Self-injection locking of an extraordinarily wide broad-area diode laser with a 1000-microm-wide emitter

The experimental results of self-injection locking of an antireflection-coated broad-area diode laser with a 1000-microm-wide emitting area are presented. To our knowledge, it is the broadest single-element diode laser that has been used in an external-feedback cavity until now. Usually, wide diode lasers suffer from filamentation, which leads to poor spatial beam quality. We show, however, that the beam quality of the diode laser is improved significantly when we use asymmetric self-injection locking. An output power of 2.05 W is obtained with a beam quality factor M2 of 2.7. The self-injection locking technique improves the beam quality by a factor of 107. By comparing the results with those obtained with an ordinarily coated diode laser with a 1000-microm-wide emitter we show that antireflection coating on the front facet is decisive for this improvement in the beam quality.     

Continuous-wave Raman generation in a diode-pumped Nd3+:KGd(WO4)2 laser

Continuous-wave Raman generation in a compact solid-state laser system pumped by a multimode diode laser is demonstrated. The Stokes radiation of stimulated Raman scattering at 1.181 microm is generated as a result of self-frequency conversion of the 1.067 microm laser radiation in Nd3+:KGd(WO4)2 crystal placed in the cavity. The Raman threshold was measured at 1.15 W of laser diode power. The highest output power obtained at the Stokes wavelength was 54 mW. The anomalous delay of Raman generation relative to the start of laser generation (the oscillation buildup) due to slow accumulation of Stokes photons in the cavity at low Raman gain and Raman threshold dependence not only on the laser intensity but also on the time of laser action are observed.     

大功率半导体激光器阵列热串扰行为

以硬焊料传导制冷,30%填充因子半导体激光器阵列为例,建立了三维有限元模型,对阵列内部各发光单元之间的热串扰行为进行了分析研究。结果表明,当其连续波工作时间大于1.2 ms后,阵列内发光单元之间出现热串扰现象;当次热沉由CuW合金改为铜金刚石复合材料时,阵列内发光单元自热阻和相邻发光单元的串扰热阻降低,有效地降低了各发光单元之间的热串扰行为。保持阵列宽度、发光单元数目及发光单元周期不变,发现随阵列填充因子的增加,器件热阻以指数衰减趋势逐渐降低,而发光单元间的热串扰特性对此变化并不敏感;保持阵列单个发光单元输出功率,发光单元尺寸及阵列宽度不变,增加发光单元个数后,阵列内各发光单元之间热串扰加剧,填充因子越高阵列升温速率越快;但在最初约70 s内,包含不同数目发光单元的阵列最高温度差异仅约0.5 ℃,有利于多发光单元高填充因子器件高功率输出。     

Power efficiency of a semiconductor laser with an external cavity

Optical feedback modifies the power vs. current diagram of a laser diode as well as its spectrum. Though optimization of the spectral characteristics is usually the main goal in the design of an external cavity source, power efficiency is also important, especially with relatively high power devices, where temperature variations due to dissipation can have an impact on the wavelength stability and on the laser lifetime. A useful parameter to describe the total power efficiency of the stabilized laser, relative to that of the solitary laser, is proposed in this paper. The dependence of this parameter on the characteristics of the active device, and of the external cavity, is investigated.     

Efficient quasi-three-level Nd:YAG laser at 946 nm pumped by a tunable external cavity tapered diode laser

Using a tunable external cavity tapered diode laser (ECDL) pumped quasi-three-level Nd:YAG laser, a fivefold reduction in threshold and twofold increase in slope efficiency is demonstrated when compared to a traditional broad area diode laser pump source. A TEM₀₀ power of 800 mW with 65% slope efficiency is obtained, the highest reported TEM₀₀ power from any 946 nm Nd:YAG laser pumped by a single emitter diode laser pump source. A quantum efficiency of 0.85 has been estimated from experimental data using a simple quasi-three-level model. The reported value is in good agreement with published values, suggesting that the model is adequate. Improvement of the 946 nm laser due to the ECDL's narrow spectrum proves to be less significant when compared to its spatial quality, inferring a broad spectrum tapered diode laser pump source may be most practical. Experimental confirmation of such setup is given.     

