A DC excited waveguide multibeam CO2 laser using high frequency pre-ionization technique

High power industrial multibeam CO₂ lasers consist of a large number of closely packed parallel glass discharge tubes sharing a common plane parallel resonator. Every discharge tube forms an independent resonator. When discharge tubes of smaller diameter are used and the Fresnel numberN ≪ 1 for all resonators, they operate in waveguide mode. Waveguide modes have excellent discrimination of higher order modes. A DC excited waveguide multibeam CO₂ laser is reported having six glass discharge tubes. Simultaneous excitation of DC discharge in all sections is achieved by producing pre-ionization using an auxiliary high frequency pulsed discharge along with its other advantages. Maximum 170 W output power is obtained with all beams operating in EH₁₁ waveguide mode. The specific power of 28 W/m is much higher as compared to similar AC excited waveguide multibeam CO₂ lasers. Theoretical analysis shows that all resonators of this laser will support only EH₁₁ mode. This laser is successfully used for woodcutting     

Improvement of the performance of cw CO lasers by using externally ribbed wall cooled discharge tubes

 We describe a modified design of a continuous-flow cw CO laser with longitudinal electric discharge using an externally ribbed wall cooled discharge tube. The transverse ribbed discharge tube provides a more intense heat exchange of the CO-laser gas with the walls. With this configuration it was possible to obtain about 50% more output power from an all-line CO Δv=1 laser. For a CO-overtone Δv=2 laser we were able to improve both the output power and the number of lines as compared to a conventional smooth tube. Received: 23 April 1996     

Characteristics of a flowing He-SrCl2 vapor laser

An experimental investigation on the characteristics of a flowing He-SrCl₂ vapor laser is carried out. The output power as a function of the SrCl₂ vapor pressure is presented by calculating the radial temperature distribution of the discharge tube. The temporal dependences of the discharge current pulse on the laser pulses at 1 μm, ∼ 3 μm and 6.45 μm lines in strontium atom and ion, as well as the spot modes of the laser beam are measured and analyzed under different laser output power.     

Nd:YAG waveguide laser with 1.3 W output power, fabricated by direct femtosecond laser writing

Tracks of modified material were written with femtosecond-laser pulses in neodymium-doped YAG crystals. Due to a stress-induced change of the refractive index, waveguiding beside the tracks and between two adjacent tracks with a distance of approximately 25 μm was observed. Loss measurements resulted in guiding losses of about 1.6 dB/cm for the double track waveguide. Spectroscopic investigations of the ⁴ F _3/2→⁴ F _11/2 transmission lines of the neodymium ions, which are close to the modified region, revealed a small stress-induced red shift of the lines. Laser oscillation of single-track waveguides and double-track waveguides was demonstrated with Ti:Sapphire laser pumping at a wavelength of 808 nm. Best laser performance with about 1.3 W output power at 2.25 W launched pump power was achieved using a double-track waveguide with a separation of 27 μm at an outcoupling transmission of 95%.     

电泳式He-Sr+复合激光特性研究

设计制作了7mm内径和38cm有效激励长度的电泳式He-Sr⁺激光管,采用修饰Blumlein电路,通过纵向高重复率脉冲放电激励,实现了一价锶离子复合激光430.5nm和R-M跃迁激光1.03μm的同时振荡,其中复合激光占主要成分.测量分析了复合激光输出功率与工作参量(脉冲频率,充电电源电压和氦压)的关系曲线.获得了最大激光功率819mW和56mW/cm³功率密度的实验结果. 关键词： 锶离子激光 电泳 脉冲放电     

High power operation of a CW 28 μm water vapor laser

This paper describes the best operating conditions and power performance of a CW 28 μm water vapor laser, using a 3 m long discharge in a 3 cm diameter Pyrex glass tube. The laser cavity is a half symmetric conventional Fabry-Perot resonator, the plane mirror of which is a metal mesh used as an output coupler. The addition of a large amount of hydrogen to the water vapor leads to the production of high power laser emission. This laser delivers 230 mW of continuous output at 28 μm, corresponding to a volumetric power of 102 μW/cm³, the highest value ever reported.     

Measurement of electric field strengths in a waveguide by means of the dynamic Stark effect in hydrogen and neutral helium spectral lines

The dynamic Stark effect of the spectral lines H_β and of the neutral helium lines λ=402.6 nm (2³ P ⁰−5³ D) and λ=438.8 nm (2¹ P ⁰−5¹ D) emitted from a discharge tube was used for probing rf electric fields in a transverse waveguide. Calculations accounting for the pertubation of the atomic states by strong unidirectional fields prove to be suitable in order to interprete the main experimental results. If the waveguide is terminated with a metallic reflector and the plasma in the discharge tube becomes overdense—then representing a slightly permeable mirror—a resonant enhancement of the electric field strength may be achieved by tuning. This enhancement is well recognizable in the spectral line contours.     

