ZnO random laser spectra under nanosecond pumping

Spectra of ZnO random lasers were obtained using a Peltier-cooled CCD camera Videoscan-285 at a single shot of nanosecond pumping. It was demonstrated that these spectra differ essentially from lasing spectra under picosecond pumping: as a rule, the line widths are significantly larger and the spectra often change essentially from shot to shot in a random manner on the same pumping spot. We suggest that large line widths can be the result of many lasing acts appearing during a single pumping pulse and of the lasing frequency changing in every lasing act. The random variations of spectra from shot to shot can be called forth by spontaneous emission fluctuations.     

Low-threshold lasing in stimulated Raman lasers with nanosecond pumping

We have studied the conditions resulting in maximum lowering of the excitation threshold for pulsed stimulated Raman (SRS) lasers. It has been shown theoretically that in order to achieve the lowest possible values of laser radiation pulse energy needed to excite lasing in SRS lasers, we need high reflection of the cavity mirrors and low losses at the wavelength of the 1st Stokes component, high reflection of the output mirror at the wavelength of the pump radiation, and also matching of the confocal parameters for the exciting laser radiation and the cavity with each other and with the length of the Raman-active medium. The experimentally achieved excitation threshold for an SRS laser based on a barium nitrate crystal was 6 μJ, which quantitatively corresponds well to the calculation results. Lasing of up to five Stokes components simultaneously occurred. The efficiency for conversion of the laser radiation to one component was as high as 39%. __________ Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 75, No. 2, pp. 284–290, March–April, 2008.     

Development of precise nanosecond and picosecond dye lasers for spectroscopy of antiprotonic atoms

Two laser systems were developed by the ASACUSA collaboration of CERN to carry out spectroscopy experiments on antiprotonic atoms. One of these was a continuous-wave pulse-amplified dye laser which was frequency-stabilized to a femtosecond frequency comb. The other generated 700-ps-long laser pulses of wavelengths λ?=?266 and 532 nm using two stimulated Brillouin scattering cells filled with water.     

Simple generation of 400–700 nm picosecond dye laser pulses with nanosecond laser pumping

New results in the experimental study of the spectro-temporal selection (STS) method to produce picosecond dye laser pulses are presented. Adjustability of the picosecond pulse wavelength, possibility of extension of the STS method to different dyes and to UV pump wavelength, stability of the output pulse duration and intensity, and the concentration effect on pulse duration, are reported for the first time. From these results, production of high power picosecond (50–100 ps) dye laser pulses spectrally adjustable between 400 and 700 nm is obtained with a standard nanosecond pump laser, in a compact and simple device.     

双光子抽运随机激光器中辐射光能量的演化

基于非相干反馈随机激光器的扩散方程理论，将扩散方程中的增益项改写为饱和形式，并利用有限差分方法，研究了双光子抽运随机激光器中辐射光能量随时间演化特性.对扩散方程的数值求解给出了系统辐射光能量由自发辐射开始，经历小信号增益状态得到放大，再到由于增益饱和形成稳态输出的整个演化过程.表明介质的无序导致了在较低能量情况下也能获得饱和增益这样的非线性效应.结果为研究获得双光子抽运随机激光器的稳态输出提供了理论依据. 关键词： 随机激光器 双光子抽运 饱和效应 无序介质中的光学效应     

Generation and amplification of nanosecond pulses by iodine lasers

Results are reported of experimental investigations of high-power photodissociation iodine laser pumped by lamps and by radiation from high-current electric discharges. The basic parameters of the working medium, the parameters of both lamp-pumped and discharge-pumped lasers, and methods of shaping of a short pulse with diffraction directivity of the radiation are investigated. The possibility of effective amplification of a short pulse by an iodine amplifier pumped with an open high-current discharge is demonstrated. An iodine laser generating a pulse of duration I nsec, divergence 10^-4 rad, and energy 100 J at a contrast 10⁸ and 300 J at a contrast 10²–10³ is described.Translated from Trudy Ordena Lenina Fizicheskogo Instituta im. P. N. Lebedeva, Akademii Nauk SSSR, Vol. 125, 46–103, 1980.     

Femtosecond,picosecond and nanosecond laser ablation of solids

Laser ablation of solid targets by 0.2–5000 ps Ti: Sapphire laser pulses is studied. Theoretical models and qualitative explanations of experimental results are presented. Advantages of femtosecond lasers for precise material processing are discussed and demonstrated.     

Characterization of organic material micro-structures transferred by laser in nanosecond and picosecond regimes

The laser-induced forward transfer technique has been performed on thin layers of conducting organic materials for applications in plastic micro-electronics.This process is a promising alternative for fabrication of organic electronic components on flexible supports when usual techniques, such like ink-jet printing, cannot be considered. For example, when the organic material has no solubility properties or when complex architectures are needed.Experiments on the influence of pulse duration (nanosecond and picosecond) and wavelength on a large range of fluences have been proceeded using different lasers. An optimization of the process has been carried out by inserting a thin layer of absorbing metallic material between the substrate and the organic film. The advantage of this technique is to preserve organic layers from being damaged by thermal and photochemical effects during the interaction.The morphology and thickness of the deposit have been investigated by optical and scanning electronic microscopy. This experimental study is supplemented by electrical characterization of the deposits.     

