http://chglib.icp.ac.ru/subjex/2013/pdf02/ChemPhysicsLetters-2010-487(1-3)1.pdf

Quantum cascade lasers in chemical physics

The composition and properties of neodymium-doped (Nd-doped) phosphate glasses used for simultaneous high-energy (10 3 –10 6 J) and high-peak-power (10 12 –10 15 W) laser applications such as fusion energy research, are reviewed. The most common base glasses are meta-phosphates (O/P ∼3) with the approximate composition: 60P 2 O 5 –10Al 2 O 3 –30M 2 O/MO; K/Ba or K/Mg are typical modifiers. The spectroscopy of Nd 3+ in these glasses is well understood and laser properties can be accurately determined from measured spectroscopic properties. The major mechanisms for Nd 3+ non-radiative relaxation are reviewed and empirical expressions are presented that predict these effects in phosphate glasses. Optical and thermal–mechanical properties have been measured on a number of laser glasses and can be correlated with composition. Sub-critical crack growth rates in stress regions I, II and III have been reported for the first time in phosphate laser glasses. The mechanism for Pt inclusion formation and dissolution has been studied leading to damage resistant (Pt-inclusion-free) laser glasses.

Nd-doped phosphate glasses for high-energy/high-peak-power lasers

Integrated cavity output analysis of ultra-weak absorption

We have demonstrated the first stoichiometric Yb/sup 3+/ laser based on Yb/sub 3/A/sub 5/O/sub 12/ (YbAG). The laser operated in pulsed mode with a highest possible duty cycle of 85%. A slope efficiency of 27%, with respect to absorbed energy, was measured and the free-running lasing wavelength was 1048 nm for a 10% duty cycle. In a systematic analysis, measurements of spectroscopic and materials properties of (Yb/sub x/Y/sub 1-x/)/sub 3/Al/sub 5/O/sub 12/ for nominal x values of 0.05, 0.1, 0.15, 0.18, 0.25, 0.5, and 1 are reported. We also present a formalism to calculate the intrinsic fluorescence quantum efficiency (free of radiation trapping) and the fraction of reabsorbed light, based on measurements of the bulk and intrinsic emission lifetimes and the fractional thermal loading. Our best YbAG sample has an intrinsic lifetime of 0.664 ms at 94% quantum efficiency and a thermal conductivity at room temperature of 0.072 W/(cm-K).

Laser demonstration of Yb/sub 3/Al/sub 5/O/sub 12/ (YbAG) and materials properties of highly doped Yb:YAG

Absorption spectroscopy in high-finesse cavities for atmospheric studies

Radiometrically calibrated spectroscopic techniques employing an integrating-sphere detection system have been used to determine the fluorescence quantum efficiencies for two commercially available Nd3+-doped phosphate laser glasses, LG-750 and LG-760. Quantum efficiencies and fluorescence lifetimes were measured for samples with various neodymium concentrations. It is shown that the effects of concentration quenching are accurately described when both resonant nonradiative excitation hopping (the Burshtein model) and annihilation by cross relaxation are accounted for by Forster–Dexter dipole–dipole energy-transfer theory. The Forster–Dexter critical range for nonradiative excitation hopping was found to be RDD = 11 A, while the critical range for cross relaxation was close to RDA = 4 A in these glasses. The quantum efficiency at low Nd3+ concentrations was (92 ± 5)%, implying a nonradiative relaxation rate of 210 ± 150 s−1 for isolated ions. Improved values for the radiative lifetimes and the stimulated emission cross sections for these glasses were also deduced from the measurements.

Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses

The design and operation of an absorption spectrometer is described. The spectrometer isused to measure water vapor absorption in the ambient laboratory atmosphere.(AIP)

High sensitivity atmospheric transmission measurements using a cavity ringdown technique.

Laser pumped laser experiments1 on Na3Ga2Li3F12:Cr3+ indicated levels of gain 3 to 4 times lower than theoretical prediction. The value of the emission cross section used in the prediction was based on the assumption of unity quantum efficiency at room temperature. The reduced gain could then be indicative of a high nonradiative relaxation rate (i.e., nonunity quantum efficiency) and/or the presence of excited state absorption. The present study yielded a value of nf = .92±.06 indicating that the discrepancy between the theoretical and measured gain cannot be explained by a low quantum efficiency.

A. J. Ramponi

Papers

Quantum efficiency and excited-state relaxation dynamics in neodymium-doped phosphate laser glasses

High sensitivity atmospheric transmission measurements using a cavity ringdown technique.

Measurement of the Luminescence Quantum Efficiency of Na3Ga2Li3F12:Cr3+ by Laser Calorimetry