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The experimental setup was established for studying damage effects on silicon photoelectric detector materials induced by 800nm and 150fs repetitively-pulsed laser. The detector is irradiated by single shot and multiple shots respectively. The laser damage thresholds of silicon photoelectric detector material were measured. The surface morphologies of the material damaged by laser were analyzed. The surfaces damaged by laser with different energy were compared. The thresholds vary with the number of laser shots. According to the accumulation theory, the damage threshold is the power function of the shot number. Experimental results show that threshold of single shot that damages the silicon photoelectric detector is 0.156J/cm 2 . The laser damage threshold decreases with the increasing number of laser pulses, but the minimum value exists. The damage is mainly caused by the mechanical effect rather than thermal effect. In fact, the thermal effect during the interaction is so small that it can’t even be observed. Resistivity of the silicon photoelectric detector irradiated by femtosecond laser decreases and finally tends to a constant value.

Both scanning laser irradiation mode and the static mode can cause damage to the materials with different thresholds. In this paper, a simple criterion is derived theoretically to equate the threshold of static irradiation with the scanning one for flat-top laser so that the two damage threshold at different scanning velocity can be compared. The results of numerical simulations are in good agreement with the criterion, and the preliminary experiments verify the criterion.

The design and performance of a closed cycle, repetitively pulsed HF laser is described. The homogeneous glow discharge is formed with UV pre-ionization and transverse discharge structure. The optimal output parameters of single pulse operation are given by the investigation of discharge characteristics in SF6 /C2H6 gas mixture and output characteristics of laser pulse. The repetitively pulse energy stability of laser device are checked with different conditions of gas flowing velocity, charging voltage and total pressure of gas mixture. It is shown that the maximal output energy of laser pulse of 0.6J, peak power 3MW are obtained. Total efficiency of laser device is about 2.4%. When the gas mixture circulating with 4m/s flowing velocity, the maximal running frequency of 50Hz are obtained and operating stability keep well. Under these conditions, the laser pulse energy keeps stable and the average output power is 18W.

A special waveform of CCD being irradiated by intense laser is explained and simulated. Its specialty is that reference level is altered and becomes equal with saturated data level, which can answer for CCD’s black video induced by laser and named as excessive saturation effect. Alteration of reference level has been explained by signal charges injection into the measuring well during reference time. In CCD, wells barriers are largely lower than channel stop. After that all transfer wells are crammed, many remained signal charges getting rid of clock’s control can be hold in channel, and move along it in thermal diffusion and self-induced drift. They can fill up the measuring well ahead of clock’s permission and alter reference level to saturated data level. Based on the explanation, the waveform is simulated on an equivalent circuit of CCD’s charge measurement structure, which is built on the platform of Multisim2001. The voltage sources and switches are used to manipulate the charge and discharge of a capacitor, which simulates the charge injection and resetting of measuring well. The clocks controlling switches represent the injection and reset clocks in CCD. To simulate clock’s impact on output, other capacitor is used to connect it to capacitor that represents the measuring well. The equivalent circuit is validated by the simulated normal waveform. Then, altering the clock and charging the capacitor ahead, the excessive saturation waveform is simulated, which validates the explanation to excessive saturation effect.

A compact passively Q-switched and mode-locked erbium-doped fiber laser based on graphene saturable absorber was reported in this paper. A fiber ferrule, which had graphene deposited on the core region, was used as the saturable absorber. The Q-switched operation was initiated with a low pump threshold of about 50 mW at 974 nm and the repetition rate can be widely tuned from 14 kHz to 70 kHz along with the increase of the pump power. Moreover, the mode-locking state working at 1559.7 nm with a 0.4nm spectral bandwidth and about 3 ns pulse duration was also demonstrated in the same ring cavity when the pump power increased to about 150 mW. This is, to the best of our knowledge, the first report of the fiber laser, which had the both Q-switched operation with so wide repetition rate and mode-locking operation in the same ring cavity based on the same graphene saturable absorber.

A synthesis of the calorimetric and photoelectric method on the high energy laser beams measurement is presented. Data fusion of the two kinds of detector units is achieved with real-time scaling onsite. A set of compound diagnostic system is developed for the large area laser beam intensity distribution measurement, which is mainly composed of 256 calorimetric detectors, 120 photoelectric detectors, multi-channel data sampling module and one central processing computer. The total energy of the laser beam is accurately measured with calorimetric detectors, and the spatial intensity distribution with high temporal resolution is given by the photoelectric detectors. With the merits of energy accuracy and the temporal resolution based on the two kinds of detector units, the compound diagnostic system can be used to measure accurately the far-field temporal and spatial distribution of high energy laser beams.

Cross relaxation (CR) process in thulium ions is described. Performance of Tm-doped fiber lasers with different dopant concentrations is evaluated numerically with and without CR. Simulation shows that CR process can not only improve the slope efficiency and output of the laser system, but also lower the lasing threshold and extend the growth momentum of the laser performance. Backward LD-clad-pumped Tm-doped fiber lasers are built with Tm-doped fibers of different doping levels. A maximum output of 35.3W around 2μm is obtained with a slope efficiency of 47.2% from the 4.5wt.%- doped fiber laser while a higher slope efficiency of 54.1% was achieved from the 6.8wt.%-doped fiber laser. And, modeling shows that these laser systems are much more efficient than that without CR process.

