Optimization of a UV Cu+ laser excited bypulse-longitudinal Ne-CuBr discharge

The discharge conditions for high average output power on four UV Cu⁺ lines at 248.6 252.9, 260.0, and 270.3 nm, in a nanosecond pulse-longitudinal Ne-CuBr discharge, have been investigated in two discharge tubes of different designs. A record average output power of 210 mW (and a peak pulse power of 1.7 W) on the 238.6-nm laser line, and of 270 mW for multiline operation has been obtained. An optical effect enhancing the 248.6-nm laser line power has been observed as the intensity of two Cu atom laser lines (510.6 and 578.2 nm) increases. It has been shown that the presence of Br atoms in the discharge leads to a fall of the Ne metastable density via Penning ionization and, hence, to a decrease of the Cu⁺ metastable density and an increase of the laser output     

A copper HyBrID laser with 2 W/cm3 specific averageoutput power

A copper HyBrID laser (λ510.6, 578.2 nm) is reported, which produced an average output power of 9.5 W from an active volume of just 4.77 cm³. These figures correspond to a record specific average output power for copper lasers of any type of 2.0 W/cm³      

High average and high peak brightness slab laser

A high average and high peak brightness Nd:YAG MOPA laser system composed of a laser-diode-pumped Nd:YAG master oscillator, flash-lamp-pumped slab power amplifiers and a phase conjugated mirror was developed. The system demonstrates an average output power of 235 W at a repetition rate of 320 Hz and a peak power of 30 MW at a pulse duration of 24 ns with M²=1.5. Both an average brightness of 7×10⁹ W/cm²·sr and a peak brightness of 1×10¹⁵ W/cm2·sr are achieved simultaneously. The system design rules that we confirmed suggest that by replacing lamp pumping in the amplifier with laser-diode pumping, an average output power of ~1 kW can be obtained at ~1 kHz with a higher average brightness of ~3×10¹⁰ W/cm²·sr and a higher peak brightness of ~3×10¹⁵ W/cm²·sr     

Fast axial flow CO2 laser excited by silent discharge

A fast axial flow CO₂ laser excited by silent discharge has been developed. With a new electrode system applied to the laser, homogeneous discharge of power density of up to 80 W/cm³ is obtained without applying any stabilization techniques on the discharge. An output laser power of 920 W in stable TEM₀₀ mode operation is attained with an efficiency of over 14%. Beam fluctuation common to fast axial flow lasers is suppressed by the combination of smooth gas flow and low CO₂ molar fraction     

A CuBr laser with 1.4 W/cm3 average output power

An average laser power of 6.7 W has been obtained from a small-bore CuBr laser with a constructive active volume of 4.77 cm³ , i.e., a record specific average power of 1.4 W/cm³ for multikilohertz operation of copper vapor lasers has been achieved. It was found that the small-bore CuBr laser can operate with a neon buffer at atmospheric pressures     

Diode-pumped ytterbium-doped Sr5(PO4)3F laser performance

The performance of the first diode-pumped Yb³⁺-doped Sr ₅(PO₄)₃F (Yb:S-FAP) solid-state laser is discussed. An InGaAs diode array has been fabricated that has suitable specifications for pumping a 3×3×30 mm Yb:S-FAP rod. The saturation fluence for diode pumping was deduced to be 5.5 J/cm ² for the particular 2.8 kW peak power diode array utilized in our studies. This is 2.5× higher than the intrinsic 2.2 J/cm ² saturation fluence as is attributed to the 6.5 nm bandwidth of our diode pump array. The small signal gain is consistent with the previously measured emission cross section of 6.0×10^-20 cm², obtained from a narrowband-laser pumped gain experiment. Up to 1.7 J/cm³ of stored energy density was achieved in a 6×6×44 mm Yb:S-FAP amplifier rod. In a free running configuration, diode-pumped slope efficiencies up to 43% (laser output energy/absorbed pump energy) were observed with output energies up to ~0.5 J per 1 ms pulse. When the rod was mounted in a copper block for cooling, 13 W of average power was produced with power supply limited operation at 70 Hz with 500 μs pulses     

A discharge heated copper vapor laser

A simple, reliable copper vapor laser is described with vapor produced by discharge heating. Average output power of 1.3 W has resulted at 6.8 kHz and a specific energy of 39 μJ/cm³. Copper vapor density as high as3 times 10^{16}cm^-3was achieved.     

