Crystal Growth and Laser Characteristics of Nd^(3+)∶KGd(WO_4)_2

The Nd^3＋ 3.2% （atom fraction）：KGd（WO4）2 crystal was grown by Kyropoulos method. The absorption spectrum and fluorescence spectrum of Nd^3 ＋ ： KGW crystal were measured. The absorption cross sections at 808 nm（0. 6799 × 10^-20 cm^2） were calculated, and the output wavelength of fluorescence is 1064 and 1351 nm. The diode-pumped laser was operated both in the free-running and passively Q-switched operating modes. The maximum laser output（1064 nm） is 326 mW with 62.7 % slope efficiency when input energy is 900 mW. The beam quality factor M^2 ≈ 1.1. The green light of 532 nm is obtained in frequency doubling operation. The laser is passively Q-switched by using Cr^4＋ ：LuAG as saturable absorber. The pulse width is 170 ns at repetitive frequency of 15 kHZ.

Doppler shift of a laser pulse beam scattered by a rotating cone and cylinder

Based on laser radar equations, a Doppler shift model of a laser pulse beam scattered by a rotating arbitrary convex target is reported in this paper. The boundary relations between an incident pulse beam and the detected area elements are analyzed by geometric methods. The Doppler shift characteristics of the rotating cone and cylinder are discussed and the difference between the laser pulse beam and the plane wave scattered from the same rotating target is compared accordingly. Numerical simulations show that the Doppler shift is tightly relevant to their dimensions, speeds, and so on. In the same incidence conditions, the pulse beam and plane wave have difference peak values and the same Doppler shift bandwidth. If the waist radius of the pulse beam is larger, the peak value is higher, and the Doppler shifts are proportional to the speed of the rotating target. By virtue of our theoretical model, we probe into the scattered characteristics of the Doppler shifts of a laser pulse beam, which would benefit target identification in national defense.

KGW晶体的1.06μm激光特性研究

In recent years,from the laser experimental study of neodymium doped potassium g adolinium tungstate,i.e.KGd(WO 4) 2 (KGW),laser scientific workers had discove r ed that it has many advantages,as compared to YAG and other tungstate crystals u n der indentical experimental conditions,such as low lasing threshold,high output energy o r power and high efficiency et al.Especially,as seen on the absorption spectra o f Nd:YAG and Nd:KGW reported by V.Kushawaha et al,a strong and broad absorption line around 808nm is much wider (～12nmFWHM) in Nd:KGW as compared to the Nd:YAG (～1.5nm FWHM),and this wavelength is just during the main peak area emitted by diode laser,so that Nd:KGW may be a excellent candidate for efficient diode pum ping at 808nm.Therefore the research and development of KGW crystals and laser d evices has been bestowed great attention in interational laser science area.For the laser rod with dimensions of  5mm×8mm and  6.3mm×75mm,the xenon flashlamp pumping KGW laser have achieved more laser output and higher efficie n ies than the YAG crystals under identical experimental conditions,by V.Kushawaha et al.In Unite State and K.A.Stankov et al.in Germang respectively.

Recent Advances in New Band Rare-earth Doped Fiber Amplifiers

Broadband,high bit rate,long hauls and system intelligence are current trends in developing fiber optic communication systems.The ever-increasing traffic demands have made it urgent to develop new band optical fiber amplifier.Laser characteristics of various rare-earth ion including Er3+,Tm3+,Pr3+,Dy3+,Ho3+,and Nd3+ doped fiber are reviewed.Recent advances of rare-earth doped fiber amplifiers with wide-band and flat gain are also introduced.

Computational fluid dynamic modeling of gas flow characteristics of the high-power CW CO_2 laser

To increase the photoelectronic conversion efficiency of the single discharge tube and to meet the requirements of the laser cutting system, optimization of the discharge tube structure and gas flow field is necessary. We present a computational fluid dynamic model to predict the gas flow characteristics of high-power fast-axial flow CO2 laser. A set of differential equations is used to describe the operation of the laser. Gas flow characteristics, are calculated. The effects of gas velocity and turbulence intensity on discharge stability are studied. Computational results are compared with experimental values, and a good agreement is observed. The method presented and the results obtained can make the design process more efficient.

