Laser-diode-pumped 1319-nm monolithic non-planar ring single-frequency laser

Single-frequency 1319-nm laser was obtained by using a laser-diode-pumped monolithic Nd:YAG crystal with a non-planar ring oscillator (NPRO). When the NPRO laser was pumped by an 800-μm fiber coupled laser diode, the output power of the single-frequency 1319-nm laser was 220 mW, and the slope efficiency was 16%. With a 100-μm fiber coupled diode laser pumped, 99-mW single-frequency 1319-nm laser was obtained with a slope efficiency of 29%.     

Enclosed laser ablation of 20 nm aluminium films using a continuous wave diode laser: II—Theoretical heating considerations and proposed mechanisms

Laser ablation using a 120 W continuous wave diode laser was carried out upon a thin aluminium layer which had been hermetically sealed between two layers of polymer. The results (presented in Part I) have shown that the film could be partially transparentised but with an efficiency which was far less than that seen for a Q-switched laser. In this paper, the thermal effects within the films are analysed and a mechanism by which enclosed surface laser ablation occurs is proposed.     

High-power 390-nm laser source based on efficient frequency doubling of a tapered diode laser in an external resonant cavity

We frequency doubled the single-frequency beam from an external-cavity tapered laser diode operating at 780 nm in a resonant cavity containing a beta -barium borate crystal to generate an output at 390 nm with high efficiency. Output powers as great as 233 mW were obtained, corresponding to an efficiency of 65%/W . The resonant-cavity design was a low-loss three-mirror configuration that provided compensation for astigmatism and coma. The laser diode frequency was locked to the doubling-cavity resonance by use of the H?nsch-Couillaud discrimination technique.     

半导体激光器激活层中的四波混频和相位共轭光的发生

本文提出了一种从半导体激光器中发生和检测相位共轭光的新方法,并用1.3μm分布反馈半导体激光器作了实验验证。本方法不仅可以用来发生相位共轭光,还可以用来研究振荡运转中的激光激活介质的非线性光学特性。     

Ablation of subsurface tumors using an ultra-short pulse laser

This paper demonstrates the novel technique of ablating subsurface tumors with minimal thermal damage to surrounding healthy tissue using a focused laser beam from an ultra-short pulse diode laser source. Experiments were performed on anesthetized healthy mice as well as mice with mammary tumors in order to demonstrate the fundamental advantages of using a focused-beam, ultra-short pulse laser to ablate subcutaneous tissues. The technique was demonstrated through histological analysis of tissue samples after irradiation of anesthetized mice with or without mammary tumors. To demonstrate the efficacy of subsurface focusing, temperature was monitored at the subsurface tumor location and at the surface in an untranslated sample while irradiating with a focused ultra-short pulsed 1552 nm laser. Results show that temperature rise was dramatically greater at the focal depth than at the surface. Irradiation at the subsurface tumor location while translated over time across the tumor location resulted in precise ablation of the tumor. This work shows that a focused-beam ultra-short pulse 1552 nm laser results in precise ablation at the desired location with high efficacy and a minimal zone of collateral thermal and/or mechanical damage.     

Fabrication of a random convex-lens-shaped microstructure using a laser ablation

A convex-lens-shaped microstructure with a diameter of 50 μm on a metallic mold substrate was fabricated in this paper. A laser ablation process, in which the laser beam was focused and irradiated on the metallic mold substrate in order to remove a part of the substrate, was used for that. The convex-lens-shaped microstructure has not been reported in any studies of microstructure using the laser ablation process. It was proposed that the unbalanced ablation and re-adherence of the melted particles was the processing mechanism of the convex lens shape. The convex-lens-shaped microstructure fabricated in this study is smaller than the focused spot. It was expected that the same convex-lens-shaped microstructure can be fabricated even if the focused spot size is increased, so long as the fluence of the laser can be maintained. Therefore, the method proposed in this paper will improve the low processing speed, which has been the problem of a laser ablation process. The fabricated convex-lens-shaped microstructure on the metallic substrate can be used as the mold for the micro lens.     

