Copper-vapor laser with closed-cycle tranverse vapor flow

Fast closed-cycle transverse flow can be achieved in metal-vapor lasers by means of an evaporation-condensation cycle, with gravity return of the condensate. A small double-pulsed copper-vapor laser utilizing this technique operates at rates in excess of5 times 10^{4}pps.     

Performances of a frequency offset locked He-Xe laser system at 3.51 µm

A highly stabilized frequency offset locked He-Xe laser system was constructed for high resolution laser spectroscopy of H2CO [5_{1,5}(upsilon = 0) rightarrow 6_{0,6}(upsilon_{5}= 1)] at 3.51μm. It is composed of three He-Xe lasers. The first laser is H2CO-stabilized and is used as a frequency reference in the system. The second laser is frequency offset locked to the first laser by using the beat frequency between these lasers, and is used as a local oscillator. The third laser is frequency offset locked to the second laser, and is used to observe the H2CO spectrum by slowly varying the beat frequency between these lasers. The frequency stability of the first laser, measured against a similarly stabilized and synchronously modulated laser, was1.0times10^{-14}attau = 100s, where τ represents the integration time. The frequency traceability of the second laser to the first laser was expressed as8.0times10^{-13} cdot tau^{-1}for 10 msleq tau leq 100s. It was found that this value of the traceability was independent of the frequency modulation of the first and second lasers. The frequency traceability of the third laser to the second laser was nearly equal to that of the second laser described previously. The variable range of the frequency of the third laser was 19 MHz. In this range, the frequency traceability of the third laser to the second laser was independent of the beat frequency between these two lasers. From these results, it was concluded that this system can be used for the observation of the H2CO spectrum.     

Discharge lasers pumped by generators with inductive energy storage

Generators with inductive energy storage units and semiconductor opening switches designed for laser excitation are described. Operation of the generators on a gas-discharge load is considered and possible excitation modes are discussed. A longitudinal N₂ laser, transverse discharge nonchain HF laser, and CO₂ laser are developed based on this pumping technique. Output energies of 0.6 J and 3.2 J and laser efficiencies of 5.5% and over 17% were demonstrated on H ₂-SF₆ and He-CO₂-N₂ gas mixtures, respectively. High laser parameters obtained demonstrate the considerable promise of such inductive generators for pumping different gas lasers     

Optical and RF characteristics of short-cavity-lengthmultiquantum-well strained-layer lasers

The optical and RF characteristics of short-cavity, strained-layer In_0.3Ga_0.7As graded-index separate-confinement-heterostructure (GRINSCH) multiple-quantum-well ridge waveguide lasers are described. Short-cavity-length strained-layer lasers with four In_0.3Ga_0.7As quantum wells have been fabricated using chemically assisted ion beam etching (CAIBE). These lasers have a very low K factor of 0.14 ns and a high differential gain of 1.1×10^-15 cm². A 3 dB modulation bandwidth of 23.5 GHz has been measured on a 50 μm cavity-length device. This is the highest reported bandwidth for a quantum well laser     

Stabilized efficient single-frequency Nd:YAG laser

It is shown how intracavity etalons can be optimally designed for axial mode selection and frequency stabilization of gas and crystal lasers. Relevant laser parameters, required etalon properties, and expected losses are determined. A simple frequency stabilization scheme based on birefringent etalons is described, which does not require laser modulation. Major problems associated with stable single-frequency operation of solid-state lasers are discussed. Using an optimally designed crystal quartz etalon, a Nd:YAG laser could be stabilized to 10^-7in frequency and 2 percent in amplitude. The linearly polarized single frequency TEM00output was 150 mW, which compares to an unpolarized 12-mode output of 400 mW for the bare laser.     

