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Beam profile measurements have been made as a function of time within the laser pulse and C2F5I pressure. Measurements indicate that the profile is determined directly by the optical excitation volume, produced by the solar simulator, and that media distortion plays a minor role compared to the build up of quenching species during the lasing pulse.
A phase-locked injection laser array is described which utilizes variations in spacing of identical lasing elements to vary the coupling between them. A coupled-mode analysis indicates that excellent matching of fundamental array mode to a uniform gain distribution can be obtained. Observation of the array emission patterns confirms the results of the coupled-mode analysis.
The scaling of blackbody pumped lasers to large powers is being studied. The computational results show the possibility of high pressure transverse flow blackbody pumped lasers. A nonsteady technique with metal shims heated rapidly to 1500 K as the blackbody pumping source is being used to carry out the experiment. Fast temperature rise of the shims creates pressure waves inside the laser cavity which destroy the resonance of the cavity. A new design with rectangular quartz tubing inside the cavity to prevent the waves from reaching the lasing region is under construction.
The bandwidths of the discrete spectral components of the auroral kilometric radiation can sometimes be as narrow as 5 Hz. Since this would imply an apparent source thickness of substantially less than the wavelength, it is inconsistent with the previous explanation for such discrete components based simply upon vertical localization of a cyclotron source. Instead, such narrow bandwidths can only be explained by radio lasing.
Far-infrared CW radiation of 1.25 watts has been obtained at the 119 micron methanol line with a CO2 pump power of 125 watts, and the maximum frequency fluctuation of the free running laser is measured to be less than + or - 100 kHz per hour. Reflecting optics have been used, when possible, to minimize CO2 degradation, and the frequency stability is ensured by cooling the input and output couplers. The input and output assemblies within the lasing medium are enclosed to minimize the external effects on the cavity length and to eliminate the mechanical instabilities associated with the use of bellows. The vibrational bottle-neck is broken by cooling the resonator wall to 5 deg and adding He as the buffer gas.
If the auroral kilometric radiation (AKR) were generated by loss cone lasing on closed field lines, as has been proposed, then it should cause substantial auroral precipitation by the pitch angle scattering of energetic electrons into the loss cone. A rough estimate for this precipitation, based upon the observed AKR amplitudes, would imply a flux of at least 2 x 10 to the 8th el/sq cm sec over the projected ionospheric footprint of an individual laser and, if most of the AKR radio lasers occupied the same electron drift an L shell, an arc of 8 km width with a minimum average flux of roughly 10 to the 9th el/sq cm sec. It is believed that this will account for auroral arcs and other aspects of auroral electron precipitation.
Optical pumping of a holmium:yttrium lithium floride (Ho:YLF) crystal with a 790-nm continuous-wave diode-laser array has generated 56 mW of 2.1-micron laser radiation with an optical-to-optical conversion slope efficiency of 33 percent while the crystal temperature is held at 77 K. The lasing threshold occurs at 7 mW of input power, and laser operation continues up to a crystal temperature of 124 K.
Laser threshold of 100 solar constants achieved. Using two xenon-arc solar simulators, lasing achieved with pentafluoroethyl iodide, a new alkyl iodide, at laser threshold of only 100 solar constants. Solar laser had lowest threshold observed to date. Output power and energy 350 mW and 45 mJ.
For more than thirty years the intense decametric radio emissions from Jupiter (DAM) and the corresponding auroral kilometric radiation from the Earth (AKR) have remained major radio science mysteries. Part of the problem, aside from their inherent complexity, has been the difficulty of measuring their source location and emission properties from limited observations. Progress has been made on this problem by locating the source directly, i.e., by analysis of the faraday rotation observed with Voyager as the wave path crossed the Io plasma torus, and indirectly by comparing the peak frequencies of the decametric emission with that at the foot of the Io flux tube. Progress was also made on the general question of how the emissions originate by finding properties of both the AKR and DAM which would imply emission by natural radio lasing.
For the first time lasers operating at 1.93 microns were demonstrated. The lasers were fabricated by Vapor Phase Epitaxial (VPE) growth techniques currently used for the fabrication of high power lasers at 1.3 microns. The structure of these laser diodes consisted of compositionally graded, sulfur-doped InAsP, grown on an InP substrate; a constant-composition n+InAs(0.27)P(0.73) layer, which is the first cladding layer; an In(0.66)Ga(0.34)As layer, which is the active region, and a second InAs(0.27)P(0.73) layer. The devices were oxide-stripe DH lasers (gain-guided only). The best devices had 80 K lasing thresholds in the range of from 80 to 150 mA, and T sub o (below 220 K) in the range of 60 to 90 K. The highest observed temperature of oscillation was 15.5 C. The highest observed power output at 80 K was in the range of 3 to 5 mW. The calculated delta I/delta T was 4.4 A/K. As a part of the materials development, PIN homojunction detectors having the band edge near 1.93 were also fabricated. The best devices (100 micron diameter, mesa structure) exhibited room temperature dark currents in the range of from 20 to 50 nA and had QE at 1.93 microns in the range of 35 to 40 percent. In addition to the device results, the InGaAs-InAsP materials system was extensively investigated and low defect density layers can now be grown allowing for significant device performance improvement.
