Ralph R. Jacobs

Dependence of the 4 F 3/2 → 4 I 11/2 induced-emission cross section for Nd 3+ on glass composition

Systematic studies of spectral intensities using the Judd-Ofelt (J-O) theory for crystal-field-induced electric-dipole transitions demonstrate that Nd-doped glasses can be tailored for specific laser applications by proper selection of the glass constituents. Variations with glass composition are reported for the following properties: induced-emission cross section, peak fluorescence wavelength, effective fluorescence bandwidth, radiative lifetime, transition probabilities, and fluorescence branching ratios. Both glass network formers and network-modifier ions were changed. In these studies the induced-emission cross section for the Nd3+,4 F_{3/2} \rightarrow 4 I_{11/2} laser transition was varied by more than a factor of 4 by changing the glass host.

Measurement of excited‐state‐absorption loss for Ce3+ in Y3Al5O12 and implications for tunable 5d→4f rare‐earth lasers

Broad bandwidth 5d→4f transitions in Ce3+ have been considered for tunable laser action. In this letter, optical probe measurements of excited Ce3+ ions in Y3Al5O12 show that stimulated emission in the 550–610‐nm region is not possible at 295 K because of excited‐state absorption. Transient measurements demonstrate that part of this loss has ≈75‐ns lifetime and is associated with absorption from the lowest 5d level; a longer‐lifetime loss is also observed. The excited‐state‐absorption loss is reduced at lower temperatures.

Rotational relaxation rate constants for CO2

Rotational relaxation rate constants, krot, have been measured for the CO2 00°1 level in three kinds of amplifiers: one using CO2 alone and two others using mixtures of CO2–He and CO2–N2. The experiment consists of perturbing the CO2 00°1 level with a ∼2‐nsec saturating pulse at P(20) in the 10.4‐μ band and monitoring the subsequent repopulation of the J = 19 rotational state with a probe beam set at P(20) in the 9.4‐μ band. The determined rate constants are kCO2–CO2 = 1.3±0.2, kCO2–He = 0.6±0.1, and kCO2–N2 = 1.2±0.2, all in units of 107 sec−1 Torr−1.

Laser generation from 6 to 35 μm following two‐photon excitation of ammonia

Laser action has been observed for the first time in ammonia subsequent to two‐photon absorption. Oscillation has been demonstrated in 14NH3 following two‐photon excitation by a pair of CO2 TEA lasers operating on the P (34) and P (18) lines in the 10.4‐μm band, respectively. The observed wavelengths are 6.27, 6.69, 12.11, 13.72, 15.88, 15.95, 18.92, 19.55, 26.10, and 35.50 μm. Identification with existing spectroscopic information indicates that eight of the laser transitions occur within the ν2 manifold and originate by radiative pathways from the 2ν2−(5,4) level at 2115.88 cm−1, whereas the remaining two, at 6.27 and 6.69 μm, take place in the ν4 mode. The usefulness of employing such lasers as sensitive probes for molecular collisional processes in excited vibrational levels is indicated.

Optical gain at 1.06 μm in the neodymium chloride‐aluminum chloride vapor complex

First observation of optical gain for trivalent rare‐earth molecular vapors is reported. Specifically, gain coefficients a few tenths percent/cm have been measured in the neodymium chloride—aluminum chloride vapor complex at 1.06 μm for the Nd3+ : 4F3/2→4I11/2 transition. The corresponding stored energy density at this wavelength is ≈35 J/l. The observed inversion lifetime of ≳10 μsec is interpreted to be dominated by near‐resonant excited‐state–excited‐state binary collisions. Use of trivalent rare‐earth molecular vapors as gain media in fusion laser amplifiers is discussed.

Deactivation on the Nd3+, 4F32 level in neodymium chloride - aluminum chloride vapor complexes

Abstract The first fluorescence lifetime studies in a trivalent rare earth-metal vapor complex NdCl 3 · (AlCl 3 ) χ are reported. The observed, temperature-dependent, nonradiative deactivation and the inferred radiative lifetime are discussed in terms of various models. At 803 K, corresponding to a density of 4.6 × 10 17 Nd 3+ ions/cm 3 and a total system pressure ≈5 atm, the measured lifetime is 46 μs.

Nonradiative intramolecular deactivation of Tb3+ fluorescence in a vapor phase terbium(III) complex

Abstract For the first time, fluorescence lifetime studies are reported for a trivalent rare-earth gas: specifically, for the 5 D 4 state of Tb 3+ in the vapor phase chelate 2,2,6,6-tetramethyl-3,5-heptanedione. Measurements of the fluorescence decay as a function of temperature and pressure demonstrate that intermolecular collisional deactivation is unimportant and that nonradiative deactivation by intramolecular processes dominates the fluorescence lifetime at temperatures of 230–300°C. The rate for the latter processes is well described by an Arrhenius equation and suggests that the Tb 3+ relaxation occurs via transfer to low-lying excited states of the chelate.

Ce3+→Nd3+ energy transfer in silicate glass

Radiative and nonradiative energy transfer from optically excited Ce3+ to Nd3+ has been studied in silicate laser glass. The quantum efficiency for nonradiative Ce3+→Nd3+ transfer was determined from the Ce3+ fluorescence decay rates. The Ce3+ fluorescence decayed exponentially with a rate proportional to the Nd3+ concentration. Physical processes to account for the observed energy transfer are discussed. In addition, the utility of Ce3+→Nd3+ energy transfer is considered for laser applications. In this context, the energy deposited in a Ce3+‐Nd3+–codoped glass was calculated using a computer program containing a model of the xenon flashlamp spectrum as a function of current density. The results indicate that improvements in the optical pumping efficiency in typical Nd lasers are limited to <40%.

Induced-emission cross sections for the 4 F 3/2 &#8594; 4 I 13/2 transition in neodymium laser glasses

Induced-emission cross sections for the4 F_{3/2} \rightarrow 4 I_{13/2} transition of Nd3+in several commercial and experimental laser glasses have been determined using spectroscopic data and the Judd-Ofelt treatment of electric-dipole transition probabilities.

High‐efficiency energy extraction in backward‐wave Raman scattering

Pump depletions of 70–75% have been demonstrated for a KrF‐laser‐driven, methane‐gas‐filled backward Raman amplifier and are in agreement with predictions of the Frantz‐Nodvik saturated‐amplifier model. The associated counterpropagating Stokes laser intensity is determined to be ≳3.5 times that of the pump; the corresponding pulse compression ratio is ≈5.