Characteristics of the high-pressure Ar-Xe laser pumped by anelectron beam and an electron-beam sustained discharge

Mechanisms of the line competition observed among the 1.73-, 2.03-, and 2.65-μm lines are interpreted based on the gain and saturation data along with some known kinetics. The energy distribution among the lines is also investigated as a function of various operating parameters. An enhancement factor of ~10 was readily obtained for both electrical input energy and laser output energy in the e-beam sustained discharged. However, there is a tradeoff between enhancement factors and laser output energy due to a degradation of the laser output observed for discharge power enhancements greater than 5. The maximum output energy obtained was 4 J/l, with an intrinsic efficiency of ~3%     

Impact of electron collision mixing on the delay times of anelectron beam excited atomic xenon laser

The atomic xenon (5d→6p) infrared laser has been experimentally and theoretically investigated using a short-pulse (30-ns), high-power (1-10-MW/cm³) coaxial electron beam excitation source. In most cases, laser oscillation is not observed during the e-beam current pulse. Laser pulses of hundreds of nanoseconds duration are subsequently obtained, however, with oscillation beginning 60-800 ns after the current pulse terminates. Results from a computer model for the xenon laser reproduce the experimental values and show that oscillation begins when the fractional electron density decays below a critical value of ≈0.2-0.8×10 ⁶. These results lend credence to the proposal that electron collision mixing of the laser levels limits the maximum value of specific power deposition that can be used to excite the atomic xenon laser efficiently on a quasi-CW basis     

Kinetic processes in electron beam-excited XeF (C40aA) laser media

Fundamental processes affecting the operation and performance of electron beam-excited XeF(C→A) laser media have been analyzed and modeled. Emphasis has been placed on conditions typical of high current density (~250A cm^-2), short pulse (~10 ns FWHM) e-beam excitation of high pressure (~6 atm) multicomponent mixtures comprised of Ar-Kr-Xe-NF₃-F₂ . Computation of the temporal evolution of excited and ionized species for such circumstances has permitted identification of the factors controlling XeF(C) formation and loss, and has resulted in the identification of the primary transient species that absorb radiation in the blue-green spectral region. The data so obtained serve to explain measured XeF(C→A) properties, particularly net gain, under conditions for which the C→ A laser energy density and efficiency values are comparable to those of the UV XeF(B→X) laser     

Gas temperature dependent output of the atomic argon and xenonlasers

Laser power and energy have been measured for the transitions at 1.73 and 2.03 μm in atomic xenon, and 1.27 and 1.79 μm in atomic argon, for gas temperatures between 290-585 K. Nuclear excitation using ²³⁵U fission-fragments provided pump powers between 2-10 W/cm ³. Peak laser output in xenon was independent of gas temperature below 400 K. Laser output at 1.79 μm in argon decreased monotonically with increasing gas temperature while the 1.27 μm laser output was independent of gas temperature below 380 K. In all cases, the laser threshold increased as the gas temperature increased     

Direct bandwidth and polarization control of an XeF unstableresonator laser

Several approaches to directly controlling the bandwidth and polarization of an unstable resonator without the use of an injection source are discussed. The techniques are based on the control of oscillations within (and around) the resonator core through the use of small, subaperture optical elements (e.g. etalons, Brewster-angle plates, Glan-air prisms) mounted at select locations within the system. The experiments were performed on a 4-J, e-beam pumped, XeF ( B→X) laser operating at ambient temperature, with output predominantly at 353.2 nm. A spectral linewidth of less than 12 GHz (0.05 Å) and nearly perfect linear polarization were simultaneously achieved at high laser efficiency. Oscillation on a single, dominant transverse mode has been demonstrated. The increased cost and complexity of injection-controlled systems are avoided through the use of these direct, core-control approaches     

Time-resolved spectroscopic study of high-pressure self-sustaineddischarge-pumped atomic xenon lasers

To explore the lasing kinetics of UV-preionized, self-sustained discharge-pumped atomic xenon (5d→6p) lasers, the time-resolved spectroscopy of the laser output from the multiline laser resonator is reported. The dilutents used were Ar and He. Increasing Xe concentration shortened the 1.73-μm laser pulse duration and decreased the total (multiline) laser output energy, because increased Xe metastable state population contributes to the increase of the 6p state population (lower laser level) by electron-impact excitation and radiation trapping during discharge pumping. High-excitation-rate pumping resulted in the decrease of the laser output power of 1.73- and 2.63-μm lines. Increasing the total gas pressure leads to high-efficiency operation due to modest-excitation-rate pumping at high pressures     