Plasma chemistry of the closed-cycle 1 kHz transversely excitedatmospheric CO2 laser with an efficient catalytic CO2 regenerator

A high-power closed-cycle 1 kHz transversely excited atmospheric (TEA) CO₂ laser with an efficient catalytic CO₂ regenerator was used to investigate the variations of the average laser output power and the concentrations of the CO₂, CO, and O₂ molecules in the laser gas mixture with the operational performance of the CO₂ regenerator. It was experimentally shown that for the laser gas mixture of CO₂-N₂-He=15-15-70% and the output coupler reflectivity of 70%, η of 0.1 was required to maintain the laser output power greater than 90% of the initial laser output power of 570 W at an input energy density and a clearing ratio of 150 J/L and 3.0, respectively     

A stacked Blumlein N2laser

A novel device for producing fast-rise-time, large-volume electrical-discharge excitation of gas lasers is described. Some operating characteristics of an N2ultraviolet (UV) laser are presented.     

Improved performance of an electrically initiated HF laser

Some methods for improving the efficiency of electrically initiated HF lasers are discussed. Measurement of the laser pulse shape produced by 30-ns discharges in SF6:C2H6at several mixtures and pressures is reported. These pulse shapes are compared to the laser and current pulses produced by a two-stage Marx bank that gives laser pulses of 1.4 J with 3.1-percent electrical efficiency from an active volume of 0.331. A second bank is described, which gives pulses up to 3.5 J with 1.8-percent efficiency, with a peak power of 35 MW.     

Monolithic multiple wavelength surface emitting laser arrays

A two-dimensional (2-D) surface emitting laser array emitting 140 unique, nonredundant, uniformly separated, single-mode wavelengths in the 980-nm regime is described. The wavelength separation between neighboring lasers is as small as 0.3 nm. A large total wavelength span of 43 nm was obtained without compromising the performance of the lasers. All 140 lasers have nearly the same threshold currents, voltages, and resistances. The techniques used are generic and can be readily extended to both longer and shorter wavelength lasers. The authors also report the first wavelength division multiplexing system experiment using part of this laser array. A BER (bit-error ratio) of 10 ^-9 at 155 Mb/s was obtained with simultaneous operation of four lasers at a wavelength separation of 1.5 nm. Negligible optical and electrical crosstalk was observed between the lasers     

Er3+-Yb3+ and Er3+ doped fiberlasers

Single-mode fiber lasers operating at ~1.57 μm are described. Output powers of >2 mW are reported for laser diode pumped operation. Direct comparison is made between fiber lasers using sensitized erbium (Er³⁺ and Yb³⁺) and erbium on its own. The performance of Er³⁺-Yb³⁺ fiber lasers is analyzed in more detail as a function of fiber length. Both CW and Q-switched operations are studied and the results obtained demonstrate that practical sources at 1.5 μm are available from diode pumped Er³⁺ -Yb³⁺ systems     

Ridge formation for AlGaAs GRINSCH lasers by Cl2reactive ion etching

Optical storage applications for AlGaAs power lasers require single-mode laser operation and well-controlled beam divergence. For AlGaAs GRIN separate confinement heterostructure (GRINSCH) ridge lasers, these optical characteristics are sensitive to the precise ridge geometry of the laser. Directional reactive ion etching with Cl₂ and in situ monitoring of the etch with highly attenuated laser interferometry provide the excellent process control required during formation of the ridge. The process is described, and results are presented for lasers that were fabricated using this technique     

A 500 MHz tunable CO2waveguide laser for optical pumping

A long-pulse CO2waveguide laser is described, which can be single frequency tuned over 500 MHz in about 80 lines. A peak power reaching 125 W at line center and 85 W at the tuning edge in the strongest lines makes the laser ideally suited for optically pumped FIR lasers. New FIR lines have been observed by pumping CH3OH in absorptions located up to 268 MHz from the CO2line center. FIR wavelengths have been measured, identified, and compared to calculations at a level of relative accuracy of5 cdot 10^{-5}.     