Measurements of intrinsic efficiency and parameters of an electronbeam pumped ArXe laser

Measurements of the output energy and intrinsic efficiency of an electron-beam-pumped ArXe laser operating on the 1.73-μm line are reported. A 220-kV electron beam was used to pump either an 11×11×50 cm³ or an 11×11×25 cm³ active volume. Small-signal gain, nonsaturable loss, and saturation flux were deduced from a Rigrod analysis of the output energies as a function of output coupler reflectivity. Electron beam pump powers ranging from 2.2 to 16.2 kW/cm³ were employed. At a pump power of 2.2 kW/cm³ a small signal of 0.035 cm^-1 , a gain-to-loss ratio of 272, and a saturation flux of 2.1 kW/cm ² were determined. Intrinsic efficiencies of 4% were obtained at the lower pump powers. From the measurements of the laser output it is clear that the secondary electrons have a significant impact on the laser kinetics and efficiency     

2-kHz repetition rate XeF laser

High-repetition-rate laser action, up to 2 kHz, has been demonstrated in XeF molecules at 351 and 353 nm by using a blowdown fast transverse-flow system and a four-circuit, thyratron-switched, low inductance pulse generator. For a typical run, the transverse flow was uniform, and the average flow velocity was 25 m/s across a discharge region of1.4 times 0.4 times 30cm³. The gas mixture used was He:Xe:NF3= 100:1.5:0.5, and the total pressure was varied from 600-1200 torr. For single-pulse operation, the maximum laser output energy was 22 mJ/pulse, and the electric efficiency was 0.4 percent. For a 2-kHz repetition rate, the average laser output energy was approximately 12 mJ/pulse with 50 percent variations. Hence, an average output power of 24 W was obtained.     

CW operation of monolithic arrays of surface-emitting folded-cavityInGaAs/AlGaAs diode lasers

A monolithic 0.84-cm² two-dimensional array of surface-emitting folded-cavity InGaAs/AlGaAs diode lasers was mounted junction up on a W/Cu microchannel heatsink and evaluated under continuous-wave (CW) operating conditions. Each laser in the array contained two upward-deflecting internal-cavity 45° mirrors which were etched using chlorine ion-beam-assisted etching, and two top-surface facets. The CW threshold current densities of different sections of the array were ⩽223 A/cm², while effective CW differential quantum efficiencies were ⩾30%. A CW output power of over 40 W was obtained from the entire array, while a current-limited output power density of 84 W/cm² with an average temperature rise of ~30°C was obtained from a quarter of the array     

CW radio-frequency excited white-light He-Cd+ laser

We report on the design and performance of a continuous-wave transverse capacitively coupled radio-frequency excited He-Cd⁺ laser, which is capable of simultaneously delivering stable, tens-milliwatt power output at the three primary spectral lines blue: (λ=441.6 nm), green (λ=533.7 nm and λ=537.8 nm), and red (λ=635.5 nm and λ=636.0 nm). Mixing these lines can result in the laser beam featured by a wide band of colors, including white color. The radio-frequency discharge, that excited the He-Cd mixture inside an alumina ceramic tube (400 mm length and 4 mm inner diameter) inserted into the fused silica tubing, operated between 400 mm long and 4 mm wide outer electrodes. Transformation of the radio-frequency discharge impedance to the 50-Ω output resistance of the radiofrequency generator and symmetrization of the radio-frequency voltage were performed by a special matching circuit. Under single-line operation the He-Cd⁺ laser output powers of 60 mW, 38 mW and 14 mW were obtained for the blue, green and red lines, respectively, at an input radio-frequency power of 400 W. Owing to the power interaction between the laser oscillations at red and green higher laser output powers in red and green are possible under multi-line operation. At optimum conditions the white-light laser output power of about 60 mW is obtainable from the laser tube of 40 cm active length. The rms noise-to-signal ratio (lower than 0.4%) of the laser output power of the radio-frequency excited He-Cd⁺ laser was comparable to that of hollow cathode He-Cd⁺ lasers and much lower than that of conventional positive column He-Cd⁺ lasers. The presented laser has exhibited stable operation for more than 400 hours, showing ability to become a long life laser     