The study of a Tm:YLF laser pumped by a Raman shifted Erbium fiber laser at 1678 nm

A Tm:YLF laser pumped by a Raman shifted Er-fiber laser at 1.678 μm was studied at two Tm³⁺ ion concentrations equal to 1.5% and 5%. At output powers up to 460 mW the measured lasing efficiency at a wavelength of ~ 1.93 μm was as high as ~ 50%. The lasing performance was compared with that obtained under pumping by a 792-nm laser diode. The temporal structure of the laser pulse was recorded and the beam propagation factor M² was measured for all pumping conditions.     

Measurement of thermal rise-time of a laser diode based on spectrally resolved waveforms

Thermal resistance and thermal rise-time are two basic parameters that affect most of the performances of a laser diode greatly. By measuring waveforms received after a spectroscope at wavelengths varied step-by-step, the spectrally resolved waveforms can be converted to calculate the thermal rise-time. Basic formulas for the spectrum variation of a laser diode and the measurement set-up by using a Boxcar are described in the paper. As an example, the thermal rise-time of a p-side up packaged short-pulse laser diode was measured by the method to be 390 μs. The method will be useful in characterizing diode lasers and LD modules in high-power applications.     

Influence of scanning velocity on bovine shank bone ablation with pulsed CO2 laser

The influence of scanning speed on hard bone tissue ablation is studied with a 10.6-μm laser. The groove morphology and the thermal damage created in bovine shank bone by pulsed CO2 laser are examined as a function of incident fluence by optical microscope following standard histological processing. The results show that ablation groove width, depth and ablation volume, as well as the zone of thermal injury, increase gradually with incident fluence. As compared to the result for high scanning speed, the lower scanning speed always produces larger ablation volume but thicker zone of thermal injury. It is evident that scanning speed plays an important role in the ablation process. In clinical applications, it is important to select appropriate scanning speed to obtain both high ablation rates and minimal thermal injury.     

激光烧蚀对碳纳米管薄膜场发射性能的影响

采用丝网印刷工艺制作了碳纳米管(CNTs)薄膜阴极.经适当能量激光烧蚀后,相互粘连的CNTs随表面粘附有机物的蒸发而分散开,管间隙增加、屏蔽效应减小,使得场发射性能大幅度提高,开启场强降低、场倍增因子β增大.Raman光谱分析表明,随激光能量增加,CNTs表面缺陷增多,成为新的场发射点,对其β增大的贡献加强.相对于两电极结构,三电极中平栅极结构场发射性能经激光烧蚀有更显著的改善.这说明激光烧蚀是提高CNTs场发射性能的有效方法. 关键词： 碳纳米管薄膜 场发射 激光烧蚀 Raman光谱     

预脉冲在毛细管快放电软x射线激光中的作用

在一台毛细管快放电软x射线激光实验装置上，在相同主脉冲条件下（电流峰值18—30kA，半周期80ns），通过观测放电产生的软x射线辐射，研究了该装置固有的高幅值（2—5kA）和外加的低幅值（10—20A）两种预脉冲，对聚乙烯毛细管和高纯度陶瓷毛细管（99.9%）放电的管壁烧蚀及等离子体状态的影响.采用装置固有的几kA预脉冲和聚乙烯毛细管，放电 过程中产生了大量的管壁烧蚀，并且这种情况下的等离子体均匀性差，没有可能获得激光输 出.而采用20A的预脉冲和高纯度陶瓷毛细管，管壁烧蚀量大大减少，预电离等离子体的均匀 性好，在这种情况下，实验上利用x射线二极管观测到了激光尖峰信号. 关键词： 预脉冲 毛细管放电 软x射线激光     