Based on the invariable stretching stress preloading device, the experimental investigation on damage effect of 30CrMnSiA steel structure specimen by continuous laser was carried out. While the stress is between 660MPa and 1140MPa, the average laser power density is between 110W/cm 2 and 330W/cm 2 , we can get the conclusions as follow: (1) When the preloaded stretching stress increases, the necking phenomenon becomes unobvious. (2) When the preloaded stretching stress increases, both the rupture time and rupture temperature decrease monotonously. (3) When the laser power density increases, the rupture time decreases monotonously. (4) When the preloaded stretching stress or laser power density increases, the rupture threshold decreases monotonously. (5) The strain of the specimen before necking is small, and the specimen metamorphoses during necking period and the deformation of specimen is centralized in the necking region.

A method for direct laser beam diagnostics based on fiber array is introduced. The designing principle and configuration of the method are presented. The experimental results show that it can provide laser power density distribution information with a high spatial resolution better than 3mm and with an error of measurement less than 3%. The theoretical analysis by finite element method(FEM) for laser radiation indicates that this method should be used to measure the high energy laser beam with diameter of several hundred millimeters for tens of seconds. In addition, the results of fiber array technique are compared, qualitatively, with the spatial beam profile obtained by a near infrared charge coupled device(NIR-CCD). These two methods yield consistent results.

(ultraviolet). To generate strongly coupled plasmas (SCP) by high power excimer laser, an Au-CH-Al-CH target is used to make the Al sample reach the state of SCP, in which the Au layer transforms laser energy to X-ray that heating the sample by volume and the CH layers provides necessary constraints. With aid of the MULTI-1D code, we calculate the state of the Al sample and its relationship with peak intensity, width and wavelength of laser pulses. The calculated results suggest that an excimer laser with peak intensity of the magnitude of 10 13 W/cm 2 and pulse width being 5ns - 10ns is suitable to generate SCP with the temperature being tens of eV and the density of electron being of the order of 10 22 /cm -3 . Lasers with shorter wavelength, such as KrF laser, are preferable.

This paper presents the results of studies on high power photochemical XeF(C-A) laser with repetition mode. A new design of optical pumping source is proposed and the deposition efficiency is higher than 75 %. The form process and the temporal and spatial characteristics of the XeF 2 photodissociation wave are studied experimentally. The results indicate that when the deposition power is 12.5 MW/cm, the maximum brightness temperature reaches more than 25 kK and the photon flux obtained more than 4×10 23 photon s -1 cm -2 in the VUV range of 130 nm~180 nm. A novel XeF(C-A) laser which can be operated in repetition mode has been developed based on surface discharge optical pumping technique. The ideal output energy results of 20 laser pulses are presented under different repetitive rates and their optimal experimental conditions. Output energies of more than 4J and better stability can be obtained when the laser device operates at 1, 2 and 5 Hz, respectively. When the gas feed rate is larger than 53L/s, the average energy of 20 laser pulses is up to 3.2J at the repetitive rate of 10Hz. The technology for the laser spectral narrowing is studied.

The output energy stability of discharged-pumped pulsed HF laser in repetition rate mode is studied experimentally, and the optimal operating conditions are obtained. The experimental results show that the output energy decreases quickly with the increase of repetition rate, and increasing gas flow rate is beneficial to improve the discharge stability and the output energy stability as well. By optimizing the operating conditions, the laser can operate stably at the repetition rate of 50 Hz, with the stable output energy of about 260 mJ, and the average power is about 13 W.

In this paper, measuring results of laser scattering from rough aluminum samples by using integrating spheres are presented. The aluminum samples are diamond-turned to different roughness with random and periodic roughness distribution. The total integrated scattering (TIS) is measured to represent the scattering properties of rough surface. From the experimental results, we can conclude that the TIS value for random roughness distribution agrees well with Beckmann theory, while the measuring data for periodic roughness distribution don’t show such agreement.

A Tm-Ho codoped fiber saturable absorber based passively Q-switched fiber laser with a subsidiary pump is built. The repetition rate improvement with a subsidiary pump is observed. The average increases of the repetition rate are about 1 kHz and 1.5 kHz with a 15 mW and 20 mW subsidiary pump, respectively. A maximum repetition rate of 28.2 kHz is obtained with a 20 mW subsidiary pump. Simulations are carried out, validating the repetition rate improvement capacity of the subsidiary pump method.

The development of XeF(C-A) lasers by optical pumping in Northwest Institute of Nuclear Technology during recent 10 years is described in this paper. A joule level of XeF(C-A) laser optically pumped by a sectioned surface discharge was studied with the total efficiency of 0.1%. A more efficient XeF(C-A) laser was developed with the maximum outpup energy of 18.6 joules by two-side optically pumping and repetition mode operating.

