Ultrafast 2DIR comparison of rotational energy transfer, isolated binary collision breakdown, and near critical fluctuations in Xe and SF solutions.

The density dependence of rotational and vibrational energy relaxation (RER and VER) of the NO ν asymmetric stretch in dense gas and supercritical Xe and SF solutions for near critical isotherms is measured by ultrafast 2DIR and infrared pump-probe spectroscopy. 2DIR analysis provides precise measurements of RER at all gas and supercritical solvent densities. An isolated binary collision (IBC) model is sufficient to describe RER for solvent densities ≤ ∼4M where rotational equilibrium is re-established in ∼1.

Two-dimensional infrared spectroscopy from the gas to liquid phase: density dependent J-scrambling, vibrational relaxation, and the onset of liquid character.

Ultrafast 2DIR spectra and pump-probe responses of the NO ν asymmetric stretch in SF as a function of density from the gas to supercritical phase and liquid are reported. 2DIR spectra unequivocally reveal free rotor character at all densities studied in the gas and supercritical region. Analysis of the 2DIR spectra determines that J-scrambling or rotational relaxation in NO is highly efficient, occurring in ∼1.

Measurements of cesium mixing and quenching cross sections in methane gas: understanding sources of heating in cesium vapor lasers.

Accurate modeling of the operation of diode-pumped alkali lasers is a critical step toward the design of high-powered devices. We present precision measurements for the Cs-CH 6P → 6P mixing cross section and the 6P → 6S quenching cross section, which are important parameters in understanding the operation and, in particular, the heat generated in a cesium vapor laser. Measurements are carried out using ultrafast laser pulse excitation and observation of fluorescence due to collisional excitation transfer in time is done using the technique of time-correlated single-photon counting.

Examination of potassium diode pumped alkali laser using He, Ar, CH and CH as buffer gas.

We examined the performance of a potassium diode pumped alkali laser (K DPAL) using He, Ar, CH, CH and a mixture of He and CH as a buffer gas to provide spin-orbit mixing of the 4P and 4P states of Potassium atoms. We found that pure helium cannot be used as an efficient buffer gas for continuous wave lasing without using a flowing system with a considerable flow speed of about 100 m/s. In contrast, using a small amount of methane (10-20 Torr) mixed with helium, continuous wave lasing can be achieved using very moderate flow speeds of about 1 m/s.

Conformation-specific spectroscopy of capped, gas-phase Aib oligomers: tests of the Aib residue as a 3-helix former.

The conformational preferences of a series of capped peptides containing the helicogenic amino acid aminoisobutyric acid (Aib) (Z-Aib-OH, Z-(Aib)-OMe, and Z-(Aib)-OMe) are studied in the gas phase under expansion-cooled conditions. Aib oligomers are known to form 3-helical secondary structures in solution and in the solid phase. However, in the gas phase, accumulation of a macrodipole as the helix grows could inhibit helix stabilization.

Modeling of pulsed K diode pumped alkali laser: Analysis of the experimental results.

A simple optical model of K DPAL, where Gaussian spatial shapes of the pump and laser intensities in any cross section of the beams are assumed, is reported. The model, applied to the recently reported highly efficient static, pulsed K DPAL [Zhdanov et al, Optics Express 22, 17266 (2014)], shows good agreement between the calculated and measured dependence of the laser power on the incident pump power. In particular, the model reproduces the observed threshold pump power, 22 W (corresponding to pump intensity of 4 kW/cm), which is much higher than that predicted by the standard semi-analytical models of the DPAL.

Efficient potassium diode pumped alkali laser operating in pulsed mode.

This paper presents the results of our experiments on the development of an efficient hydrocarbon free diode pumped alkali laser based on potassium vapor buffered by He gas at 600 Torr. A slope efficiency of more than 50% was demonstrated with a total optical conversion efficiency of 30%. This result was achieved by using a narrowband diode laser stack as the pump source.