The Effect of Lateral Guiding Mechanism on Noise Characteristics in Semiconductor Lasers

A comparison between intensity noise spectra and also the line shapes of gain-guided, weakly-index-guided, and strongly-index-guided semiconductor lasers are made using numerical solution of Maxwell-Bloch equations including spontaneous emission noise.

Characteristics Measurement of AFLM-Grating Cavity WDM Fiber Laser

In this paper, we study an FLM-grating cavity WDM fiber laser with dynamic polarization compensation technique for maintaining the output polarization states. We observe the characteristics and obtain the optimal experimental results.

Growth and spectral characteristics of a new promising stoichiometric laser crystal: Ca_9Yb(VO_4)_7

A Ca9Yb（VO4）7 crystal with dimensions of Φ23 mm×35 mm was grown successfully by Czochralski method. Its thermal conductivity was 1.06 W/（m？K） at room temperature. The absorption cross-sections at 980 nm were 1.80×10–20 cm2 and 1.28×10–20 cm2 for π- and σ- polarizations, respectively, with a full-width at half-maximum of 34 nm. The crystal had a broad emission at around 1025 nm with a full-width at half-maximum of 67 nm for π- polarization and 70 nm for σ- polarization. The emission cross-sections of the crystal were calculated by using reciprocity method and Füchtbauer-Ladenburg formula. The emission cross-sections at 1025 nm were 3.57×10–20 cm–2 and 1.91×10–20 cm–2 for π- and σ- polarization, respectively. The fluorescence lifetime was 332 μs. The results indicated that the crystal is a promising femtosecond and tunable laser material.

Cavity tuning characteristics of orthogonally polarized dual-frequency He-Ne laser at 1.15 μm

The cavity tuning characteristics of orthogonally polarized dual-frequency HeiNe laser at 1.15 μm are presented. Vectorial-extension model based on semi-classical laser theory reveals that cavity tuning characteristics are related to beat frequency, relative excitation, and type of Ne isotope. Distortions of cavity tuning curves become moderate with the increase of beat frequency because of the weakening of the cross- saturation effect. Distortions are enhanced with the increase of relative excitation because of the combined action of the self-saturation and cross-saturation effects. By adopting dual-isotope Ne instead of monoisotoplie Ne, distortions are reduced because of the misalignment between peaks of the self-saturation and net gain coefficients. The theoretical calculations are in good agreement with the corresponding experimental results.

Laser beam characteristic for laser resonators with diffraction optical elements

The matrix eigenvalue method is used to analyze a laser resonator composed of diffraction optical elements. The results show that this type of resonator can separate fundamental mode and high order modes effectively. The output beams can be designed for different requests.

Synthesis and Absorption Characteristics of Two Infrared Cyanine Dyes

Two infrared dyes, 1,3,3,1′, 3′, 3′ hexamethylindotricarbocyanine iodide (A) and 1,3,3,1′,3′,3′ hexamethyl 11 chloro 10,12 propylenetricarbocyanine iodide (B), were synthesized and characterized by melting point, elemental analysis, IR, and 1 H NMR. Their electron absorption spectra, laser absorption characteristics and solubility were investigated. The results showed that A and B have maximum absorption peaks at around 748nm and 774nm, respectivey, which match well with the wavelength output of the near infrared laser diode. The dyes were found to have photoinduced fading during irradiation with the infrared laser, especially in the presence of oxygen. However, this procession can be greatly slowed by using a layer of poly(vinyl alcohol) to barricade the dyes from oxygen. The experiments also showed that the dyes were thermally stable but decayed under strong sunlight. Furthermore, they are easily dissolved in some common solvents.