Cross-relaxation dynamics on anomalous saturation processes in low pressure supersonic cw HF chemical laser amplifier

It is assumed that both translational and rotational noneq ui librium cross-relaxations play a role simultaneoulsy in low pressure supersonic cw HF chemical laser amplifier. For two-type models of gas flow medium with la minar and turbulent flow diffusion mixing, the expressions of saturated gain spe ctrum are derived respectively, and the numerical calculations are performed as well. The numerical results show that turbulent flow diffusion mixing model is i n the best agreement with the experimental result.

Kinetics analysis of chemiluminescence in discharge-driven HF chemical lasers

The chemiluminescence spectrum in the optical cavity of discharge-driven hydrogen fluoride （HF） chemical laser is measured. The result reveals that the spectra of the helium and fluorine （F） atoms are the major components. Moreover, the green chemiluminescence in the downstream of the optical axis is mostly composed of the 60P20 spectral line of the HF molecule. The analysis shows that, except for the cold pumping reaction, the recombination of the F atoms and the hot pumping reaction also occur in the optical cavity. Due to the hot pumping reaction and the opticM cavity temperature in a specific range, the 60P20 line becomes the strongest HF molecule in the downstream region of the optical axis. After the hot pumping reaction, the green chemiluminescence always appears in the downstream region of the optical axis when the optical cavity temperature varies in a ~reater ran~.

Numerical study on the performance of nozzle flow for supersonic chemical oxygen-iodine lasers

Laser performance is greatly dependent on its operating conditions due to the strong coupling among multi- physics such as gas-dynamics, chemical reaction kinetics and optics in the mixing nozzle of COIL. In this paper, 3D CFD technology is used to simulate the mixing and reactive flow of subsonic cross jet scheme at different conditions. Results obtained show that the jet penetration depth plays a dominant role in the spatial distribution of small signal gains. In the case of over-penetration, unsteady flow structures are induced by impinging between the opposing jets. The optimum spatial distribution of the chemical performance cannot be obtained even if the full penetration condition is achieved through the subsonic transverse jet mixing scheme in the COIL nozzle flow.

Development of Electrospray Laser Chemical Vapour Deposition for Homogenous Alumina Coatings

Electrospray,as a liquid source supply system,has been applied to chemical vapour deposition（CVD）.In thermal CVD,the microstructure of the obtained films changes from dense to coarse granular because of the decreasing surface temperature during deposition.Using the electrospray laser chemical vapour deposition method,we prepared homogenous alumina coatings.We found that laser irradiation was effective in compensating the surface temperature decrease,and an alpha-alumina coating with dense columnar microstructures was obtained at a deposition rate of 200 μm/h using 200 W Nd：YAG laser irradiation.

Fabrication of Through Micro-hole Arrays in Silicon Using Femtosecond Laser Irradiation and Selective Chemical Etching

We demonstrate a method of fabricating through micro-holes and micro-hole arrays in silicon using femtosecond laser irradiation and selective chemical etching. The micro-hole formation mechanism is identified as the chemical reaction of the femtosecond laser-induced structure change zone and hydrofluoric acid solution. The morphologies of the through micro-holes and micro-hole arrays are characterized by using scanning electronic microscopy, The effects of the pulse number on the depth and diameter of the holes are investigated. Honeycomb arrays of through micro-holes fabricated at different laser powers and pulse numbers are demonstrated.

PERFORMANCE AND MICROSTRUCTURE OF SUPERHARD Si_3N_4 FILM BY HIGH POWER CO_2 LASER CVD

A superhard α-Si_3N_4 film,deposited on metal substrate,was produced by laser chemical vapor deposition adopting a kW-level high power CO_2 laser.Most films are composed of fine Si_3N_4 partieles.They join the metal substrate in strong bond.The films have super hardness,excellent resistance to wear and corrosion,etc.Their thickness may be controlled within 5-30 μm.

A Kilowatt Radio-Frequency Excited Diffusively Cooled All-Metal Slab Waveguide CO2 Laser

A new type of rf excited diffusively cooled all-metal slab waveguide CO2 laser is presented, in which the waveguide channel is constructed by two copper side walls and two copper electrodes, and the discharge is confined in the slab waveguide channel in terms of the voltage division structure. From this type of structure, over 1 kW laser power is obtained with an efficieney of more than 13%.