Wavelength tuning characteristics of a fabry-perot semiconductor laser with an external short cavity

Wavelength tuning characteristics of a Fabry-Perot semiconductor laser with an external short cavity are analyzed, in which the oscillation wavelength can be changed by slightly altering the external cavity length. Analysis is based on rate equations for an optical power and carrier density. It is shown that the wavelength tuning range is dominated by a change of carrier density through the effect of carrier-induced refractive index change in the active layer of a laser diode. This depends on effective coupling coefficients of the optical field iteratively reflected back to the laser diode by the external mirror, and on reflection coefficients of an anti-reflection coated laser facet and the external mirror which compose the external cavity. The effective coupling coefficient is also derived using the waveguide theory and Kirchhoff ’s theory. Finally, an unstable condition which may limit a stable wavelength tuning range is shown by results of a linear stability analysis of rate equations.     

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.     

Repetitively pulsed CO2 laser driven by an electron accelerator with a gas-discharge plasma cathode

A repetitively pulsed electron-beam-controlled CO₂ laser driven by an electron accelerator with a plasma electron emitter based on low-pressure glow discharge with hollow anode and cathode is presented. The application of the proposed emitter makes it possible to sharply increase the current and to control the electron-beam duration and, hence, the energy and time characteristics of the laser. It is demonstrated that the radiation pulse duration ranges from 300 to 1200 μs, whereas the radiation energy amounts to 200 J at an efficiency of 18%. In the course of lasing, the focal spot is not affected by the heterogeneous heating of the active medium. A significant heterogeneity in the gas flow upon an incomplete renewal of the gas in the zone filled with radiation leads to an increase in the focal spot owing to the wavefront distortions. Original Text ? Astro, Ltd., 2006.     

Frequency doubled diode laser in alternative extended cavity

We report on an alternative extended cavity scheme used with a 180 mW quantum well GaAlAs diode laser, operating near 850 nm. A dispersing prism and a thin glass plate are employed to enforce stable single-mode operation in the strong feedback regime, with no need for laser AR coatings. Compared to other configurations where a grating is used, the lower loss in the extended cavity allows higher fundamental power available for second harmonic generation. For example, by frequency doubling using potassium niobate in a power enhancement cavity, enough power can be generated from a single diode laser to decelerate and trap calcium atoms with radiation at 423 nm.     

Simplified model for calculation of power and spectral characteristics of laser diode with fiber Bragg grating

A simplified model consisting of a laser diode, air gap, and optical fiber is used to calculate power and spectral characteristics and the band width of the radiation of laser with fiber Bragg grating. The results of the simplified model are in reasonable agreement with the experimental data on power and spectral characteristics. The radiation band width of the laser diode with fiber Bragg grating can be less than the band width for a single laser diode by four orders of magnitude.     

Two-frequency lasing in the Nd:YLF laser with a lens-shaped active element and longitudinal diode pumping

In the laser with lens-shaped Nd:YLF [100] active element, the dependence of polarization and frequency of the radiation on the cavity length is studied under conditions of longitudinal diode pumping. The conditions at which birefringence in the Nd:YLF active element allows two-frequency lasing are determined.     

Wavelength Tuning Characteristics of a Vertival Cavity Surface Emitting Laser Diode with an External Short Cavity

The characteristics of a wavelength tunable vertical cavity surface emitting laser diode (VCSEL) with an external short cavity are analyzed, in which the oscillation wavelength can be changed over several tens of nanometers with a nearly constant optical power by slightly altering the external cavity length. Analysis is based on rate equations for the optical power and carrier density, taking the effect of carrier-induced refractive index change into consideration, together with the study of behaviors of a complex resonator. The reflection coefficient r₂ of a laser facet facing the external mirror is shown to affect notably the characteristics of wavelength tuning, optical power and carrier density for a change of the external cavity length. It is also noticed that the wavelength change for this length becomes slower with relatively larger r₂ due to an increasing contribution of the effect of carrier-induced refractive index change, within the optical gain spectrum of the laser diode.     

基于曲面空间合束的多单管半导体激光光纤耦合

随着单管半导体激光器光纤耦合技术的不断发展,为了进一步提高多单管半导体激光器的输出功率,本文采用曲面空间排列方式对多个单管半导体激光器进行合束研究,使更多数量的单管半导体激光器耦合进入同一光纤中,获得更高的输出功率。文中利用ZEMAX光学设计软件进行仿真模拟,将34只波长为975 nm、输出功率为10 W的单管半导体激光器合束聚焦后耦合进芯径200 μm、数值孔径0.22的光纤中,获得耦合效率91.76%、输出功率312.03 W的激光系统。实验中,将17只单管半导体激光器耦合进芯径200 μm、数值孔径0.22的光纤中,在10.5 A的驱动电流下,输出功率为100.5 W,系统耦合效率为68.46%。     

Computer Simulation of a 5.7GHz, 110kW Transit-Time Oscillator

A high-power transit-time oscillator producing 110kW at 5.7GHz in the TM₀₁₀ cavity mode is described. The device comprises a temperature-limited diode electron gun operating at 40A in the range from 28kV to 35kV and an intermediate coaxial cavity from which the microwave power is extracted through a TEM coaxial guide. The diode serves also as a resonant cavity, where electromagnetic oscillations are grown from noise. The effect of the applied voltage on both the output microwave power and the instability saturation time has been investigated leading to an optimal diode voltage of 33kV.     

