Development of a Lyman-α laser system for spectroscopy and laser cooling of antihydrogen

Hydrogen Lyman-α radiation (121.56 nm) is important because it allows for the excitation and detection of ground-state hydrogen atoms by a one-photon process. The trapping of antihydrogen, recently reported by the ALPHA collaboration at CERN, has revived interest in Lyman-α lasers. In order to perform high precision tests of matter-antimatter symmetry violations or gravity-antimatter interactions with antihydrogen, laser cooling using the 1s ? 2p single photon transition is essential. Recent theoretical simulations predict that even with a pulsed Lyman-α source, laser cooling of antihydrogen would be possible. Here we describe the implementation of a high power vacuum-ultraviolet (VUV) laser at the Lyman-α transition of hydrogen. The VUV light was generated using a two-photon-resonant four-wave mixing process in a phase-matched mixture of krypton and argon. Two wavelengths (ω _R → 202.31 and ω _T → 602.56 nm) were mixed in a sum-difference scheme (ω _VUV = 2ω _R ? ω _T ) with a two-photon resonance at (4s ²4p ⁵5p[1/2]₀ ← 4s ²4p ⁶(1S ₀)) transition in Kr. With an Ar/Kr mixture of 3.9:1 we obtained 10 ns pulses of 0.1 μJ of energy at a repetition rate of 10 Hz.     

Investigation of laser diode face-pumped high average power heat capacity laser

The three-dimensional (3D) pump intensity distribution in medium of the laser diode (LD) pumped high average power heat capacity laser is simulated by the ray tracing method, and the divergence characteristics of fast axis and slow axis of LD are simultaneously considered. The transient 3D temperature and stress distributions are also simulated by the finite element method (FEM) with considering the uneven heat source distribution in medium. A LD face-pumped Nd:GGG heat capacity laser is designed. The average output power is 1.49 kW with an optical-optical efficiency of 24.1%.     

Preparation of nanodiamonds by laser irradiation of graphite

Graphite powders were irradiated by pulsed laser at room temperature and normal pressure and then boiled in perchloric acid. Samples were characterized by high-resolution transmission electron microscopy (HRTEM), electron diffraction pattern (EDP), X-ray diffraction (XRD) pattern, and Raman spectroscopy. The analyses on the HRTEM images, EDP, and XRD show that the diamond particles with a size of about 5 nm are obtained. The shifting and broadening of the diamond peak in Raman spectrum indicate that there are high defect density and residual internal stress in synthetic diamond.     

X α studies of laser crystals

This paper reports the spin-polarized self-consistent-charge discrete variational (SCC-DV-X ) calculations for the garnets GGG(Ca, Mg, Zr), GGG, YGG and YAG. The calculated values of 10Dq for these garnets are reported for the first time, and are in good agreement with the experimental values. The relation between the calculated values and the distances of the central ion and the ligand ions is discussed. The energy values of the doublet state² E _g were also obtained, and the reason why YAG:Cr³⁺ only emits sharp fluorescence whereas GGG(Ca, Mg, Zr):Cr³⁺ can also emit strong broad fluorescence are explained.     

Comparison of laser performance of electro-optic Q-switched Nd:YAG ceramic/single crystal laser

An electro-optic Q-switched Nd:YAG ceramic laser operating at kHz repetition rate was demonstrated. Thermal induced lens' focus of ceramic rod was measured and compensated by plano-convex cavity structure. Depolarization loss at different output powers was measured in Nd:YAG single crystal and ceramic lasers. High-energy high-beam-quality laser pulse output was obtained in both laser structures. Pulse energy of about 20 mJ and pulse width of less than 12 ns were achieved, and the average power reached 20 W. The divergence of output laser beam was less than 1.2 mrad, and the beam propagation factor M2 was about 1.4.     

