Enhancement of the efficiency and specific output energy of an electric-discharge CO laser by intensification of heat exchange with the walls

Abstract

We report on the single and double multiphoton ionization of ground state Sr atoms observed in an atomic beam experiment with laser pulses of ∼5 ns duration, maximum intensity ∼4 × 10 11 W cm −2 and within the 710-740 nm wavelength range. The Sr + spectrum consists of two strong lines originating from three-photon resonant four-photon ionization of bound states, a number of weak autoionizing resonances and a broad line due to four-photon excitation of the doubly excited 5p 2 1 S 0 state. The latter, along with a strong, broad and structured spectral feature, is also evident in the wavelength dependence of the doubly charged Sr 2+ ion. A weakly evident but reproducible inflection point ('knee' structure) appears in the intensity dependence of the Sr 2+ yield at the location of the 5p 2 1 S 0 resonance. A complementary fluorescence experiment revealed the accumulation of population in the 5p 1/2 , 3/2 , 6s 1/2 and 5d 3/2 , 5/2 excited Sr + states during the laser pulse. All fluorescence signals depend on laser wavelength in a manner similar to the recorded Sr + spectrum. The population accumulation in the 5p 1/2 , 3/2 ionic states unambiguously proves the absorption of two photons above the first 5s 1/2 atomic threshold while that of the 5d 3/2 , 5/2 and 6s 1/2 ones suggest the absorption of at least two more. Since under our laser pulse duration and intensity the absorption of such a number of photons in an unstructured continuum is highly improbable, it may be concluded that the process is mediated by dense manifolds of near-resonant doubly excited states, their role in the dynamics of laser-atom interaction under our conditions being far more crucial than in studies conducted using intense ultrashort pulses.

Energy conversion in high enthalpy flows and non-equilibrium plasmas

“…lasers known that are scalable to very high steady infrared powers. Efficiencies as high as 50% were reported by Grigor'yan et al [30] and powers up to 200 kW have been obtained by Dymshits et al [31] in c.w. systems operating on the fundamental bands.…”

Continuous-wave electrically excited carbon monoxide laser operating on first overtone infrared bands: 2.5- to 4.0-microns kinetic modeling and design

“…The OSU and Bonn CO lasers are usually operated on fundamental bands with the requirement of some substantial output on the v=1-O component. This last requirement limits the power produced in the lasers to '-1 5 W. However, when operated without this constraint, they have produced powers above 100 W, into the range achieved in [2]. The tubes are made of Pyrex glass, and have a jacket for liquid nitrogen for wall cooling, and an outer vacuum jacket for thermal insulation.…”

“…The code has been developed for this study from OSU master equation modeling codes for CO electrical plasmas. As discussed below, the code has been validated by comparison with experimental performance data on efficient CO lasers, including the discharge tube configurations used by Grigoryan [2] and at OSU [1 0]. We discuss the modeling code and the validation results in the following section.…”

“…We propose to use laser discharge tubes of the design widely used for CO lasers at the Nonequilibrium Thermodynamics Laboratories at Ohio State [10] and at the Institute for Applied Physics at the University of Bonn [1 1]. This tube design is a combination of features designed by these groups and is partly based on earlier work by Grigoryan at the University of St. Petersburg [2]. The Grigoryan design, as noted previously, holds the record for maximum c.w.power on the fundamental CO bands for a table-top device (1.5 m active length), as well as the maximum efficiency from any c.w.…”

“…Efficiencies as high as 50% and c.w. powers of near-megawatt level have been achieved [2,3]. Early FO CO systems reported much lower efficiencies [ 1%], and it was believed that development to much higher efficiencies would be impeded by the relatively low gain on many of the overtone transitions, and loss due to parasitic lasing on the higher gain fundamental transitions.…”