阵列半导体激光器的光束参数测量与光纤耦合

采用ISO推荐的方法测量了发光面为 1μm× 15 0 μm的阵列半导体激光器的光束半径、远场发散角、束腰位置、瑞利长度 ,并根据测量结果计算了光束传输因子 (M2 因子 )。以此为基础 ,研究了半导体激光器光束的快轴准直以及光纤耦合技术 ,采用微柱面透镜准直后 ,阵列半导体激光器快轴方向发散角可减小到 0 .48°。设计了光纤耦合光学系统 ,与 10 0 μm光纤耦合时的耦合效率为 71.0 % ,与 2 0 0 μm光纤耦合时的效率为 83.4%。     

Damage/ablation morphology of laser conditioned sapphire under 1064 nm laser irradiation

The damage/ablation morphologies and laser induced damage threshold (LIDT) of three different sapphire samples: original, 1064 nm laser conditioned and 10.6 μm CO₂ laser polished substrates are investigated with ns pulses laser irradiation. The results indicate that the damage resistance capability cannot be enhanced by 1064 nm laser conditioning or CO₂ laser polishing. The damage/ablation morphology of 1064 nm-laser conditioned samples is same as that of the original sapphire. But it is different from the damage/ablation morphology of the CO₂ laser polished sapphire. The “gentle and strong” ablation phases are observed in this work and several phenomena are observed in the two ablation phases. Ripple is observed in the “gentle” ablation processes, while convex spots and raised rims are observed in the “strong” ablation processes. Meanwhile, stripe damage and pin-points are observed in the CO₂ laser conditioned sapphire after ns laser irradiation. The formation mechanisms of the phenomena are also discussed for the explanation of related damage/ablation morphology. The results may be helpful for the damage/ablation investigation of sapphire in high power laser systems.     

高功率二极管激光器寿命测试

 介绍了高功率激光二极管不同模式的失效机理，分析了激光二极管不同的寿命测试方法；在冷却水温20℃和实际工作温度下分别对封装的激光器进行了寿命测试。根据试验结果得出退化率，推算出准连续二极管激光器在水温20℃，电流90A，占空比为10%（500Hz，200μs）时，平均激光工作寿命为2.19×10⁹次脉冲；冷却水温35℃时，其平均激光工作寿命下降为1.65×10⁹次脉冲。由实验结果分析得出，高功率激光器封装工艺中的焊料沉积和多层焊接技术，以及工作环境温度是影响激光器可靠性和寿命的关键因素。     

Low phase noise diode laser oscillator for 1S-2S spectroscopy in atomic hydrogen

We report on a low-noise diode laser oscillator at 972?nm actively stabilized to an ultrastable vibrationally and thermally compensated reference cavity. To increase the fraction of laser power in the carrier we designed a 20?cm long external cavity diode laser with an intracavity electro-optical modulator. The fractional power in the carrier reaches 99.9%, which corresponds to an rms phase noise of φ(rms)2=1?mrad2 in 10?MHz bandwidth. Using this oscillator, we recorded 1S-2S spectra in atomic hydrogen and have not observed any significant loss of the excitation efficiency due to phase noise multiplication in the three consecutive two-photon processes.     

UV laser irradiation of IR laser generated particles ablated from nitrobenzyl alcohol

Particles generated by 2.94 μm pulsed IR laser ablation of liquid 3-nitrobenzyl alcohol were irradiated with a 351 nm UV laser 3.5 mm above and parallel to the sample target. The size and concentration of the ablated particles were measured with a light scattering particle sizer. The application of the UV laser resulted in a reduction in the average particle size by one-half and an increase in the total particle concentration by a factor of nine. The optimum delay between the IR and UV lasers was between 16 and 26 μs and was dependent on the fluence of the IR laser: higher fluence led to a more rapid appearance of particulate. The ejection velocity of the particle plume, as determined by the delay time corresponding to the maximum two-laser particle concentration signal, was 130 m/s at 1600 J/m² IR laser fluence and increased to 220 m/s at 2700 J/m². The emission of particles extended for several ms. The observations are consistent with a rapid phase change and emission of particulate, followed by an extended emission of particles ablated from the target surface.     