Phase retarder in chemical oxygen-iodine laser at 45° incidence

A phase retarder used in chemical oxygen-iodine laser （COIL） system has been fabricated by ion beam sputtering （IBS）. When the incident angle is 45°the reflectivity is about 99.9% from 1290 to 1340 nm and about 83.8% at 632.8 nm, and the phase retardance between the parallel and perpendicular polarization components is -92.8°at 1315 nm. In order to get the influence of temperature on the phase retarder, six samples have been annealed from 523 to 648 K at interval of 25 K in air respectively, and the results show good temperature performance, With increasing temperature phase retardance becomes smaller, and the variation is within 4° at 1315 nm. At the same time, the variation maintains within ±10° for the incidence from 44°to 49°.

Preparation of rutile TiO_(2) thin films by laser chemical vapor deposition method

TiO_(2) thin films were prepared on Pt/Ti/SiO_(2)/Si substrate by laser chemical vapor deposition(LCVD)method.The effects of laser power(P_(L))and total pressure(p_(tot))on the microstructure of TiO_(2) thin films were investigated.The deposition temperature(T_(dep))was mainly affected by P_(L),increasing with P_(L) increasing.The single-phase rutile TiO_(2) thin films with different morphologies were obtained.The morphologies of TiO_(2) thin films were classified into three typical types,including the powdery,Wulff-shaped and granular microstructures.p_(tot) and T_(dep) were the two critical factors that could be effectively used for controlling the morphology of the films.

Efficient pulsed chemical oxygen-iodine laser with instantaneous generation of atomic iodine by volumetric discharge

A pulsed chemical oxygen-iodine laser （COIL） using atomic iodine generated by volumetric discharge of CHaI is developed and tested. COIL with a gain length of 60 cm is energized by a square pipe-array jet singlet oxygen generator with basic hydrogen peroxide pumping circulations and operated at subsonic gas flow. Maximum output energy of 4.3 J, pulse duration of 50 #s, specific energy extraction from the active medium of 2.0 J/L, and the maximum chemical efficiency of 12.5% are achieved at a chlorine flow rate of 55 mmole/s.

02（1△） Yield Measurement by Raman Spectroscopy With Elimination of Chlorine Fluorescence Interference

Deleterious chlorine fluorescence was found to occur at the same frequency as the Raman scattering of 02 （1 A） and 02 （3 E）, seriously affecting the 02 （1 A） yield measurement in the reaction of chlorine with basic hydrogen peroxide by use of the Raman spectroscopy technique. To solve this problem we have taken advantage of the fact that Raman radiation is always strongly polarized while fluorescence is essentially non-polarized in a gaseous medium. When chlorine utilization of a singlet oxygen generator is 88%, 02（1A） yield reaches （42.4±7.4）% with the effect of chlorine fluorescence completely eliminated.

Few-layer MoS2 grown by chemical vapor deposition as a passive Q-switcher for tunable erbium-doped fiber lasers

We report an erbium-doped fiber laser passively Q-switched by a few-layer molybdenum disulfide（MoS2） saturable absorber（SA）.The few-layer MoS2 is grown by the chemical vapor deposition method and transferred onto the end-face of a fiber connector to form a fiber-compatible MoS2 SA.The laser cavity is constructed by using a three-port optical circulator and a fiber Bragg grating（FBG） as the two end-mirrors.Stable Q-switched pulses are obtained with a pulse duration of 1.92 μs at 1560.5 nm.By increasing the pump power from 42 to 204 mW,the pulse repetition rate can be widely changed from 28.6 to 114.8 kHz.Passive Q-switching operations with discrete lasing wavelengths ranging from 1529.8 to 1570.1 nm are also investigated by using FBGs with different central wavelengths.This work demonstrates that few-layer MoS2 can serve as a promising SA for wideband-tunable Q-switching laser operation.