Frequency-narrowed external-cavity broad-area-diode for rubidium laser pumping

Using an external cavity with holographic grating, we demonstrate the spectral narrowing of a high power broad-area-diode with a single emitter. The spectral bandwidth of less than 15 GHz is obtained with output power exceeding 10 W and external cavity efficiency exceeding 60%. Absorption of 98% of the laser radiation by a 25-mm rubidium vapor cell filled with 600-torr ethane at a temperature of 368 K is acquired, which demonstrates the availability of this pump source for efficient rubidium laser pumping.     

光栅外腔半导体激光器GHz射频调制特性研究

研究了光栅外腔半导体激光器(ECDL)对射频频率调制的响应特性,分析了射频频率调制时光栅外腔对半导体激光器的边带信号的影响.实验中测量了GHz射频频率调制的.ECDL输出的边带信号随射频信号功率、注入电流、光栅外腔长度的变化情况.证实了当射频调制频率等于光栅外腔自由光谱区的整数倍时,ECDL输出的边带信号可在一定程度上得到增强.     

1.3μmInGaAsP/InP涂层结构超辐射发光二极管输出特性的理论和实验

本文用考虑了增益饱和和热效应的耦合速率方程,对减反射涂层结构1.3μmInGaAsP/InP超辐射发光二极管的输出特性进行了计算,给出了腔长、有源层厚度和后腔面反射率对其输出光功率的影响以及光谱半宽随腔长和注入电流的变化。计算结果与我们制备的该结构超辐射发光二极管测试结果有较好的符合。     

Performance Characteristics of Power Build-Up Cavity for Raman Spectroscopic Measurement

Performance characteristics of power build-up cavity (PBC) as the light source of a Raman spectroscopy based gas sensor were studied. The key parameter to optimize stable and high intra-cavity power operation was beam diameter of the back reflected beam from external cavity to diode laser. The optimum diameter determined by an appropriate distance between the cavity and diode laser was found to be comparable with the waveguide cross section of diode laser for the effective spatial filtering, where inevitable cavity coupling loss caused by slight spatial mode mismatching existed. A PBC with a finesse of ∼10300 achieved a stable TEM₀₀ mode in excess of intra-cavity power of 80 watts pumped by a 10 milliwatts diode laser. Simultaneously, the PBC wavelength is found to be passively locked effectively at 670 +/− 0.15 nm where the center of the gain region exists. A Raman spectrum of nitrogen measurement was demonstrated.     

Improvement of the operation parameters for a Cr:LiSAF ultrashort-pulsed laser

The optimization of the pumping power that is focused on a gain medium inside an optical cavity is fundamental for increasing the efficiency of the power transferred inside a crystal, in this way increasing the output power of the laser. Nevertheless, in the case of pumping with a highly astigmatic laser diode, an undesirable form of the beam is focused on the cavity and the process to improve the cross section and sizes of the beam produce a notable reduction in the effective pump power ultimately focused in the crystal. The cavity design improvements for a Cr:LiSAF laser pumped with a 200 um × 1 um laser diode emission is presented for three different configurations, Z, V, and ring. The pump power is introduced in the cavity through a simple optical array, coupling more than 83% of the laser-diode power. The design requirements for the resonant cavity are reviewed in order to improve the coupling between the fundamental mode of the cavity and the cross-section form of the pumping beam. The stability limits of the cavities and Kerr sensitivity region are presented.     

High Repetition Rate Fiber Laser Coupled to a Linear Cavity Generating Picosecond Pulses

An experimental investigation is presented for obtaining picosecond (ps) pulses at a repetition rate of 11 GHz using a fiber laser coupled to an external cavity. Without applying active mode locking and without a nonlinear element in the coupled cavity, pulses of about 15 ps with an average power of 20 mW have been generated using a (cw) diode pump laser. The pulse duration decreases with increasing repetition rate.