High-efficiency 2 kW XeCl excimer laser

Received: 15 May 1998 / Revised version: 5 August 1998 / Published online: 24 February 1999     

All-fiber wavelength-swept laser near 2 μm

We report, for the first time to our knowledge, an all-fiber wavelength-swept Tm-doped laser based on a fiber Fabry-Perot tunable filter in the 2 μm spectral region. The laser wavelength can be continuously tuned over 200 nm from 1840 to 2040 nm in a short period of time. The demonstrated tuning speed was 12.5 μm/s with a tuning efficiency of 17.5 nm/V. The spectral linewidth of the laser was measured to be approximately 300 MHz or 0.01 cm(-1). This kind of laser can find potential applications in both high-resolution laser spectroscopy and tunable mid-IR generation via nonlinear frequency conversion.     

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.     

High power 4.65 μm single-wavelength laser by second-harmonic generation of pulsed TEA CO2 laser in AgGaSe2 and ZnGeP2

A high power 4.65 ??m single-wavelength laser by second-harmonic generation (SHG) of TEA CO₂ laser pulses in silver gallium selenide (AgGaSe₂) and zinc germanium phosphide (ZnGeP₂) crystals is reported. Experimental results show that the average output power of SHG laser is not only restricted by the damage threshold of the nonlinear crystals, but also limited by the irradiated power of fundamental-wave laser depending on the operating repetition-rate. It is found that ZnGeP₂ can withstand higher 9.3 ??m laser irradiation intensity than AgGaSe₂. As a result, using a parallel array stacked by seven ZnGeP₂ crystals, an average power of 20.3 W 4.65 ??m laser is obtained at 250 Hz. To the best of our knowledge, it is the highest output power for SHG of CO₂ laser by far.     

Free-running emerald laser pumped by laser diode

Free-running emerald laser pumped by 660-nm laser diode (LD) was reported. Free-running output power of 24 mW has been obtained with overall efficiency of 1.4% and slope efficiency of 11.9% when the LD incident power was 2.56 W. The laser threshold value of emerald crystal was estimated to be 0.7 W.     

Waveguide CW 118.6 μm H2O laser

This paper reports results of an experimental study of a cw 118.6 m H₂O waveguide laser. The laser cavity is a 3 cm inner diameter, 3.2 m long Pyrex tube, with plane reflectors against its ends, one of them being a copper mesh coupler. The active medium is a H₂O:H₂ gas mixture. Successive optimizations lead to a reliable output power of 50 mW, for the EH₁₁ mode. The power density is the highest ever reported, and the stability is such that the power drifts by less than 2% per hour. This laser is competitive with the optically pumped 118.8 m CH₃OH laser.     

CO2 gas resonance absorption at CO2 laser wavelength in?multiple laser coating

Multiple laser beams demonstrate many advantages as energy sources in diamond synthesis. In a reported amazingly-fast multiple laser coating technique, CO₂ gas is claimed as the sole precursor or secondary precursor for forming a diamond or diamond-like carbon, which remains poorly understood. The absorption coefficient changes under the irradiation of multiple lasers are one of the keys to resolve the mysteries of multiple laser beam coating processes. This study investigates the optical absorption in CO₂ gas at the CO₂ laser wavelength. The resonance absorption process is modeled as an inverse process of the lasing transitions of CO₂ lasers. The well-established CO₂ vibrational-rotational energy structures are used as the basis for the calculations with the Boltzmann distribution for equilibrium states and the three-temperature model for non-equilibrium states. Based on the population distribution, our predictions of the CO₂ absorption coefficient changes as a function of temperature are in agreement with the published data.     

Charateristics of a helical axial flow CO_2 laser

A novel CO_2 laser tube which forms a helical axial gas flow is designed. The influences of such a flow on the output laser beam is discussed.     

Graphene mode-locked femtosecond laser at 2 μm wavelength

We experimentally demonstrated a passively mode-locked femtosecond laser by using a graphene-based saturable absorber mirror (graphene SAM) in the spectral region of 2 μm. The graphene SAM was fabricated by transferring chemical-vapor-deposited, high-quality, and large-area graphene on a highly reflective plane mirror. Stable mode-locked laser pulses as short as 729 fs were obtained with a repetition rate of 98.7 MHz and an average output power of 60.2 mW at 2018 nm.     

Mathematical modelling of gain-switched RF-excited CO2 waveguide laser

The detailed mathematical models for the evolution of light pulses in RF-excited CO2 waveguide lasers are derived. Explicit expressions for the pulse characteristics in RF-excited CO2 waveguide lasers are obtained. The effects of losses and unsaturated gain on output power are calculated.     

Optical properties and CO_2 laser SHG with HgGa_2S_4

Optical properties and nonlinearity on phase-matching (PM) of two (yellow and orange) phase crystals were investigated in details. Damage threshold was determined in comparison with middle infrared (IR) crystal at identical experimental conditions. Second harmonic generation (SHG) of 30 ns TEA CO2 laser pulses was realized with 5% efficiency in energy and 6.9% in peak power.     

