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Lawandy, N. M.

Publications and source records attributed to Lawandy, N. M..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1986

Nonlinear infrared generation in alkali metal vapors: Steady state susceptibilities and dynamic behavior. Effective relaxation rates and preliminary Raman gain predictions for the Cs system

Effective relaxation rates for atomic cesium pumped by doubled Alexandrite radiation are presented. Laser radiation levels are 8S 1/2 and 9S 1/2; resonance levels 3 = 8P 1/2 and 8P 1/2, respectively. In addition, Raman gain is represented in two graphs which plot chi per atom (10 to the -13 power) at Raman peak versus the infrared wave number per centimeter and the corresponding doubled Alexandrite wave number. One graph covers resonance level 8P, the other 9P; in both cases cesium is pumped with a peak pulse height of 0.5 MW in a 200 micron diameter spot size.

Lawandy, N. M.↗
NASA NTRS1986

Theoretical studies of Resonance Enhanced Stimulated Raman Scattering (RESRS) of frequency doubled Alexandrite laser wavelengths in cesium vapor

This work focused on understanding the effects of arbitrary transverse and longitudinal relaxation rates on the susceptibilities of coherently driven three-level systems. The approximation of a single relaxation rate often made in previous work is strongly invalidated by the variation in the spontaneous emission lifetime between various atomic level pairs in systems such as cesium. It is of great importance to the problem of nonlinear infrared generation to determine the dependence of both real and imaginary susceptibility on relaxation rates. The imaginary susceptibility on the pump transition determines the absorption of pump photons and the imaginary susceptibility on the laser transition determines the spectral dependence of the gain. This is of particular importance for pure Raman emission (i.e., absorption at linecenter of the gain transition) as it determines the tunability characteristics we are aiming to predict. The real susceptibility is important when cavities are used at the signal field as this will determine the loaded resonance of the Raman oscillator. Researchers show that in some cases which result from having different relaxation rates mode splitting may result, allowing more than one frequency to have the same Raman wavelength, possibly resulting in a temporal instability.

Lawandy, N. M.↗
NASA NTRS1986

Theoretical studies of Resonance Enhance Stimulated Raman Scattering (RESRS) of frequency doubled Alexandrite laser wavelengths in cesium vapor

It is well known that the presence of a real atomic level which is nearly resonant with the pump field can greatly enhance the Raman emission cross section. In order to accurately calculate the Raman gain in systems where resonance enhancement plays a dominant role, expressions for the pump and signal susceptibilities must be derived. These expressions should be valid for arbitrary field strengths in order to allow for pump and signal saturation. In addition, the theory should allow for arbitrary longitudinal and transverse relaxation rates. This latter point is extremely vital for three level atomic systems such as the alkali earth metals since they do not have population reservoirs and can have widely varying spontaneous lifetimes on the three pertinent transitions. Moreover, the dephasing rates are strong functions of electron states and are therefore also different for the three coupled pairs of levels. These considerations are not as important when molecular systems are concerned since the large reservoir of rotational states serve to produce essentially equal longitudinal recovery rates for the population of the three levels. The three level system with three arbitrary longitudinal and transverse relaxation rates was solved. There is no need for setting either pair of rates equal and the expressions are valid for arbitrarily strong fields.

Lawandy, N. M.↗
NASA NTRS1982

Collisional narrowing in the optically pumped CH3OH and CH3F lasers

The gain linewidth of the optically pumped CH3F laser is observed to narrow and rebroaden with the addition of He. In addition, the same effect is observed in the CH3OH laser with the addition of the polyatomic buffer gases SF6 and CS2. These results offer conclusive evidence of the Dicke narrowing phenomena in these inverted pure rotational transitions. The effect is observed using a high harmonic mixing technique in a Schottky barrier diode.

Lawandy, N. M.↗
NASA NTRS1981

Laser inhibited diffusion in rhodamine-ethanol solutions

The diffusion of rhodamine-6G dye in ethanol is observed to be inhibited by optical pumping by a cadmium laser. The diffusion process is observed as a function of the solution temperature. The relative difference in diffusion coefficients with and without optical pumping is calculated. The effect is interpreted as being due to a stronger solvent-dye interaction in the first excited singlet state of rhodamine-6G.