Performances of Nd in various hosts including Nd:YAG, Nd:YLF, Nd:BEL, and Nd:Cr:GSGG were characterized and compared for operation on the nominal 1.06 micron and 1.33 micron transitions. Comparison included continuous mode operation, normal mode operation, Q-switched operation, and gain measurements. Continuous lasing of Nd:Cr:GSGG under lamp pumping is reported for what may be the first time. Characterization included operation with different mirror reflectivities to obtain the internal losses, measurement of the upper laser level lifetime, measurement of the beam quality of the lasers operating under nominally similar circumstances, and measurement of the wavelength. These measurements should provide a comparison of the various Nd hosts under similar circumstances for a wide variety of operational modes and at both wavelengths of interest.
An experimental investigation of the dependence of intracavity absorption on factors including transition strength, concentration, absorber path length, and pump power is presented for a CW dye laser with a narrow-band absorber (NO2). A Beer-Lambert type relationship is found over a small but useful range of these parameters. Quantitative measurement of intracavity absorption from the dye laser spectral profiles showed enhancements up to 12,000 (for pump powers near lasing threshold) when compared to extracavity measurements. The definition of an intracavity absorption coefficient allowed the determination of accurate transition strength ratios, demonstrating the reliability of the method.
The output emission of a short CH3F metallic waveguide laser pumped by an injection-locked CO2 transversely excited atmosphere laser is studied experimentally. The output is found to be extremely unpredictable when lasing occurs in both the excited and ground vibrational states on two separate transitions (496 and 452 microns, respectively). The dynamics and sensitivity to initial conditions are explained in terms of two Lorenz lasers with pump coupled population inversions.
The mode-medium instability of an active medium in an unstable resonator is investigated. The asymptotic solution due to Horwitz (1973), valid for large Fresnel numbers in an empty cavity, is modified by introducing gain/phase sheets in front of the resonator mirrors. The effect of medium coupling to the mode in the cavity is obtained by introducing a general time-independent Green's function in the Fox-Li (1961) formulation. The time evolution is then obtained by repeated integration of the beam propagation in the cavity. The diffractive terms are shown to grow rapidly at the expense of the geometric term. This instability responsible for the deterioration of the beam quality is studied numerically for a CO2 lasing system as an example.
An iodine photodissociation laser was pumped by a long Ar arc as the solar simulator to produce a 10-W CW output. Continuous lasing for 1 h was achieved with a flow of the laser material n-C3F7I. The 10-W CW output is the highest produced to date and establishes the feasibility of developing a solar-pumped laser for space power transmission.
The current status of NASA Langley efforts to develop solid-state lasers for use in the Lidar Atmospheric Sounder and Altimeter (LASA) of the Space Station Earth Observing System is surveyed. The types of observations to be performed with LASA are listed, and the parameters of presently available lasers are compared with the LASA baseline goals: 2 kW output power; 500 kg weight; tunability to 727, 760, and 943 nm to within 500 fm; high spectral purity; efficiency greater than 3 percent; energy about 1 J/pulse, pulse length less than 100 nsec, and lifetime greater than 108 shots. The use of sensitized flashlamp-pumped laser materials or diode-laser pumping to improve performance is discussed, and particular attention is given to materials research on Ti:sapphire lasers, studies of higher-efficiency detectors, and the LASE and LITE airborne lidar and DIAL experiments.
The spectral linewidth of a long distributed feedback (DFB) laser above threshold at high output power is investigated theoretically. Longitudinal spatial hole burning (LSHB) is shown to have important effects on the lasing characteristics and the broadening of linewidth. A four-wave coupled mode equation is developed to describe the LSHB phenomenon. The threshold gain and the carrier distribution are solved self-consistently above threshold at various output powers. The simulation results show that the power-linewidth product can increase by a factor greater than 2 due to LSHB for long DFB lasers. This theory has important implications on the limits of linewidth reduction by increasing the length of DFB lasers and on possible future device design for coherent optical systems.
Experimental process makes films with interesting magnetic and magneto-optical properties. Films of dilute magnetic semiconductor alloy Cd1-xMnxTe deposited on glass and GaAs substrates by metalorganic chemical-vapor deposition (MOCVD). Devices made with Cd1-xMnxTe films known to exhibit strong photoluminescence, stimulated emission, and magnetically-tunable lasing action. In addition, energy-band gaps of such material tailored by altering its composition - property giving flexibility in development of high-efficiency cascade solar photovoltaic cells. Performs at atmospheric pressure, resulting in more-uniform films, covering larger area, and enabling higher production rate.