Quantum electrodynamics in a laser and the electron laser collisionQuantum electrodynamics in a laser and the electron laser collision

Quantum electrodynamics in a laser is formulated, in which the electron-laser interaction is exactly considered, while the interaction of an electron and a single photon is considered by perturbation. The formulation is applied to the electron- laser collisions. The effect of coherence between photons in the laser is therefore fully considered in these collisions. The possibility of y-ray laser generation by use of this kind of collision is discussed.     

Surface characteristics of SiO_2-TiO_2 strip fabricated by laser direct writing

SiO_2-TiO_2 sol-gel films are deposited on SiO_2/Si by dip-coating technique.The SiO_2-TiO_2 strips are fabricated by laser direct writing using an ytterbium fiber laser and followed by chemical etching.Surface structures,morphologies and roughness of the films and strips are characterized.The experimental results demonstrate that the SiO_2-TiO_2 sol-gel film is loose in structure and a shrinkage concave groove forms if the film is irradiated by laser beam.The surface roughness of both non-irradiated and laser irradiated areas increases with the chemical etching time.But the roughness of laser irradiated area increases more than that of non-irradiated area under the same etching time.After being etched for 28 s,the surface roughness value of the laser irradiated area increases from 0.3 nm to 3.1 nm.     

3W average power 4.3 μm CO2 laser

A 3 W average power CO₂ laser oscillating in the range of 4.3m (10°1 to 10°O transition) is described. At the same time, the laser can emit 100 W in the sequence band 00°2 to 10°1 (10.6m). It is based on a commercial system with continuous-wave discharge of 12 m length and a slow gas flow. It operates in the Q-switched mode at pulse repetition rates up to 15 kHz. The pulse peak power is 1 kW and the pulse duration is 200 ns. The deviation from the theoretical efficiency limit has been decreased by a factor 2.5 in our device, due to saturation of the pumping (sequence band) radiation. We predict an improvement by another factor of 5 (possible average power of 10 to 20 W), if one avoids the absorption in the discharge-free zones.     

RF excited diffusively cooled all-metal slab waveguide CO_2 laser

In this paper, a new type of radio frequency (RF) excited diffusively cooled all-metal slab waveguide CO2 laser is presented, in which the waveguide channel is constructed by two aluminum side walls and two aluminum electrodes, the discharge is confined in the slab waveguide channel in terms of the voltage division structure. From this type of structure, 127-W laser power is obtained.     

AnX α study of the laser crystal MgF2:V2+

The electronic structures of the laser crystal MgF₂:V²⁺ were obtained with the spinpolarized MS-X method. The calculated value of 10Dq and the energies of the lowest doublet states were given for the first time. The relations between the laser properties and the electronic structures were discussed.     

Multi-use laser impulse pendulum and laser propulsion parameters measurement

In order to investigate the mechanisms of both the air-breathing and the ablation modes of laser propulsion under laboratory conditions, a multi-use laser impulse pendulum (MULIP) is developed. The measurable impulse range is from 1.0×10-4 to 3.8×10-3 N·s. The experimental calibration data agree well with the theoretical calculated data. With MULIP, the ablation mode has been performed, in which a high power pulsed Nd:glass laser (λ= 1.06μm, τ=20 ns) and a gray PVC film sample are used. The experimental results show that the maximum momentum coupling coefficient Cm is 7.73×10-5 N/W, and the maximum specific impulse Isp is 208.6 s.     

Gain dynamics of the 4.3 μm CO2 laser

A detailed study of the gain dynamics of the pulsed, optically pumped 4.3 m CO₂ laser is described. Small-signal gain coefficients as high as 14%/cm are measured in a 4.3 m amplifier using low-power pulses from a 4.3 m probe laser. The measurements are compared with a rate-equation model and good quantitative agreement is obtained. The model, which uses no adjustable parameters, is described in detail. Gain is studied as a function of optical pumping power, gas mixture, gas pressure and discharge excitation of the 4.3 m amplifier. Optimization of the gain is discussed.     

Spectral–kinetic characteristics of the F2 laser transition

A theoretical model for the F₂(D–A) laser transitions is built. The model includes a scheme of the main laser transitions proposed. A value of the radiative lifetime of the upper laser level in the conventional kinetic models of the F₂ laser is proved to be underestimated by one order of magnitude. A general theory of steady-state light amplification in a molecular laser with non-equilibrium vibrational distribution is developed. Relations of the small-signal gain and the saturating energy flux with parameters of molecular electronic–vibrational kinetics are established. The theory is applied to explain properties of F₂ laser amplifiers. PACS 31.70.Hq; 42.55.Lt     

Yb:CaF2 — a new old laser crystal

Here is presented and discussed the history, the spectroscopic, the thermo-mechanical and the laser properties of the new old laser crystal Yb:CaF₂, of its Sr and Ba isotypes as well as of an Yb and Na codoped compound. It will be shown that Yb:CaF₂ is a very particular luminescent material, in which the laser-active center probably consists of a complex hexameric cluster, that it is the most promising Yb-doped fluoride material for large-scale, high-power and high-energy laser systems and that it can compete in several aspects with the currently used Yb-doped oxide crystals and glasses. The opportunity of operating the crystals at cryogenic temperatures and the recently achieved improvements in the field of femtosecond pulsed laser operation and high peak power laser amplification is highlighted and evaluated.