微微秒叶绿素染料激光器的研究

本文报道用一台对撞脉冲锁模Nd:YAG激光器的三倍频光作为泵浦光源,采用超短腔结构,获得叶绿素的红色ps脉冲激光输出的装置和实验结果。研究了叶绿素a和b在各种聚合状态下输出激光波长随染料浓度的变化关系,当叶绿素a-乙醇溶液浓度为2×10~(-3)M,激光腔长<36μm时可获得单模调谐ps系列脉冲输出,激光束的发散角≈60mrad。     

Recording of dynamic holograms by nanosecond and picosecond laser pulses in solid-state fullerene-containing matrices

The results of a complex investigation of the recording of dynamic holograms by pulsed radiation with a duration of 20 ns and 300 ps in fullerene-containing media based on porous glasses and polymethyl methacrylate matrices are reported. Spectral analysis of these media in the range 300–700 nm was performed. The efficiency of hologram recording was found to relate with the occurrence of a band at 330 nm in the absorption spectrum of a medium. It is shown that dynamic holograms can be recorded in the fullerene-containing media by nanosecond and picosecond pulses. In the latter case, holograms arise mainly due to a change in the electronic polarizability of fullerene molecules, which is almost inertialess. The results obtained can be used in the development of ultrafast switching devices based on dynamic holograms.     

Nonlinear optical properties of an azo-based dye irradiated by picosecond and nanosecond laser pulses

The nonlinear optical properties of an azo-based dye were investigated using Z-scan technique employing 38 ps pulses at 532 and 1064 nm, and 6 ns laser pulses at 532 nm. Large nonlinear absorption and nonlinear refraction were observed at both ps and ns 532 nm in the azoic dye. When excited at ps 1064 nm, this dye displayed a large two-photon absorption cross-section (σ₂=1810 GM). Meanwhile, the optical nonlinearity mechanism was discussed in terms of molecular structure, excitation wavelength, and pulse width.     

Absorption and gain of laser dyes with picosecond pumping

Using a passively mode-locked Nd:YAG laser, the absorption and gain of oxazine 1 and 9 were examined. Picosecond pumping is shown to have better gain efficiency and wavelength tunability than nanosecond pumping.     

Detection of picosecond laser pulses with nanosecond time resolution by use of analogue-to-digital converters

A photodetector-analogue-to-digital converter system with 1.8 ns rise and decay time is described. The photodetector waveform is fanned-out with power splitters and sampled with high-speed analogue-to-digital converters. The system is used to detect picosecond light pulses from a mode-locked Nd-glass laser with nanosecond time resolution.     

System for nanosecond and picosecond laser synchronization using high-voltage semiconductor switches

Results are presented on the development and investigation of a system for the synchronization of the emission of a nanosecond laser, used for plasma heating, with the emission of a diagnostic picosecond laser. The system is based on the use of the fast-semiconductor-switch technology, and ensures a temporal synchronization instability not higher than 100 psec.Laser-Plansma Laboratory and Special Design Office. Lebedev Physics Institutes, Academy of Sciences of the USSR. Translated from Preprint No. 85 of the Lebedev Physics Institute, Academy of Sciences of the USSR, Moscow, 1988.     

Two-photon fluorescence bioimaging with an all-semiconductor laser picosecond pulse source

We have demonstrated successful two-photon excitation fluorescence bioimaging using a high-power pulsed all-semiconductor laser. Toward this purpose, we developed a pulsed light source consisting of a mode-locked laser diode and a two-stage diode laser amplifier. This pulsed light source provided optical pulses of 5 ps duration and having a maximum peak power of over 100 W at a wavelength of 800 nm and a repetition frequency of 500 MHz.     

Characteristic properties of ZnO random laser pumped by nanosecond pulses

Investigations of UV radiation spectra of powdered zinc oxide and its unordered film were conducted. The samples were pumped by 3-rd harmonics of the two-stage Nd:YAG-laser (λ=355 nm) with pulse duration ∼10 ns. Maximum density of energy of pumping pulses was about 150 mJ/cm². With some of our samples, we achieved lasing. The threshold values of the pumping energy density occurred higher than those under picosecond pumping approximately for one-two orders of magnitude. It was shown that the threshold of lasing and the character of lasing spectra depend on the morphology of particles forming a powder. The long-wavelength shift of the maximum of lasing spectra with a rise of the pumping was observed. It was interpreted as a result of participation of electron–hole plasma recombination in the process of lasing. A chaotic character of lasing spectra was observed and partially analyzed. PACS 42.55.Zz; 78.55.Et; 42.70.Hj