Output characteristics of a cataphoresis He–Sr recombination laser

A cataphoresis discharge tube of 7 mm inner diameter and 38 cm active length was designed and made for the He–Sr⁺ laser. The cataphoretic input of uniform distribution of strontium vapor concentrations along the active region was realized by the cataphoresis effect and the slow flowing (0.5 nl/h) of helium buffer gas. The strontium ionic recombination laser at 430.5 nm and the R–M transition laser at 1.03 μm were obtained with the modified Blumlein circuit by high-frequency longitudinal pulsed discharge. The laser components are concentrated on the 430.5 nm wavelength. Dependences of working parameters such as the pulse frequency, the supply voltage, and the helium pressure on laser output characteristics were measured and discussed. The maximum laser output power of 819 mW and specific power of 56 mW/cm³ were obtained, respectively.     

Microwave energy channeling in plasma waveguides created by a high-power UV laser in the atmosphere

The grazing mode of microwave propagation in a hollow plasma waveguide formed by ionization of atmospheric air with a small easily ionized additive by strong UV pulses of the Garpun KrF laser (λ = 248 nm, the pulse duration and energy are ∼70 ns and ∼50 J) was experimentally demonstrated for the first time. The annular laser beam produced a hollow tube ∼10 cm in diameter with an electron density of ∼10¹² cm⁻³ in a plasma wall ∼1 cm thick, over whichmicrowave radiation with λ _mw ∼ 8 mm was transmitted to a distance of 60 m. Themicrowave signal transmitted by the waveguide was amplified by a factor of 6 in comparison with propagation in free space.     

Simultaneous dual-wavelength emission at 0.90 and 1.06 µm in Nd-doped laser crystals

Continuous-wave (CW) simultaneous laser emission on the 0.9-μm ⁴ F _3/2 → ⁴ I _9/2 transition and the ⁴ F _3/2 → ⁴ I _11/2 transition at 1.06 μm is obtained in Nd-based laser crystals of thin-disk geometry and using a multi-pass pumping scheme. A Nd:Y₃Al₅O₁₂ (Nd:YAG) thin disk emitted simultaneous laser radiation at 946 and 1064 nm with 5.1 W output power, and Nd:YVO₄ and Nd:GdVO₄ thin-disk lasers with more than 3 W output power at 0.91 and 1.06 μm were realized. The ratio between the output power at one of the wavelengths and the total output power could be varied by the laser resonator design. An intracavity frequency-doubled Nd:YVO₄ thin-disk laser with alternate green at 532 nm and “deep-blue” at 457 nm generation of high average output powers is demonstrated.     

Power and radiance scaling of a 946 nm Nd:YAG planar waveguide laser

We present a diode-end-pumped Nd:YAG planar waveguide laser operating on neodymium’s quasi-four-level transition at a wavelength of 946 nm. Two modes of operation are described: a high-power multi-mode monolithic cavity generating 105 for 210 W of incident pump power with a slope efficiency of ∼54%, and secondly, a high-radiance configuration employing an external stable resonator producing a maximum output power of 29.2 for 86.5 W of incident pump-power, with a slope efficiency of 33%. The output beam quality values of the external cavity were M² of 3.2 by 2.4, leading to a maximum radiance of 0.43 GW cm⁻² sr⁻¹.     

High-performance,continuous-wave quantum-cascade lasers operating up to 85°C at <Emphasis Type="Italic">λ</Emphasis>∼8.8 μm

High-temperature, high-power, and continuous-wave (CW) operation of quantum-cascade lasers with 35 active/injector stages at λ∼8.85 μm above room temperature is achieved without using a buried heterostructure. At this long wavelength, the use of a wider ridge waveguide in an epilayer-down bonding scheme leads to a superior performance of the laser. For a high-reflectivity-coated 21 μm×3 mm laser, the output power of 237 mW and the threshold current density of 1.44 kA/cm² at 298 K under CW mode are obtained with a maximum wall-plug efficiency of 1.7%. Further improvements were observed by using a 4-mm-long cavity. The device exhibits 294 mW of output power at 298 K and it operates at a high temperature, even up to 358 K (85°C). The full widths at half-maximum of the laser beam in CW operation for the parallel and the perpendicular far-field patterns are 25°and 63°, respectively.     

Modelling of a simple Dy<Superscript>3+</Superscript> doped chalcogenide glass fibre laser for mid-infrared light generation

A simple Dy³⁺-doped chalcogenide glass fibre laser design for mid-infrared light generation is studied using a one dimensional rate equation model. The fibre laser design employs the concept of cascade lasing. The results obtained demonstrate that efficient cascade lasing may be achieved in practice without the need for fibre grating fabrication, as a sufficient level of feedback for laser action is provided by Fresnel light reflection at chalcogenide glass fibre–air interfaces. Further enhancement of the laser efficiency can be achieved by terminating one of the fibre ends with a mirror. A numerical analysis of the effect of the Dy³⁺ doping concentration and fibre loss on the laser operation shows that with 5 W of pump power, at 1.71 μm wavelength, output powers above 100 mW at ∼ 4.5 μm wavelength can be achieved with Dy³⁺ ion concentrations as low as 3 × 10¹⁹ cm⁻³, when fibre loss is of the order 1dB/m.     

