Harold C. Miller

Measurement of the radiative lifetime of O2(a1Δg) using cavity ring down spectroscopy

Abstract Cavity ring down spectroscopy has been used to detect the weak a1Δg−X3Σg− electronic transition in oxygen and to obtain a measurement of the radiative lifetime of the a1Δg state. (0,0) band transitions near 1274 nm were scanned using the frequency-doubled output of a tunable OPO system. Pressure-broadened linewidths were measured, and a FWHM-broadening coefficient of 5.5(5) MHz/Torr was obtained. Analysis of the ring down traces provided a measurement of the line strength of an individual rovibronic transition. The Einstein A-coefficient of the a1Δg state was calculated using branching ratios determined from the Honl–London factors. The A-coefficient obtained is 2.3(3)×10 −4 s −1 , corresponding to a radiative lifetime of 4300(500) s ( ∼72 min ). This value is in agreement with those reported by Badger et al. (2.58×10 −4 s −1 ) and Spalek et al. (2.24(40)×10 −4 s −1 ). In addition, a value of 2.77(8)×10 −45 cm 5 / molecule was obtained for the background collisional absorption coefficient for oxygen at 1274 nm.

Optically pumped mid-infrared vibrational hydrogen chloride laser

The results of an experimental investigation of an optically pumped vibrational laser in HCl are reported. Two different excitation sources were used: a Nd:yttrium–aluminum–garnet laser pumped optical parametric oscillator and a Raman shifted alexandrite laser. Overtone pumping on the (2,0) and (3,0) bands was employed to produce laser oscillation on the (3,2) and (2,1) bands near 3.8 μm. We also developed a model for the optically pumped laser and compare predictions of the model to the observed behavior of the laser. The photon efficiency of the HCl laser was found to be approximately 60%, consistent with model predictions and with previous optically pumped hydrogen halide lasers.

A laser beam quality definition based on induced temperature rise.

Laser beam quality metrics like M(2) can be used to describe the spot sizes and propagation behavior of a wide variety of non-ideal laser beams. However, for beams that have been diffracted by limiting apertures in the near-field, or those with unusual near-field profiles, the conventional metrics can lead to an inconsistent or incomplete description of far-field performance. This paper motivates an alternative laser beam quality definition that can be used with any beam. The approach uses a consideration of the intrinsic ability of a laser beam profile to heat a material. Comparisons are made with conventional beam quality metrics. An analysis on an asymmetric Gaussian beam is used to establish a connection with the invariant beam propagation ratio.

High-pulse-energy 3.9-μm lasers in Ho:BYF

Experimental results describing pulsed lasers operating near 3.9 μm on the Ho3+ (5I5-5I6) transition in highly-doped (> 10 at. %) barium yttrium fluoride (BaY2F8 or BYF) will be presented. The 5I5 manifolds in Ho:BYF were pumped using a flashlamp excited, free-running Cr:LiSAF laser tuned to the Ho3+ absorption peak near 889nm. Ho3+ 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 (M2 ~ 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 (5I5 and 5I6) 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.

Rotating-disk solid state lasers: thermal properties

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.

Two Micron Diode-Pumped Laser Operation of Tm,Ho:BaY2F8>

Diode-pumped Tm, Ho:BaY2F8 was operated as a room-temperature two micron laser. Laser results and various spectroscopic parameters are reported.

Stable ring resonator with bidirectional passes through the gain medium

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 laser beam quality definition based on induced temperature rise: erratum

An erratum is presented to correct an error in an equation used to determine laser beam quality from power-in-the-bucket curves.

Spinning disk solid-state lasers, computer simulation

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 He.

Near-diffraction limited 65 W Nd:YLF laser

One of the primary challenges to obtaining diffraction-limited performance in high-power solid state lasers is compensating for the thermally-induced optical effects[i].