Theoretical study on the laser gain of a multi-stage dye laser amplifier

Theoretical studies on laser gain of a multi-stage dye laser amplifier are presented in this paper. The resultsshow that the influences of amplified spontaneous emission(ASE)and nonlinear absorption of excited-state on the gain are different for different input laser energies and gains. A threshold input intensityexists for a specific system. If the imput intensity is higher than the threshold, the nonlinear absorptionof excited-state will be the main cause for gain decrease. Otherwise, the ASE is the main cause. A newscheme is proposed to calculate the gain of the amplifier by the comparison of the input intensity with theeffective saturation intensity and the choice of the calculation gain method.     

Practical application of pulsed “eye-safe” microchip laser to laser rangefinders

The paper describes practical application of pulsed microchip laser generating at 1535-nm wavelength to a laser rangefinder. The complete prototype of a laser rangefinder was built and investigated in real environmental conditions. The measured performance of the device is discussed. To build the prototype of a laser rangefinder at a reasonable price and shape a number of basic considerations had to be done. These include the mechanical and optical design of a microchip laser and the opto-mechanical construction of the rangefinder.     

Low-power multi-pulse laser annealing of α-Ge

In this paper we want to show by means of Reflection High Energy Electron Diffraction (RHEED) techniques that the recrystallization processes taking place on amorphous germanium films irradiated with low-power superimposed ruby laser pulses occur gradually. Furthermore, in implanted α-Ge films the amorphous-crystalline front moves from the surface of the specimen towards the substrate, while the opposite occurs for glow-discharge deposited films. Moreover, electron microscope observations carried out with a double-stage carbon replica technique at different depths in the specimen show that defect migration is one of the competitive mechanisms in low-power laser annealing.     

Preparation of enamel coating by laser irradiation

Enamel coatings is produced on steel substrates using CW CO_2 laser irradiation from the same raw material as used for industrial enamel coating. The formed coating fairly well join to the substrate and has a bumpy glossy surface. Its microstructure is uniform and glassy with a liitle of small pores. It contains less Na and K than the initial composition. Fe element has been transfered into the coating, the content is high in the interface zone and low in the main body. This distribution may be at a time establish the good chemical stability of coating and its strong adhension to substrate. The present investigation also makes comparison of the laser irradiated coating with the ordinarily enamelled one.     

Quasi-continuous wave laser operation of Titanium-doped sapphire

The quasi-continuous wave Titanium-doped sapphire laser pumped by a frequency-dou-bled YAG laser developed in Tianjin University has been achieved new advance. An linear laser resonator consists of a reflecting mirror and an output coupler.The re-flecting mirror had dielectric coating of 100% reflectivity,and the output coupler is with 7%transmissibility.The laser rod was 21mm long and cut at Brewster's angle.     

Comparison of different side-pumping configurations for high power laser diode pumped solid-state laser

Ray-tracing method is used to simulate the distribution of absorption in crystal rod for different side-pumping configuration. The distribution of pumping power and absorption efficiency is compared, and the numerical results are presented. The results show that the more uniform pumping and the higher absorption coefficient are obtained with a diffuse cavity. And the method of the slow axis of laser diode stack perpendicular to the axis of lasing gives the higher central pumping density.     

Photothermal damage prediction of laser interstitial thermotherapy

An improved scattering optical model was developed under cylindrical coordinate to simulate the thermal effect of diffusing applicator in laser interstitial thermotherapy (LITT). The thermal damage was calculated by finite element method (FEM) using Pennes bio-heat transfer equation and Arrhenius injury integral formula. The numerical results showed that the scattering can considerably influence the evaluation of the lesion area, and the relationship between application powers or time and resulting tissue thermal damage was nonlinear. Although usually applying relatively low power can avoid tissue charring, rather higher power is recommended because it is indispensable to achieve necessary damage threshold and the therapy time can be shortened.     

Coherent laser spectroscopy of ¯pHe+

The facilities of the coherent laser pulse spectroscopy of the ¯pHe⁺ transitions are considered taking the magnetic structure of the energy levels into account. The possibility for the observation of the dynamics of intramolecular motions is also analyzed.     