A CW DCN waveguide laser of high volumetric efficiency

This paper describes a CW submillimeter waveguide laser operating on 190 and 195 μm DCN lines with high volumetric efficiency. The laser cavity is a 3.2 cm inner diameter, 70 cm long, Pyrex tube with plane reflectors (one of them is a copper mesh) against its ends. After optimization of various parameters (such as the N₂:CD₄:He gas mixture, the pressure and the discharge current, the wall temperature and the output coupling), this laser, with only 57 cm long active discharge, delivers 8.4 and 7.6 mW on the 190 and 195 μm lines, respectively, for the EH₁₁ mode. This represents volumetric powers of 75 and 65 μW cm^-3. The free space propagation of the EH₁₁ fundamental mode was found to be as for a gaussian beam, and the absorption of the laser beam in the atmosphere was also measured.     

Spectroscopy and cw operation of a 1.85 μm Tm:KY3F10 laser

Room-temperature cw laser operation on the ³ F ₄?³ H ₆ transition at 1.85 μm of Tm³⁺ ions in a KY₃F₁₀ single crystal is reported here for the first time. Using a cw Ti:sapphire laser as a pump source, a threshold absorbed pump power of 120 mW and a laser slope efficiency of 42.5% were achieved by using a 45% transmissive output coupler. Optimization of the activator concentration and crystal length is discussed taking into account self-quenching and pump-absorption efficiencies as well as parasitic and intrinsic reabsorption losses. The emission cross-section at the laser wavelength is determined using different methods, showing that the result of the J–O approach is, in this case, very uncertain. Received: 2 January 2001 / Revised version: 7 February 2001 / Published online: 27 April 2001     

Waveguide CO2 lasers on sequence-band transitions

Two waveguide CO₂ lasers, a quartz waveguide and an alumina waveguide, have been studied on the 00°2–[10°l,02°1]_I,II sequence bands. The use of an intra-cavity hot CO₂ cell, which is a part of the waveguide, suppresses the regular-band transitions. The quartz waveguide laser has a total of 58 lines lasing on both the 9.4 µm and 10.4 µ,m sequence bands. The alumina waveguide laser has 36 lines lasing on the 10.4 µm sequence band and twice the output power of the quartz waveguide laser, whereas lasing on the 9.4 µm sequence band is difficult. The lasers can be operated on the selected single line without line jumping problem. The frequency tuning range of the strong lines is limited by the free spectral range of the cavity.     

CO<Subscript>2</Subscript> laser oscillating in the range of 16 μm

The ability of a CO₂ laser to oscillate in the range of 16 (14) μm at room temperature was investigated experimentally and theoretically. The output energy per pulse was ~60 mJ at peak power of ~50 kW. It was necessary to minimize not only harmful losses but also useful ones in both channels 00⁰1–02⁰0 and 02⁰0–0110 and to increase the input energy, i.e., the density of free electrons in the discharge, in order to increase the peak power and energy of 16-μm radiation. The highest values of peak power and energy of radiation were reached at different pressures of the active mixture. The rotational bottleneck effect limiting the peak power and energy of oscillation was important at rather low pressures of the active medium. Oscillation at the R12 line is more preferable than that at the P12 line for use as 9.6-μm dumping radiation.     

Pulsed barium vapor laser with hydrogen additive and interactive circuit

A small-size discharge heated barium vapor laser with an axial temperature controller was designed and made. The operational characteristics of the laser with different hydrogen additives and two excitation circuits were experimentally investigated and compared. The results indicate that the addition of a small ratio (1.5%) of hydrogen to neon and the interactive circuit (IC) can greatly increase the laser output power. The maximum average laser power of 3.5 watts and a record specific power of 117.3 mW/cm³ at a 1.5 μm wavelength were obtained under optimal discharge conditions. Some possible mechanisms were suggested to explain the enhanced effect of the hydrogen additive and IC to the laser output performances. PACS 42.55.Lt; 42.60.Lh; 52.80.Tn     

CW efficient optically-pumped far-infrared waveguide NH3 lasers

Significant improvements in both output power and threshold pump power have been obtained by using a small-bore (6- and 12-mm ID) copper waveguide cavity in a CW optically pumped FIR NH₃ laser. Conversion efficiencies of 10–20% the theoretical maximum and volumetric photon-conversion efficiencies 0.1–0.2%/cm³ are obtained for the 81.5-μm line, and threshold pump powers as low as 0.03 W at 81.5 μm and 0.06 W at 263.4 μm are reported. It is shown that both the output and the threshold can be improved by employing a longer waveguide cavity in the 5–160 cm length range. Lasing in a compact waveguide NH₃ lasers is also demonstrated.