Unsaturated gain and output power of a 6328 Å He-Ne gas laser

The population inversion between the3S_{2}level and the2P_{4}level for He-Ne gaseous laser is calculated by solving rate equations in the four-level system in the steady state. Using this result, the unsaturated gain and the output power in laser oscillation as a function of discharge current are obtained for laser mediums with inhomogeneously broadened lines. The output power dependency on the excitation parameter is also obtained. The collision width and various transition rates in the transfer from helium to neon, spontaneous emission, induced emission and absorption, electron collision, and diffusion are appropriately chosen for the mixture of 1.0 torr helium and 0.1 torr neon in a 6-mm ID laser tube. The theoretical values of single-pass unsaturated gain for 65-cm plasma length and output power are 4.7 percent and 38 mW/cm², respectively, for a discharge current of 30 mA. The experimental values are 4.5 percent and 33 mW/cm², respectively, and almost coincide with the theoretical values. Furthermore, the saturation parameter is obtained theoretically as 490 mW/cm².     

Repetitively pulsed transversely excited Sr+recombination laser

Operation of a transversely excited strontium-ion recombination laser at repetition rates up to 500 Hz is reported. Maximum average output power of 90 mW on the 430.5 nm transition has been obtained from a sealed-off device of active volume ∼ 40 cm³at a pulse repetition frequency of 200 Hz. This performace was achieved in the absence of any discharge preionization or forced recirculation of the gas mixture.     

High peak power and high repetition rate characteristics in acurrent-pulsed Q-switched CO2 laser with a mechanical shutter

An electro-mechanical Q-switched (EMQ) CO₂ laser is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current. Such a system can produce pulses with high peak powers (>10 kW) and high repetition rates (>1 kpps). In order to analyze the output characteristics, the peak power and the duration of the output pulses have been measured experimentally in detail over a wide range of Q-switching times up to 250 ns. For a low-pressure (<4 kPa) CO₂ gas system, the standard rate equations adequately explain the experimental results by introducing a new switching function for the form of the cavity loss for the mechanical chopper. In an EMQ-laser with a high initial inversion density (4.5·10¹⁵ /cm³ at 150 mA peak current), multiple peak pulses or pulse distortion have been observed. This is due to the plasma screening effect induced by the burning of the metal shutter blades placed inside the cavity. It is found that tungsten metal shutter blades can be used up to a power density of 259 MW/cm² for a focused beam without this effect occurring, The solutions of the rate equations show that optimum coupling can prevent the plasma screening effect even for a Q-switching time longer than the pulse buildup time. The EMQ-laser configured for optimum coupling has produced a peak output power of 30 kW for the 9P20 transition branch in the CO₂ spectrum without any pulse distortion. This value has been obtained even though the discharge length was only 1.3 meters     

Simultaneous emission of the HF and N2 lines from aplasma cathode TEA laser

Simultaneous laser action from HF and N₂ is obtained, from a plasma cathode TEA laser, for the first time. The sliding discharge along the surface of a dielectric is used as a plasma cathode, for the main volumetric discharge. The laser operates at atmospheric pressure, with a gas mixture of SF₆:C₃H₈:N₂:He. For a typical flow rate ratio of 0.27:0.024:0.2:19.8 1 min^-1, it produces simultaneously 160 mJ HF and 0.6 mJ N₂ laser outputs at 0.43% and 1.4×10^-3% efficiencies respectively, at the moderate charging voltage of 28.5 kV. These output characteristics are obtained from a small active discharge volume and length of 10⁶ cm³ and 38 cm respectively. These values extend the performance, recently reported in the literature, of a sliding discharge HF/N₂ laser with corresponding simultaneous energy outputs of 12 mJ HF and 1.1 mJ N₂, to a higher energy output level, thus making the device suitable for a broader range of applications. This novel dual wavelength HF/N₂ laser system presented, can be particularly convenient for medical experiments, where the IR beam can be used for tissue ablation, while the UV beam can be used as the excitation source for fluorescence spectroscopic measurements, for the evaluation of the ablation process. Details are presented on the dependence of the laser performance parameters, such as output energy, discharge voltage and current and structure of the laser output pulses on the mixture composition and the circuit parameters     