Preparation of TiO_(2)-rich Ba-Ti-O thick films by laser chemical vapor deposition method

TiO_(2)-rich Ba-Ti-O films were prepared on Pt/Ti/SiO_(2)/Si substrate by laser chemical vapor deposition(LCVD).Their phase relationship and microstructure were investigated.The single-phase BaTi_(2)O_(5),Ba_(4)Ti_(13)O_(3)0 and BaTi_(5)O_(11) films were prepared at Ti/Ba molar ratios m_(Ti/Ba)=1.84-1.90,2.83 and 4.49-4.55,respectively.The high deposition rate of TiO_(2)-rich Ba-Ti-O films ranged from 54.0μm/h to 177.6μm/h.The permittivity of BaTi_(2)O_(5)film(prepared at m_(Ti/Ba)=1.84 and deposition temperature T_(dep)=877 K),Ba_(4)Ti_(13)O_(3)0 film(prepared at m_(Ti/Ba)=2.83 and T_(dep)=914 K)and BaTi5O11 film(prepared at m_(Ti/Ba)=4.49 and T_(dep)=955 K)were 50,40 and 21,respectively.

Air Stability of Cs2CO3：Ag/Ag Cathode for Organic Light-Emitting Diodes

We report the superior stability of the composite Cs2CO3 ：Ag/Ag cathode structure, which can be used in efficient organic light-emitting diodes （OLEDs）. Devices with the Cs2CO3：Ag （1：10, 5nm）/Ag （95nm） cathode show a considerably improved lifetime compared with the control device with the Cs2CO3 （0.5 nm）/Ag （100 nm） cathode. The composite Cs2CO3 ：Ag/Ag film is proved to be stable in the atmosphere. X-ray diffraction （XRD） is applied to analyze the crystalline structure of the Cs2CO3：Ag film, and it is demonstrated that CsAg alloy is formed, leading to the improved stability of the thin film and the devices.

Antibacterial Action of Chemically Synthesized and Laser Generated Silver Nanoparticles against Human Pathogenic Bacteria

Silver nanoparticles in the range of 10-40 nm were synthesized chemically and by laser ablation, em- ployed for in vitro antibacterial action against human pathogenic bacterium. Their formation was evidenced by UV-visible spectrophotometer; particle size confirmed by atomic force microscopy, crystal structure determined by X-ray diffraction and chemical composition investigated by Fourier transform infrared spec- troscopy. The calculated MIC （minimum inhibitory concentration） of chemically synthesized nanoparticles with 30-40 nm in size are 2.8 μg/mL 4.37 μg/mL 13.5μg/mL and 2.81 p.g/mL for E. coil, S. aureus, B. subtillis and Salmonella, respectively. Whereas laser ablated nanoparticles exhibit MIC of 2.10 μg/mL 2.36 μg/ mL and 2.68 μg/mL for E. coli, S. aureus and Salmonella, respectively.

Photoinduced Reorientation Process and Nonlinear Optical Properties of Ag Nanoparticle Doped Azo Polymer Films

Azobenzene polymer films doped with and without Ag nanoparticles are prepared. The photoinduced reorientation process is investigated by using an Nd：YVO4 pump beam at 532 nm and a low semiconductor laser beam at 650 nm. The reorientation rate of azo polymer films is enhanced in the presence of Ag nanoparticles, and the rate of the azo polymer film with Ag concentration of 2.2 μg/ml is larger than that of the azo polymer films with Ag concentrations of 1.1 μg/ml and 4.4 μg/ml. The third-order nonlinear optical properties of the Ag/azo composite film are obtained by the Z-scan technique at a wavelength of 532 nm, and the measured nonlinear refractive index is 9.258×10-9 esu. It is shown that the main mechanisms involved in the large nonlinear optical responses come from the local field enhancement of Ag nanoparticles and the nonlinear effect of the azo polymer matrix.

Absorption measurement of optical thin films under high power density with a Closed Cavity

A Closed Cavity measuring platform is built on the basis of a 1000 W-class direct current （DC）-discharge drived con- tinuous-wave （CW） HF/DF chemical laser. On this platform, the absorption coefficients of optical thin films coated on the surfaces of monocrystalline silicon substrates, at the wavelength of 3.6-4.1 μm, is measured, when the power density on the surfaces of optical thin films reaches about 3.16 kW/cm^2. The measuring principle and structure of the Closed Cavity is introduced. The temperature curves and balanced temperature rises of the film-suN strate systems under test measured through the experiment is presented in this Letter. The experiments show high reliability, good repeatability and strong practicality. The Closed Cavity measuring platform is applicable for not only absorption measurement but other performance measurement of optical thin films under high power density.