical field of a laser is single sideband modulated with an electrical signal containing the discriminated phase noise of the laser. The proof-of-concept experiments on a commercially available 1549 nm distributed feedback laser show linewidth reduction from 7.5 MHz to 1.8 kHz without using large optical cavity resonators. This feed-forward scheme performs wideband phase noise cancellation independent of the light source and, as such, it is compatible with the original laser source tunability without requiring tunable optical components. By placing the proposed phase noise reduction system after a commercial tunable laser, a tunable coherent light source with kilohertz linewidth over a tuning range of 1530-1570 nm is demonstrated.     

Linewidth of collimated wavelength-converted emission in Rb vapour

We present a study of the spectral linewidth of collimated blue light (CBL) that results from wave mixing of low-power continuous-wave laser radiation at 780 and 776 nm and an internally generated mid-IR field at 5.23 μm in Rb vapour. Using a high-finesse Fabry–Perot interferometer, the spectral width of the CBL is found to be <1.3 MHz for a wide range of experimental conditions. We demonstrate using frequency-modulated laser light that the CBL linewidth is mainly limited by the temporal coherence of the applied laser fields rather than the atom–light interaction itself. The obtained result allows the same 1.3 MHz upper limit to be set for the linewidth of the collimated mid-IR radiation at 5.23 μm, which has not been directly detected.     

Widely tunable fourth harmonic generation of a Ti:sapphire laser based on RBBF crystal

Fourth harmonic generation of a tunable Ti:sapphire laser with a repetition rate of 80?MHz and pulse duration ??150 fs has been realized in a single pass with an RbBe₂BO₃F₂ crystal for the first time. A high average power was obtained which was tunable throughout a wide range from 180 to 232.5?nm. The output power over the whole range exceeded 2?mW, the highest being 43.3?mW at 202.5?nm. Moreover, deep-ultraviolet output with powers above 75?mW was obtained at 193.5 and 200?nm under a stronger focusing condition. This is the first attempt at the generation of tunable deep-ultraviolet light without using a KBBF crystal, which is very difficult to grow due to its strong layering tendency, and our attempt may provide new opportunities for the development of all-solid-state deep-ultraviolet coherent light sources.