High-pressure infrared xenon laser with X-ray preionization

The first experimental results are presented of an X-ray preionized argon-buffered xenon laser. The X-rays are generated by a simple electron-beam device located below the 23-cm inner diameter laser chamber. The advantages of X-ray preionization for high-pressure discharge-pumped lasers include the long X-ray penetration depth, high preionization density, and spatial uniformity. The combination of X-ray preionization and techniques to eliminate surface flashover allows energetic operation in 4 atm of argon buffer for the first time in a photopreionized discharge laser. The argon-xenon mixtures lased primarily at 1.73 μm and 2.63 μm with a peak energy of 340 mJ at 4 atm, and a specific energy output of 0.85 J/liter     

Return current in large aperture electron-beam-excited KrF lasers

Results from a model for an e-beam excited KrF laser are presented, and the effects of return currents on plasma parameters and laser performance are discussed. The author finds that the joule heating caused by the return currents, expressed as a fraction of total power deposition, increases with increasing halogen density, increasing aperture size, increasing pressure, and decreasing power deposition. The return current electric field causes a decrease in the rate coefficients for dissociate recombination and attachment and an increase in the rate of multistep ionization. As a result, the electron density near the foil increases by more than tens of percentage points. The laser intensity in those regions also increases. These effects are practically important in lasers having apertures exceeding 1 m     

The optimization of the multi-atmospheric Ar-Xe laser

The quasi-steady-state conditions of the multi-atmospheric e-beam sustained Ar-Xe laser are investigated. It is observed that the duration of the stationary period depends on the e-beam current, discharge power deposition, and gas pressure. The laser efficiency can be as high as 8%. Beyond the stationary period the efficiency drops. The pulse energy with optimum efficiency depends strongly on the gas pressure. The maximum discharge efficiency of 5%-6% is at high pressure not sensitive to the input power. The best results are obtained for 4 bar with a discharge input power of 8 MW/l. The pulse duration with corresponding output energies is 12 μs with 10 J/l and 16 μs with 16 J/l for e-beam currents of 0.4 and 0.9 A/cm², respectively. An analysis of the quasi-steady-state conditions that include the effects of electron collision mixing and atomic quenching is presented. The effects of output power saturation by the fractional ionization and atomic collisions are in agreement with the observations. The analysis clarifies the optimum performance conditions     

An EMQ-switched CO2 laser as a pump source for afar-infrared laser with a high peak power and a high repetitionrate

A modified current pulsed Q (EMQ)-switched CO₂ laser which is Q-switched by a mechanical beam chopper in combination with a pulsed discharge current is discussed. The laser produces a very stable output with a peak power greater than 1 kW at a repetition rate of 1000 p.p.s. for all transitions in the P and R branches of the CO₂ spectrum. A CH₃F laser pumped by the EMQ-switched laser produces 496 μm radiation in a 6.5 W peak, 100 ns pulses at 500 p.p.s. in the lowest loss EH₁₁ mode     

Three-dimensional analysis of an FEL amplifier operating with acontinuous e beam

The authors discuss a three-dimensional theory of an FEL operating with a continuous e beam. The theory is based on a generalized method of solution of the FEL Helmholtz equation in the high-gain small-signal regime. The method consists basically of expanding the optical field in terms of Hermite-Gaussian modes, taken at the entrance to the undulator. The coefficients of that expansion are expressed in the form of a superposition of plane waves with complex frequencies. As a result, one gets a set of recursive relations, partly reproducing those obtained within the context of the single-mode evolution and partly displaying the effect (revealed by a coupling among the modes) of both the diffraction and the interaction with the e-beam     

Acoustooptic Q-switching of erbium lasers

Experiments were performed on Q switching of erbium lasers at 3 μm with an acoustooptical modulator. Different laser crystals of YAG:Er and YSGG:Cr:Er have been investigated. The highest fraction of single pulse Q-switch energy to free-running mode energy was 1%. Pulse durations of 50 ns were obtained. Multiple switching with up to 14 Q-switch peaks per flashlamp pulse could be generated, containing up to 19% of the energy of the free-running mode     

Germanium-diffused waveguides in silicon for λ=1.3 μm andλ=1.55 μm with losses below 0.5 dB/cm

The authors present a simple technique for the fabrication of integrated optical channel waveguides that are prepared by indiffusion of an E-beam evaporated amorphous alloy of germanium and silicon into commercially available silicon with low dopant concentration, using only simple technological processes such as standard lithography, PVD, and diffusion. The waveguides are polarization independent and have waveguide losses as low as 0.3 dB/cm at wavelengths of λ=1.3 μm and λ=1.55 μm. The spot sizes are well suited for low-loss single-mode fiber device coupling, being on the order of a few microns in both horizontal and vertical directions     

Injection control of a multipass amplification of a dischargeexcited XeF (C→A) laser