End-pumped Nd:LaF3 and Nd:LaMgAl11O19 lasers

Nd:LaF₃ and Nd:LaMgAl₁₁O₁₉ (LMA) are promising candidates for pulsed diode-laser-pumped lasers because they have relatively long upper state lifetimes and large absorption bandwidths compared to other Nd³⁺ doped materials. Crystal growth of LMA and the spectroscopic properties of both materials are described. Continuous-wave (CW) end-pumped lasers have been demonstrated in these materials using a Ti:Al₂O₃ laser to simulate the diode-laser pump source. Slope efficiencies of 47% for Nd:LaF₃ and 32% for Nd:LMA were obtained. The results for Nd:LaF₃ are typical for end-pumped, CW, Nd³⁺ lasers; the lower slope efficiency for Nd:LMA is attributed to excited-state absorption     

FM mode-locked high-pressure CW RF-excited CO2 waveguidelaser

The authors report the results from a study of a FM mode-locked continuous-wave (CW) RF-excited CO₂ waveguide laser operated at 0.25-2 atm gas pressures. It is shown that electrooptic FM modulations can be efficiently used to mode lock a CW CO₂ laser. The combination of a high gas pressure and a high modulation frequency makes it possible to generate pulses which are substantially shorter than those previously reported for CW mode-locked CO₂ lasers. A theoretical approach is used for simulation of the FM mode-locked laser. The experimental pulses of a few hundred picoseconds FWHM are considerably shorter than previously reported for CW mode-locked CO₂ lasers. The experimental results are compared with the results of numerical calculations using a frequency domain simulation model     

Optically pumped CW dimer lasers

Bound-bound electronic transitions in simple molecules are generally suited to realize efficient multiline laser oscillation in the visible and ultraviolet spectral region. By means of optical excitation with argon and krypton lasers, CW laser oscillation could be obtained for various homonuclear diatomic (dimer) molecules such as Li2, Na2, K2, Bi2, S2, Te2, and I2, with emission of several hundred laser lines in the spectral range of about 400-1350 nm. The principles of these lasers and the general dependence of threshold and output power on temperature, pressure, length of vapor zone, and some other parameters is discussed. To achieve satisfactory CW operation, low quenching losses for the upper laser level population and a sufficiently fast relaxation of the population of the lower laser level are necessary. Under optimum operation conditions, efficiencies up to 15 percent, multiline output powers up to 400 mW, and single line-single frequency output powers up to 200 mW were achieved. These dimer lasers are three-level laser systems. In case of coherent optical excitation, two-photon or Raman-type processes contribute to the amplification process. Due to these mechanisms the forward direction is strongly favored and in a ring laser system spontaneous unidirectional oscillation is obtained. By means of a suitable three-level model, analytical and numerical calculations of gain profiles are performed and compared with experiments. These optically pumped molecular lasers are suited for various spectroscopic and kinetic investigations, for frequency standards or as simple and efficient systems to convert pump laser radiation into other spectral regions.     

High-speed 1.5-μm compressively strained multi-quantum wellself-aligned constricted mesa DFB lasers

A great improvement in the high-speed characteristics for compressively strained multi-quantum-well (MQW) distributed-feedback (DFB) lasers with self-aligned constricted mesa structures is described. Negative wavelength detuning is an important factor in making possible the extraction of potential advantages for the compressively strained MQW DFB lasers. A 17-GHz bandwidth, which is the highest among the 1.5-μm MQW DFB lasers, is demonstrated. A wavelength chirp width of 0.42 nm at 10 Gb/s is obtained due to a reduced linewidth enhancement factor that has a magnitude of less than 2. Nonlinear damping K factor in a DFB laser with 45-nm negative detuning has drastically decreased to 0.13 ns, about half of that for unstrained MQW lasers. This is mainly due to an enhanced differential gain as large as 6.9×10 ^-12 m³/s. The estimated intrinsic maximum bandwidth is 68 GHz     

Vertical-cavity surface-emitting laser diodes fabricated by in situdry etching and molecular beam epitaxial regrowth

