400 mW and 16.5% wavelength conversion efficiency at 488 nm using a diode laser and a PPLN crystal in single pass configuration

Continuous wave power of more than 400 mW at 488 nm has been generated by frequency doubling of 2.45 W at 976 nm obtained from a distributed Bragg reflector tapered diode laser. This results in a wavelength conversion efficiency of 16.5% and an electrical-to-optical efficiency of more than 4.5%. We used a 50 mm long periodically poled MgO:LiNbO₃ bulk crystal in single-pass configuration for the second harmonic generation. This is to the author’s knowledge the highest output power and the highest wavelength conversion efficiency at 488 nm generated by a monolithic semiconductor laser device in single pass configuration with a bulk crystal. A deviation from the quadratic dependency of the frequency doubling is explained by the decrease of the beam quality of the fundamental wave.     

A tunable diode-laser spectrometer for the MIR region near 7.2 μm applying difference-frequency generation in AgGaSe2

2 and two diode lasers as pump sources are presented. A single-mode Fabry–Pérot-type tunable diode laser (TDL) and an external-cavity diode laser (ECL) were combined to generate radiation in the mid-infrared region near 7.2 μm. With a TDL at a wavelength of approximately 1290 nm and an ECL emitting between 1504 and 1589 nm it was possible to carry out spectroscopic experiments concerning SO₂ at five different phasematching points between 1350 and 1400 cm^-1 by fixing the wavelength of one pump laser and tuning the wavelength of the other. With an input power of 8 mW for the single-mode Fabry–Pérot-type diode laser and 6 mW for the external-cavity laser an output power of about 10 nW was generated. Using the tuning capabilities of the external-cavity laser a spectral region up to 5 cm^-1 could be covered within one scan. Measurements of SO₂ absorption lines at low pressure demonstrate the high-resolution features of the spectrometer. Moreover, these data provide new direct experimental phasematching data for the rarely investigated spectral region at 7.2 μm. Received: 27 October 1997/Revised version: 8 May 1998     

Broad-area diode-laser system for a rubidium Bose-Einstein condensation experiment

We report on master-oscillator power amplification using a broad-area laser diode (BAL) emitting at a wavelength of λ =780 nm. The master oscillator is an injection-locked single-mode diode laser delivering a seeding beam of 35 mW, which is amplified in double pass through the BAL up to 410 mW. After beam shaping and spatial filtering by a single-mode fibre we obtain a clean Gaussian beam with a maximum power of 160 mW. There is no detectable contribution of the BAL eigenmodes in the spectrum of the output light. This laser system is employed for operation of a ⁸⁷Rb magneto-optical trap (MOT) and for near-resonant absorption imaging in a Bose-Einstein condensation experiment. Received: 10 April 2000 / Revised version: 13 June 2000 / Published online: 2 August 2000     

Diode laser spectrometer for high-resolution spectroscopy in the visible range

A high-resolution diode laser spectrometer operating at 657 nm is described. To achieve a narrow linewidth and a high power, a master-slave laser system is employed. The master laser is an extended cavity diode laser whose linewidth is reduced to less than 100 Hz by the FM sideband technique. The slave laser is an AR-coated diode laser and characteristics of injection locking are experimentally studied. The injection current of the slave laser is utilized to stabilize the output power or to produce pulsed output. Using this spectrometer, we probed the intercombination line of Ca and observed high-contrast optical Ramsey fringes with a linewidth of 10 kHz. A velocity-selective Ramsey fringe is also observed in the pulse-mode operation.     

Efficient and high-power intracavity frequency doubled diode-side-pumped Nd:YAG/KTP continuous wave (CW) green laser

Highly efficient continuous wave (CW) green beam generation by intracavity frequency doubling of a diode side-pumped Nd:YAG laser using a single pump head based on a copper-coated flow tube in a V-shaped cavity geometry has been demonstrated. A maximum 30.5 W of CW green power was obtained at a total diode pumping power of 260 W corresponding to 11.7% conversion efficiency of diode pump power to CW green power and 4.7% conversion efficiency of electrical power to CW green power. The performance of the laser by considering the pump power induced thermal lensing effect and the M²-parameter at the fundamental wavelength has been analyzed.     