Experimental femtosecond laser photodisruption of rabbit sclera for minimally invasive laser sclerostomy: An in vitro study

Femtosecond laser technology, used as a minimally invasive tool in intrastromal refractive surgery, may also have potential as a useful instrument for glaucoma filtration surgery. The purpose of the present study was to evaluate the feasibility of minimally invasive laser sclerostomy by femtosecond laser photodisruption and seek the appropriate patterns of laser ablation and relevant laser parameters. A femtosecond laser (800 nm/50 fs/1 kHz), focused by a 0.1 numerical aperture (NA) objective lens, with different pulse energies and exposure times was applied to ablate hydrated rabbit sclera in vitro. The irradiated samples were examined by scanning electron microscopy (SEM). By moving a three-dimensional, computer-controlled translation stage to which the sample was attached, the femtosecond laser could produce three types of ablation patterns, including linear ablation, cylindrical aperture and rectangular cavity. With pulse energies ranging from 37.5 to 150 μJ, the linear lesions were consistently observed at the inner surface of sclera, whereas it failed to make any photodisruption if pulse energy was below the threshold value of 31.25 μJ, with the corresponding threshold intensity of 4.06×10¹⁴ W/cm². The depths of the linear lesions increased linearly with both pulse energy (37.5–150 μJ) and exposure time (0.1–0.4 s). Histological examination showed the incisions produced by femtosecond laser photodisruption had precise geometry and the edges were sharp and smooth, with no evidence of collateral damage to the surrounding tissue. Our results predict the potential application of femtosecond laser pulses in minimally invasive laser sclerostomy for glaucoma treatment.     

Diode end-pumped passively Q-switched Nd:YAG ceramic laser with Cr4+:YAG saturable absorber

We report on a diode end-pumped passively Q-switched Nd:YAG ceramic laser. By using a Cr⁴⁺:YAG single crystal with an 80% initial transmission as the saturable absorber, stable Q-switched pulses with a 126-μJ pulse energy, a 12-ns pulse width, and an 8.4-kHz pulse repetition rate have been obtained. The Q-switching performance of the laser under different saturable absorption strengths and output couplings was experimentally investigated.     

High power AlGaInP laser diodes with zinc-diffused window mirror structure

The technology of zinc-diffusion to improve catastrophic optical damage (COD) threshold of compressively strained GaInP/A1GaInP quantum well laser diodes has been introduced. After zinc-diffusion, about 20-μm-long region at each facet of laser diode has been formed to serve as the window of the lasing light. As a result, the COD threshold has been significantly improved due to the enlargement of bandgap by the zinc-diffusion induced quantum well intermixing, compared with that of the conventional non-window structure. 40-mW continuous wave output power with the fundamental transverse mode has been realized under room temperature for the 3.5-μm-wide ridge waveguide diode. The operation current is 84 mA and the slope efficiency is 0.74 W/A at 40 mW. The lasing wavelength is 656 nm.     

Injection-seeded Tm:YAG laser at room temperature

The solid-state, tunable, narrowband, high pulse energy and high reliability lasers are attractive source for LIDAR system. In this paper, we demonstrated a diode pumped injection-seeded 2 μm Tm:YAG laser. By inserting two F-P etalons into the laser cavity, linear-polarized single-frequency seed-laser was achieved at a wavelength of 2013 nm, with a maximum output power of 60 mW. Long-term and short-term frequency stability for the seed-laser were 1.27 × 10^− 7 and 97 Hz/μs, respectively. High power Q-switched laser was operated using a bowtie cavity, the bidirectional output of which was favorable for the injection-seeded. After injecting the seed-laser to the power-laser, single-frequency, nearly transform-limited pulsed 2 μm laser was obtained. As much as 2.0 mJ output energy was achieved at an operating repetition rate of 15 Hz, with a pulse width of 356.2 ns.