A special designed long pulse XeCl MOPA laser system and its initial laser-target experiments are introduced. Laser produced plasmas of carbon, aluminum and copper are concerned. Based on measured results of plasma spectra and framing pictures of ejected plume, Plasma temperature and expanded speed of plasma flume are obtained.

A 250 J/210 ns four-stage XeCl laser system named Photons has been developed. Five lasers in MOPA chains characterized by different pumping techniques are described. Also, the main experimental results of the Photons are given.© (2005) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

A new heuristic optical scintillation model developed recently is viewed and it is a available method in investigation on laser beams propagation in turbulent atmosphere. The irradiance scintillation is treated as a modulation of small scale scintillation by large scale scintillation as laser beams propagation in turbulent atmosphere, the irradiance scintillation is investigated for uplink propagation at various receiving heights and zenith angles for different atmospheric turbulence model. The influences of receiving height and zenith angle on the irradiance scintillation is analyzed for different atmospheric turbulence model, and the conclusions deduced are useful for farther future researches.

A theoretical model concerning the Tm–Ho codoped fiber saturable absorber based passive Q-switching of an Er-doped fiber laser is established. Comparison with the Tm-doped fiber saturable absorber is described and discussed. Numerical results indicate that, compared with a Tm-doped fiber saturable absorber, the Tm–Ho codoped fiber saturable absorber shortens the lifetime of the 3F4 energy level and improves the operation of the laser system.

Laser-direct-driven ramp compression experiments were performed on long temporally shaped laser pulses based on an analytical isentropic compression model. Upper pressure limits, the ablation pressure scaling law, and stress-density curves were studied. The validity of the analytical model used, the ablation pressure scaling law, and the phenomena of missing line-imaging velocity interferometer (VISAR) fringes in the experimental results are discussed.

A characteristic method has been developed using a Murnaghan-form isentropic equation and characteristics, which has been verified by example uses. General information of two ramp compression experiments was calculated, which matched experimental ones well except for some tiny distinctions. Finally, the factors influencing the precision of this model were discussed and other practical applications were presented.

An all-fiber Q-switched Er-doped laser is built with a ring cavity. Stable Q-switching is demonstrated with a Tm–Ho co-doped fiber saturable absorber. The maximum repetition rate of the laser system reaches 42 kHz, which is much larger than that with Tm singly doped fiber saturable absorbers. Analysis shows that interaction between thulium and holmium ions is the main reason for this high repetition rate operation.

Exploiting a piece of 0.2 m long Tm–Ho codoped fiber as the saturable absorber, we demonstrate a wideband wavelength tunable passively Q-switched Er-doped fiber laser. The Tm–Ho codoped fiber has a wide absorption band around 1550 nm, promising wideband Q-switching of Er-doped fiber lasers. With a Fabry–Perot tunable filter, stable passive Q-switching is observed in a wide wavelength range from 1535 to 1573 nm. The repetition rate of the laser system is tunable with both the pump power and the lasing wavelength in the range between 0.5 and 50 kHz.

Gain-switched Tm?Ho Co-doped single clad fiber lasers are investigated with in-band pumping. The output ratio and cavity length are varied to investigate their impacts on the output pulses. The shortest pulse is 83.4?ns with a peak power of 10.5?W generated from the 3?m long laser cavity with 50% output ratio. At high pump pulse energies, gain-switched mode-locking operation is observed with a mode-locking repetition rate of tens of MHz, determined by the cavity length. The duration of the mode-locked pulse is no longer than 10?ns.

Pumped by a 1550 nm fiber laser, a gain-switched Tm/Ho co-doped single-clad fiber laser is built with a linear cavity. Stable gain-switching is achieved with the repetition rate ranging from 2 to 150 kHz. The highest peak power is 11.1 W with a pulse duration of 130 ns. Increasing the pulse energy of the pump, gain-switched mode-locking is attained with a sub-pulse repetition rate of 20 MHz and a pulse duration of about 10 ns; the peak power of the gain-switched envelope is about 4.6 W.

Mode-locking operation of an Er-doped fiber laser with a Tm?Ho co-doped fiber saturable absorber is demonstrated for the first time. Q-switching, Q-switched mode-locking and CW mode-locking operation modes are observed sequentially with increase of the pump power. In the mode-locking operation mode, a repetition rate at the fundamental cavity frequency of 9.05?MHz is obtained with a pulse duration of 46.3 ns. By rotating the polarization controller, a repetition rate up to 887?MHz is achieved, and the pulse duration is shortened to 0.548?ns.

An LD-clad pumped Tm-doped fiber laser is built with two multimode double-clad fiber Bragg gratings (FBGs) to generate narrow linewidth output around 2??m. The slope efficiency of this laser system is 43.1% with respect to the launched pump power, corresponding to a quantum efficiency of 109%, which means that at least 9% of the doped thulium ions take part in the two-for-one cross relaxation process. Exploiting two multimode FBGs and wrapping the fiber onto an aluminum spool, a single peak narrow linewidth spectrum is generated. A 3?dB linewidth of 57?pm centering at 1996.2?nm is obtained at an output of 3.6?W.