Noise characteristics of a high-power ytterbium-doped fibre amplifier at 1083 nm

Experimental results are reported for the noise characteristics of an Yb-doped fibre amplifier pumped at 975 nm, used as a booster of a low-noise narrow-linewidth single-frequency 1083-nm wavelength laser diode. The maximum output power of the amplifier is 1.2 W with a gain larger than 30 dB. An increase of the intensity-noise spectral density relative to the signal, by approximately 6.5 dB, is introduced by the amplification process, due to signal-amplified spontaneous-emission (ASE) beat noise. A remarkable increase of the noise level with decreasing frequency is observed below ≈35 kHz, probably due to technical noise of the amplifier pump diodes. The spectral broadening due to amplifier phase noise was measured to be less than 300 Hz with a 5-kHz-linewidth Nd:YAG laser and that for the 300-kHz-linewidth diode laser at 1083 nm is therefore expected to be in the same range. Received: 5 October 1999 / Revised version: 2 December 1999 / Published online: 24 March 2000     

Low Timing Jitter and Tunable Dual-Wavelength Picosecond Pulse Generation from a Fabry--Pérot Laser Diode with External Injection

A novel scheme to generate tunable dual-wavelength optical pulses with low timing jitter at arbitrary repetition rates is proposed and demonstrated experimentally. The pulses are generated from a gain-switched Fabry-Pérot laser diode with two external cw beams for injection seeding simultaneously. The cw light is generated by two independent distributed feedback laser diodes, and their wavelengths can be tuned independently by two temperature controllers. The dual-wavelength pulses with the pulse width of 57 ps, the timing jitter of 340 fs, are obtained. The sidemode-suppression ratio of the output pulses is better than 23dB over a 10-nm wavelength tuning range.     

半导体激光器与光纤光栅对接耦合研究

半导体激光器管芯与光纤光栅的对接耦合对光纤光栅外腔激光器的特性起到关键作用。利用散射矩阵分析了激光器管芯与光纤光栅外腔的对接耦合，发现对接的距离以及对接的耦合效率决定了光纤光栅外腔激光器的性能。在强反馈情况下,激射波长在光纤光栅外腔有效反射率决定的布喇格波长内随对接耦合距离周期性的变化,对弱反馈情况则有些不同。同时对比了两种情况的边模抑制比。该分析为实际制作器件提供了指导。     

All-fiber actively Q-switched Yb-doped laser

An all-fiber actively Q-switched Yb-doped laser is presented. Q-switching is performed by modulating a fiber Bragg grating via a magnetostrictive rod which is fixed to the fiber at the position of the grating. By exposing the rod to a changing magnetic field, the rod is stretched and relaxed causing the Bragg wavelength of the grating to shift and thereby changes the Q-factor of the cavity. Using Yb-doped fiber, pulses at 1052 nm are obtained at repetition rates from 1 to 200 kHz. At 75 kHz, 0.5 μJ pulses with peak powers of 3 W can be produced when 180 mW of pump power is applied. To the knowledge of the authors, this is the first all-fiber actively Q-switched Yb-doped laser presented to date.     