Lawandy, N. M.↗
NASA NTRS1981

The possibility of vibrational lasing in CD3F

A new lasing mechanism is proposed as a result of the unusual performance characteristics of the 206 micron emission of the CD3F optically pumped molecular laser. The scheme presented is only meant to be suggestive. It is pointed out that most of the CD3F lines are pure rotational. However, the three lines at 206, 201.5, and 247.5 microns are seen as indicating the possibility of vibrational lasing. The 247.5 micron line is thought to be the most likely other candidate of the remaining two. This conclusion derives from the availability of pump power in the 9R10 CO2 laser line vis a vis the strong emission and 0.20 torr optimum operating pressure.

Lawandy, N. M.↗
NASA NTRS1980

Pressure shift in the 170-micron emission of the CW optically pumped CH3OH laser

Pressure shifts of +15 MHz torr were observed in 16(8)-16(7) 170-micron CW CH3OH optically pumped laser emission. The experiments were performed using a harmonic mixing technique in a Schottky diode. The results are explained in terms of a second-order dipole-dipole interaction in a statistical formulation.

Lawandy, N. M.↗
NASA NTRS1980

Energy-transfer mechanisms in the CH3F-SF6 optically pumped laser

The power of an optically pumped CH3F laser operating on the 496-micron line has been doubled with the addition of SF6 without any corresponding increase in pump absorption. It is suggested that a near-resonant energy transfer between CH3F and SF6 followed by SF6 deactivation is the mechanism responsible for the enhancement.

Lawandy, N. M.↗
NASA NTRS1980

Collisional narrowing by polyatomic buffer gases in an optically pumped CH3F laser

The gain linewidth of an optically pumped CH3F molecular laser is observed with the addition of various polyatomic buffer gases. This is interpreted as collisional (Dicke) narrowing. The measurement is the first observation of collisional narrowing by polyatomic buffer gases. It is also the first observation of the effect in a laser oscillator. The effect was observed using a heterodyne mixing technique at the laser emission frequency of 604 GHz. Collision cross sections for SF6-CH3F and CS2-CH3F are obtained.

Lawandy, N. M.↗
NASA NTRS1980

Relaxation oscillations in optically pumped molecular lasers

The observation of relaxation oscillations in both the (C-13)H3F and (C-12)H3F optically pumped lasers is reported. Expressions are derived for the oscillation frequency and its temperature and pressure dependences using a four-level rate equation model. Excellent agreement between measured frequencies and the theory presented is observed. Models are considered for using this phenomenon to determine the rotational and vibrational relaxation mechanisms of the laser gases.

Lawandy, N. M.↗
NASA NTRS1980

Optoacoustic measurement of vibrational-translational /V-T/ rates using a short pulse CO2 laser

A technique for measuring the V-T transfer rates of polyatomic species based on the optoacoustic effect discovered by Bell, Tyndall, and Rontgen (1881) is investigated experimentally. The technique makes use of a coincidental resonance between one of the molecules vibration rotation bands and a CO2 laser line. By this absorption, the molecules can be excited to a known vibrational mode. Since typical time constants for V-T transfer are about 0.00001 sec torr, this method can be used in the pressure region up to 1 torr. The results obtained for CH3F agree with the measurements performed by other techniques.

Lawandy, N. M.↗
NASA NTRS1979

Far-infrared lasing in ruby

The feasibility of submillimeter wavelength (870 GHz) lasing in Al2O3 is discussed. The proposed scheme is based on the pumping of the 2A level of ruby via a ruby laser operating on its R2 line. Lasing is expected on the 2A to E transition of the split E-2 level.

Lawandy, N. M.↗
NASA NTRS1979

Temperature dependence of optically pumped far-infrared /FIR/ laser output power

The temperature dependence of the small signal gain and saturation power are derived using temperature-dependent rates in a four-level model. An expression is developed for the output power of a far-infrared oscillator as a function of temperature for both fixed pressure and fixed density. The results are valid in the regime of homogeneous broadening of the rotational transition and Doppler broadening of the pump transition. It is shown that, for most lasers, both the small signal gain and the saturation power decrease with increasing temperature. These effects have the overall result of increasing output power with decreasing temperatures.

Lawandy, N. M.↗
NASA NTRS1979

Photon reflection at the boundary of an inverted medium

The index change near a quantum transition is shown to cause significant feedback into a gain medium. Criteria are given for the onset of self-lasing in an extended material. The distortion of a reflected pulse is also considered.

Lawandy, N. M.↗
NASA NTRS1979

Approximate analytic solutions for the optical pumping of fluorescent dyes

A general technique for solving a system of rate equations describing the interaction of an electromagnetic field and a molecular system is presented. The method is used to obtain approximate time-dependent solutions for the upper-level populations of fluorescent dyes in the presence of a pump field.

Lawandy, N. M.↗