Ring resonators have unique properties that are sometimes desirable. Spatial hole burning is eliminated. Beam transformation, such as image rotation which may reduce the magnitude of certain aberrations, can be implemented in a traveling-wave region. There is a drawback, however. As usually constructed, a ring resonator has half as many passes through the gain medium as can be achieved with a standing-wave resonator. This may have a detrimental effect on laser efficiency. We have constructed a type of ring resonator that allows counterpropagating collinear passes through the gain medium, while there is also a section with a unidirectional beam. The resonator includes a polarizing beam splitter. The linear polarization is transformed to the orthogonal state by optical elements at the two ends of the region with counter-propagating beams. The beams passing through the gain medium in opposite directions are linearly polarized with orthogonal states.
A computer code to calculate the output power and disk temperature distribution for a spinning disk laser has
been developed. Calculated values agree well with experiment. The surfaces of the Nd:YAG rotating disk pass
close to two water-cooled plates. A thin gap, filled with gas, separates each plate from the disk. For an Nd:YAG
disk, results are given for a 50 μm gap filled with <b>He</b>.
Experimental results describing pulsed lasers operating near 3.9 μm on the Ho<sup>3+ </sup>(<sup>5</sup>I<sub>5</sub>-<sup>5</sup>I<sub>6</sub>) transition in highly-doped (> 10 at. %) barium yttrium fluoride (BaY<sub>2</sub>F<sub>8</sub> or BYF) will be presented. The <sup>5</sup>I<sub>5</sub> manifolds in Ho:BYF were pumped using a flashlamp excited, free-running Cr:LiSAF laser tuned to the Ho<sup>3+</sup> absorption peak near 889nm. Ho<sup>3+</sup> concentrations of 10%, 20%, 30% and 40% in BYF were lased in a simple end-pumped resonator. Some similar data was also obtained in 10% and 20% Ho:YLF. The highest 3.9 μm pulse energy obtained in the comparative study was 55 mJ (at ~10% optical-to-optical efficiency) using the 30% Ho:BYF crystal. A dual end-pumped laser in 30% Ho:BYF was also demonstrated, providing a pulse energy of 90 mJ in a near diffraction limited beam (M<sup>2</sup> ~ 1.2). Emission decay data was taken to shed light on the observed dependence of laser efficiency on holmium concentration and excitation density. The lifetimes of both lasing levels (<sup>5</sup>I<sub>5</sub> and <sup>5</sup>I<sub>6</sub>) deviate rather significantly from their low-concentration values. Plausible energy transfer processes that may be responsible for the observed trends in the laser and emission data will also be discussed.
Approximate calculations of the temperature distribution of a rotating-disk solid-state laser are presented. The surfaces of the Nd:YAG or Nd:glass rotating disk pass close to two water-cooled plates. A thin gap, filled with gas, separates each plate from the disk. For an Nd:YAG disk, temperature distributions are given for a 50 μm gap filled with He, for a 50 μm gap filled with air, and for the case in which the thermal conductivity of the Nd:YAG dominates the problem. Calculated results for an Nd:glass disk are compared with a temperature profile obtained from a rotating-disk laser.
Results of parametric studies on a high efficiency, 2.7 micrometers atomic bromine laser, produced by photolyzing IBr with 532 nm radiation, are presented. Concurrently, the results of a rate equation computer model show excellent agreement with experimental measurements.
A Q-switched Nd:YAG laser generating 160 mJ in 60 ns at 1.3 micrometers has been shifted to 2.9 micrometers by Raman conversion in hydrogen. The energy of the 2.9 micrometers photons is insufficient to undergo further Stokes shifts. Thus the first Stokes line is the terminal wavelength for this process. While terminal Stokes components have been reached in previous Raman shifting studies, these components have always been the result of multiple Stokes shifts. In a single pass configuration photon conversion of up to 0.37 was realized. Conversion into anti-Stokes lines of up to third order was observed, albeit at insignificant energies. With the addition of an unoptimized resonator the photon conversion rose to 0.49. The pressure dependence of Stokes conversion was also investigated. The data show a smooth increase in output followed by saturation. This is in accordance with conversion into a single terminal Stokes lines. However, in contradiction with theory, the pump linewidth was observed to matter a great deal. Amplified elastic or near elastic scattering is suggested as an explanation for this result. Overall, the success of this work bodes well for forthcoming attempts to obtain tunable mid-IR radiation by means of a terminal first Stokes shift.
Population inversions in small gas-phase molecules are produced by optical pumping of vibrational overtone transitions. Efficient frequency down conversion of the pump radiation is obtained by lasing on the inverted transitions. The performance of the lasers is governed by kinetic relaxation and energy exchange processes. The effect of these processes on the ultimate scalability of this class of laser will be discussed.
This experimental research program is designed to assess the possibility of using gas-phase optically pumped lasers (OPL) as efficient, frequency-agile mid-infrared sources. The eventual goal will be to incorporate efficient diode lasers into the pumping step, either by direct frequency stabilized diode pumping or by pumping with diode-pumped solid state lasers. In this paper, we discuss experiments on a optically pumped hydrogen fluoride laser. Rotation- vibration transitions in the (2,0) band around 1.3 micrometers are pumped, and lasing is observed on (2,1) band transitions near 2.7 micrometers .