The laser performance and kinetic properties of the broadband C→A transition of the XeF*-exciplex have been studied under discharge excitation. With a pulsed dye laser as the injection source, amplified output pulses with an energy of up to 4 mJ have been obtained in the wavelength range from 450 to 520 nm. Injection of a well-defined seed pulse in an unstable confocal cavity has been developed into a useful technique for identification of subtle kinetic details of the complicated lasing process in XeF*, such as the role of the competitive narrow-band B→X transition or the influence of the various buffer gases     

Frequency-locking of a 1.3 μm DFB laser using a miniature argonglow lamp

The frequency of an InGaAsP distributed-feedback (DFB) laser was locked to the 2p₁₀-3d₅ transition of argon atoms at 1.2960 μm using the optogalvanic signal obtained from a commercial miniature glow lamp. At a discharge current of 500 μA, the signal-to-noise ratio of the optogalvanic signal corresponding to the Ar transition was about 18 dB. The peak-to-peak width of the first derivative signal was 650 MHz. The slope of the signal was 0.32 μV/MHz near the center of the transition. By using the linear portion of the first-derivative signal, the laser frequency was locked to the Ar 2p₁₀-3d₅ transition. The peak-to-peak frequency fluctuations in the free-running condition were estimated to be 650 MHz, which is mainly due to laser temperature fluctuations. When the servo-loop was closed, the frequency stability was improved to better than 13 MHz     

A single frequency Nd:YAG ring laser pumped by laser diodes

The design and operation of a diode-pumped Nd:YAG ring laser is described. The laser is shown to be a highly versatile device, capable of efficient generation of both the fundamental and second harmonic frequencies, CW and Q-switched. Single-frequency outputs in excess of 540 mW at 1.06 μm and 18.9 mW at 532 nm output were obtained, whereas multi-longitudinal mode Q-switched operation produced 22.4 μJ per pulse at 5 kHz in the fundamental and 7.3 μJ power pulse at 532 nm     

High vibrational temperatures in optically-pumped CO2

A pulsed 4.3-μm CO₂ laser was used to optically pump mixtures of CO₂ and He, and create transient gain at 9 and 10 μm. A conventional continuous-wave CO₂ laser operating on both regular and sequence bands measures this transient gain, and determined the ν₃ (asymmetric stretching)-mode vibrational temperature T₃. The measured values of T ₃ are generally much higher than those attained in discharge-excited CO₂. It is shown that a Treanor distribution must be used to describe the populations in the ν₃ -mode when dilute mixtures of CO₂ in He are optically pumped to ν₃-mode temperatures of 3000 to 4000 K. Under these conditions the sequence-band gain coefficients are almost equal to those on the regular bands. The collisional relaxation of energy from the ν₃ mode shows evidence of fast V-T relaxation at high values of T₃, followed by a slower relaxation rate characteristic of the 00⁰1 population lifetime     

Energy loading effects in the scaling of atomic xenon lasers

The intrinsic power efficiency of the atomic xenon (5d→6p) infrared (1.73-3.65-μm) laser is sensitive to the rate of pumping due to electron collision mixing of the laser levels. Long-duration pumping at moderate power deposition may therefore result in higher energy efficiencies than pumping at higher powers. The consequences of high energy deposition (hundreds of joules per atmosphere) during long pumping pulses (hundreds of microseconds) on the intrinsic power and energy efficiency and optimum power deposition of the atomic xenon laser are examined. The dominant effect of high energy loading, gas heating, causes an increase in the electron collision mixing of the laser levels. The optimum power deposition for a given gas density therefore shifts to lower values with increasing gas temperature     

Distributed feedback laser diode and module for CATV systems

Harmonic distortion of distributed feedback laser diodes (DFB-LDs) for analog transmission systems is investigated. It is shown that, under a modulation frequency of less than 1 GHz, the harmonic distortion depends on the nonlinearity of the light output power-current (P-I) curve under the continuous wave (CW) condition, which is determined by the coupling constant κ L, and that the distortion can be minimized at κ L~1. A 1.3 μm wavelength InGaAsP DFB-PPIBH (p-substrate partially inverted buried heterostructure) LD and its module, with low distortion by the control of a coupling constant, have been developed     

Submilliamp threshold InGaAs-GaAs strained layer quantum-well laser

Strained-layer InGaAs-GaAs single-quantum-well buried-heterostructure lasers were fabricated by a hybrid beam epitaxy and liquid-phase epitaxy technique. Very low threshold currents, 2.4 mA for an uncoated laser (L=425 μm) and 0.75 mA for a coated laser (R~0.9, L=198 μm), were obtained. A 3-dB modulation bandwidth of 7.6 GHz was demonstrated at low bias current (14 mA). Procedures for material preparation and device fabrication are introduced