同轴-三平板型水介质脉冲输出开关实验研究

设计了用于脉冲功率装置的4 MV水介质同轴 三平板型输出开关。该脉冲功率装置将由24路相同的独立模块组成，每路模块由Marx发生器、中间储能器、激光触发气体开关、脉冲形成线、水介质脉冲输出开关、脉冲传输线等组成。水介质脉冲输出开关是同轴 三平板结构水介质多通道自击穿开关，由输入输出电极、预脉冲屏蔽板和连接部件组成。进行了有预脉冲屏蔽板结构和无预脉冲屏蔽板结构的自击穿水开关实验研究。有预脉冲屏蔽板结构开关的输入、输出电极都是半球电极，直径分别是8 cm和5 cm；无预脉冲屏蔽板结构开关为针 板结构，输入电极为平板电极，输出电极为直径3 cm的电极棒。Marx发生器充电70 kV，开关的击穿电压为3 MV，放电电流为450 kA。在3 MV等级的击穿电压下，有预脉冲屏蔽板结构开关的抖动约6 ns，没有预脉冲屏蔽板结构开关的抖动减小至3 ns。     

A cw AgGaS2 difference frequency spectrometer with diode lasers as pump sources

2 and two diode lasers as pump sources and experiments with this setup are presented. In contrast to the majority of known applications of the difference frequency mixing with solid state or gas lasers, we apply two single mode diode lasers with emission wavelengths of 690 nm and 805 nm, respectively. By fixing the emission wavelength of one diode laser and tuning the wavelength of the second laser, by changing temperature or excitation current, we can cover typically 0.87 cm^-1 (FWHM) in good agreement with recently published data and theory. With an input power of 20 mW and 6 mW we achieved an output power in the nW-range. To demonstrate the capabilities of the spectrometer we scanned CO and OCS absorption lines near 2107 cm^-1. From these experiments we deduce an overall signal-to-noise ratio of 1000:1 and a spectral resolution better than 30 MHz. With such parameters a trace gas detection of CO at sub-ppm level will be possible. Received: 19 August 1996/Revised version: 5 November 1996     

Parameters of a laser diode with a fiber Bragg grating at different fiber lengths

Theoretical and experimental results are used to demonstrate that an increase in the pump current leads to an increase in the range of continuous variation in the radiation wavelength and power of a laser diode with a fiber Bragg grating with a decrease in the fiber length. An expression for the gain that depends on the carrier density in the laser active area is derived. The watt-ampere and spectral characteristics that are calculated in the two cases are in reasonable agreement.     

Characterization of a high-power tapered semiconductor amplifier system

We have characterized a semiconductor amplifier laser system which provides up to 200 mW output after a single-mode optical fiber at 780 nm wavelength. The system is based on a tapered semiconductor gain element, which amplifies the output of a narrow-linewidth diode laser. Gain and saturation are discussed as a function of operating temperature and injection current. The spectral properties of the amplifier are investigated with a grating spectrometer. Amplified spontaneous emission (ASE) causes a spectral background with a width of 4 nm FWHM. The ASE background was suppressed to below our detection limit by a proper choice of operating current and temperature and by sending the light through a single-mode optical fiber. The final ASE spectral density was less than 0.1 nW/MHz, i.e. less than 0.2% of the optical power. Related to an optical transition linewidth of Γ/2π=6 MHz for rubidium, this gives a background suppression of better than -82 dB. An indication of the beam quality is provided by the fiber coupling efficiency of up to 59%. The application of the amplifier system as a laser source for atom-optical experiments is discussed. Received: 8 May 2000 / Revised version: 21 September 2000 / Published online: 7 February 2001     

Development of narrow-linewidth diode lasers by use of volume holographic transmission gratings

We present two diode laser setups that employ volume holographic transmission gratings to provide optical feedback. The advantage of this kind of grating is high diffraction efficiency and the possibility to place optical elements on both sides of the grating. This allows for advanced external cavities and adjustable feedback efficiency. The first setup is a diode laser in the Littman configuration with the transmission grating replacing the conventional reflection grating. The second setup improves the frequency selectivity by substituting the feedback mirror with a passive resonator. This grating-enhanced external cavity diode laser (GECDL) achieves excellent frequency stability. A prototype of the GECDL setup demonstrates an intrinsic linewidth of 7 kHz and an operation range that covers the full amplification profile of the laser diode.     