GaInNAs-GaAs long-wavelength vertical-cavity surface-emitting laserdiodes

Vertical-cavity surface-emitting laser diodes with GaInNAs-GaAs quantum-well (QW) active layers are demonstrated for the first time. GaInNAs permits the realization of a long-wavelength vertical-cavity laser grown directly on a GaAs substrate. Room-temperature (RT) pulsed operation is achieved, with an active wavelength near 1.18 μm, threshold current density of 3.1 kA/cm², slope efficiency of ~0.04 W/A, and output power above 5 mW for 45-μm-diameter devices. Laser oscillation is observed for temperatures at high as 95°C     

High-power, tunable, high-repetition rate TEA-13C18O2 laser

The authors report the power enhancement of a high-repetition-rate TEA-¹³C¹⁸O₂ laser by substitution of rare ¹⁵N₂ isotope instead of ¹⁴N₂ and its tunable single-mode operation. Efficient, high-power operation with a maximum average power of 25 W (100 Hz) at a slope efficiency of 5.6%, which is improved by a factor of 2 by substitution of ¹⁵N₂ instead of ¹⁴N₂, has been successfully achieved from a discharge volume of 57.5 cm³ with an active length of 26 cm. In addition, high-power, tunable, single-mode operation has been achieved with a three-mirror cavity consisting of two mirrors and a Littrow grating     

20 W CW surface emitting 0.8 μm GaAs/GaAlAs laser diodes

A continuous-wave optical power density of 200 W/cm² is reported for the first time for a 0.1 cm² element of a surface emitting GaAs/GaAlAs wafer. The laser facets are cleaved on-wafer by a microcleavage technique. The output optical beam is reflected by 45°-integrated beam deflectors situated at a distance of 15 μm from each laser facet. The lasers were soldered junction-up on a microchannel CuW cooler. The drive current at 20 W CW is 40 A with a slope efficiency of 0.7 W/A     

Effects of near-infrared laser and superluminous diode irradiationon Escherichia coli division rate

An investigation is conducted of the effect of a 1300-nm continuous-wave (CW) laser diode 950-nm modulated superluminous diode which had a fixed average power density of 1.2×10³ W/m ² at all variable repetition rates of 2, 26, 700, 1000, and 5000 Hz and had an equivalent pulse duration of 410, 31.1, 1.15, 0.82, and 0.16 ms, respectively. The effect of both diodes on the rate of Escherichia coli WP2 division was examined. It was found that the radiation of the CW mode of the 1300-nm laser diode increased the division of E. coli in the dose range of 0.9-9.0 J/cm². The 950-nm pulsed irradiation increased or inhibited the division rate of bacteria depending on the pulsing frequency and/or pulse duration     

Simultaneous Q-switching and mode-locking in a diode-pumped Nd:YVO4-Cr4+:YAG laser

Parametric studies of passive Q-switching and mode-locking in a Nd ³⁺:YVO₄-Cr⁴⁺:YAG laser were theoretically carried out. Simultaneous mode-locking and Q-switching was also experimentally studied. It was found that over 90% of the output power could be mode-locked in a diode-pumped passively Q-switched Nd³⁺:YVO₄-Cr⁴⁺:YAG laser. The average pulse duration of the mode-locked pulse train was estimated to he around 110~150 ps. The highest peak power of a single pulse near the maximum of the Q-switched envelope was greater than 100 kW