The authors report the first buried active region vertical-cavity surface-emitting laser diodes fabricated using in situ dry etching and molecular beam epitaxial regrowth. The laser emissions of the etched/regrown devices persist over a greater current range and exhibit maximum output powers larger than air-post lasers. The lasers are anisotropically etched into the lower monolithic distributed Bragg reflector using an electron cyclotron resonance SiCl₄ plasma etch. After transfer in ultra-high vacuum, epitaxial AlGaAs current blocking layers are regrown around the etched mesas. Polycrystalline deposition on the SiO₂ mask is removed by reactive ion etching to allow electrical contact and top surface emission. The etched/regrown laser characteristics demonstrate efficient current confinement and low thermal impedance. The vacuum integrated processing described offers the prospect of further device performance enhancements and greater functionality     

Far-infrared raman laser with high intensity laser pumping

Theoretical and experimental results are presented for a pulsed far-infrared (FIR) molecular gas laser with high intensity laser pumping. In these FIR lasers, high intensity pumping is found to produce stimulated Raman emission at very large offsets (up to 30 GHz) from resonance with the intermediate state. A theoretical, density matrix model is developed for these lasers to account for simultaneous Raman emission on rotational levels in the ground and excited vibrational states (double Raman resonance). This theoretical approach is necessary in the case of off-resonant, high intensity pumping. Theory predicts the FIR emission frequency, the FIR laser gain, and the pump threshold intensity as a function of pump laser frequency. Experimental results are obtained onP-,Q-, andR-branch transitions in¹²CH3F and¹³CH3F using a single-mode, grating tuned CO2TEA pump laser with an intensity of up to 40 MW/cm². Good agreement is obtained between theory and experiment for the observed values of FIR emission frequency and pump threshold intensity. These results indicate that a widely tunable (150-1200 mum), pulsed FIR CH3F laser could be constructed with a tunable, multiatmospheric CO2pump laser of modest power (about 2-5 MW).     

Quantum-well heterostructure lasers

The various features peculiar to the operation of quantum-well semiconductor lasers are described and illustrated with data on single- and multiple-quantum-well AlxGa1-xAs-GaAs heterostructures grown by metalorganic chemical vapor deposition (MO-CVD). Photo-pumped and p-n diode lasers (injection lasers) are described that are capable of continuous room temperature (CW 300 K) operation. The basic problems of carrier collection, thermalization, and quantum-well band filling are considered and have made clear the limits on single quantum-well laser operation and how these can be overcome with multiple quantum-well active regions. The idea that the steplike density-of-states of a quantum-well heterostructure can improve the operation of a semiconductor laser is shown to be valid. Also, it is shown that phonon participation in the operation of a quantum-well laser, which was not anticipated, is a major (even dominant) effect, with perhaps the phonon emission itself in the compact active region being stimulated. Besides the obvious freedom that quantum-well layers offer in how the active region of a semiconductor laser can be designed, quantum-well lasers are shown to exhibit a lesser sensitivity of the threshold current density on temperature, which is explained in terms of the step-like density-of-states and the disturbed electron and phonon distributions in the quantum-well active regions. Values as high assim437degC have been obtained for T0in the usual expressionJ_{th}(T) = J_{th}(0) exp (T/T_{0}). Since photopumped multiple-quantum-well MO-CVD AlxGa1-xAs-GaAs heterostructures have operated as CW 300 K lasers with only 5-10 mW of photoexcitation (uncorrected for focusing and window losses,lambda sim 5145Å), it is suggested that quantum-well laser diodes can be made that will operate at ∼1 mA or even less excitation.     

Structure-dependent threshold current density for CdZnSe-basedII-VI semiconductor lasers

The optical gain and threshold current density of CdZnSe-based semiconductor lasers are calculated theoretically with strain and quantum confinement effects taken into account. Both diffusion and drift components are incorporated into the calculation of leakage current. Optimized structures are obtained for CdZnSe-based lasers with different structures through minimizing the threshold current density. A minimum current density of about 200 A/cm² is obtained for a Cd_0.2Zn_0.8Se/ZnS_0.06Se_0.94 /Zn_0.75Mg_0.25S_0.42Se_0.58 modified MQW laser