Deposition of nanoparticles during laser ablation of nanoparticle-containing targets

We analyze the morphology of ablated nanoparticles after their laser-induced deposition on various substrates. We show that, at moderate laser intensity of the 210 ps pulses on the surface of nanoparticle-containing materials (<5×10⁹ W?cm^?2), the deposited material remains approximately the same as the initial nanoparticles. We compare these deposited nanoparticles with the debris obtained by the laser ablation of bulk material of the same origin as nanoparticles at different intensities of laser radiation. The presence of nanoparticles in laser plumes allowed for analyzing high-order nonlinear optical properties of nanoparticles. The efficient high-order harmonic generation was achieved during propagation of femtosecond pulses through such plasmas.     

Ultrashort-pulse laser irradiation of metal films: the effect of a double-peak laser pulse

The optical properties of blue-violet InGaN light-emitting diodes under normal and reversed polarizations are numerically studied. The best light-emitting performance under normal and reversed polarization is obtained in a single quantum-well structure and double quantum-well structure, respectively. The key factors responsible for these phenomena are presumably the carrier concentration distribution and the amount of carriers in quantum wells. The turn-on voltage of light-emitting diodes under reversed polarization is lower than that of light-emitting diodes under normal polarization, due mainly to lower potential heights for electrons and holes in the active region.     

Possible generation of a γ-ray laser by electrons wiggling in a background laser

The possibility of γ-ray laser generation by the radiation of wiggling electrons in a usual background laser is discussed.     

Applications of laser in the field of chemical solubility determination

A novel experiment method for chemical solubility determination was brought forward, in which optics and chemistry principles are united and the change of laser intensity indicates the process of chemical dissolving. The more undissolved solid exists in the mixture of solute and solvent, the less transmitted laser intensity is detected. Only when the transmitted laser intensity in stirring state and that in static state comes into equalization, the dissolving process stops. Under the help of laser intensity judgement, measurements turn to be more feasible and objective, especially at high pressure. The average relative errors for the solubility data determined in this paper are 2.3% for those in the minor value scope and 1.7% for those in the high value scope respectively. Comparison of the experimental solubility data with the literature ones demonstrates that the laser-aid solubility determination apparatus is stable and reliable.     

Optimization of linear cavity design of Yb-doped double-clad fiber laser

The output characteristics of a linear cavity Yb-doped double-clad fiber (DCF) laser, including the effects of fiber length, fiber loss, and output mirror reflectivity on laser output power and threshold pump power have been studied theoretically and experimentally. In this paper, the linear cavity of double-clad fiber laser (DCFL) was composed of a pair of fiber Bragg gratings, while the facet of fiber was anti-reflection (AR) coated at 1070nm to erase the Fresnel reflection. Analysis showed that the laser output increases as     

Characteristics of laser and current pulses in a He–SrCl2 vapor laser

An experimental investigation on the characteristics of laser and current pulses in a He–SrCl₂ vapor laser is carried out. The temporal dependences of the discharge current pulse on the laser pulses at the 1.09 μm, ～3 μm and 6.45 μm lines in strontium atoms and ions are measured and analyzed under different laser output powers. It is found that all laser pulses appear at the falling edge of the current pulse and shift forward to the current pulse with increasing laser output power.     

Discharge instability induced by external laser preionization of a XeF discharge laser

External-laser-induced preionization of excimer lasers was investigated. A discharge XeF laser was preionized by two different UV lasers [a KrF laser (λ=249 nm) and an ArF laser (λ=193 nm)], and the improvements in performance of the XeF laser were compared. The XeF laser beam profiles were measured by an intensified CCD (ICCD) camera with temporal resolution of 10 ns. Striated XeF laser profiles were obtained with 249 nm laser preionization, whereas there was no striation in the profiles for 193 nm laser preionization. These striations originated from discharge in the XeF laser induced by laser preionization. The influence of excited rare-gas atoms on the discharge instability was examined.