End-Pumped Tm:YAG Ceramic Slab Lasers

Lasers from a Tm：YAG slab is end-pumped by continuous-wave output of the Tm：YAG ceramic ceramic am~e reported for the t~rst time to our best knowledge. The Tm：YAG ceramic a laser diode with central wavelength 792nm. At room temperature, the maximum power is 4.5 W, and the sloping efficiency is obtained to be 20.5%. The laser spectrum is centered at 2015nm.     

Second-harmonic generation of 405-nm light using periodically poled KTiOPO4 pumped by external-cavity laser diode with double grating feedback

A frequency-doubled laser diode system for generation of blue–UV light is described. The system is based on an external-cavity high-power laser diode with double feedback from the zeroth and the first orders of a diffraction grating. Light at 405 nm is generated in a single-pass configuration using periodically poled KTiOPO₄. We show that the double grating feedback improves the second harmonic conversion efficiency by several orders of magnitude as compared to the freely running laser. The conversion efficiency may be improved further such that higher second-harmonic powers may be generated.     

基于级联光纤Bragg光栅的外腔半导体激光器三波长同时激射

实现了使用3个级联的光纤Bragg光栅外腔半导体激光器3波长同时激射.3条谱线的峰值波长取决于光纤Bragg光栅的峰值反射波长,分别为1 531.5 nm、1 549.4 nm与1 554.8 nm.注入电流为52 mA时,激光器总输出功率为1 mW.该激光器的主要优点包括,由于输出波长被锁定在光纤Bragg光栅的Bragg波长上,因此输出波长稳定,谱线窄,成本低.可应用于多波长干涉测量以及全光通信等领域中.     

Q-Switched Large-Mode-Area Yb-Doped Fibre Laser Using GaAs as Saturable Absorber

A passive Q-switched large-mode-area Yb-doped fibre laser is demonstrated using a GaAs wafer as the saturable absorber. A high Yb doping concentration double-clad fibre with a core diameter of 30μm and a numerical aperture of 0.07 is used to increase the laser gain volume, permitting greater energy storage and higher output power than conventional fibres. The maximum average output power is 7.2W at 1080nm wavelength, with the shortest pulse duration of 580ns and the highest peak power of 161W when the laser is pumped with a 25W diode laser operating at 976nm. The repetition rate increases with the pump power linearly and the highest repetition rate of 77kHz is obtained in the experiment.     

半导体激光器波长稳定系统的反馈效率

反射式体布拉格光栅(VBG)是改善半导体激光器(DL)输出光谱特性的首选器件。对快轴准直透镜(FAC)的非球面方程进行了数值拟合,采用光线追迹的方法建立了DL波长稳定系统反馈效率的计算模型,分析了FAC透镜、反射式VBG的空间位置和旋转角度变化对DL波长稳定系统反馈效率的影响,给出了波长稳定系统中FAC和反射式VBG的装调容差范围。分析结果表明:反射式VBG的空间位置偏差对反馈效率影响不大,但FAC透镜的空间位置和旋转角度偏差、反射式VBG的旋转角度偏差会造成反馈效率的急剧下降。     

A diode-pumped, frequency-doubled, tunable single-mode quasi-continuous-wave Yb:YAG laser emitting 70 W peak power at 515 nm

An efficient pumping scheme for a quasi-continuous-wave diode-pumped Yb:YAG laser is presented. Single-mode operation and fine wavelength tuning are assured by the use of a rubidium titanyl phosphate (RTP) Fabry–Perot étalon. When frequency doubled, the 200–420 μs duration pulses reach a peak power of 70 W at a wavelength of 515 nm. The TEM₀₀ beam is nearly diffraction limited with an M ² factor of 1.06 at full power. The tuning range spans from 512 to 520 nm and the pulse to pulse frequency stability is on the order of ±10 MHz. Laboratoire Aimé Cotton is associated with Université Paris Sud 11.