Cooperative multi-ion energy transfer and two-step excitation processes have been used to achieve population inversion and laser action in erbium-doped YLiF4 and BaY2F8. Pulsed and cw experiments have been carried out to provide details of the pumping pathways and to identify systems having particularly favorable values for the upconversion transfer coefficient. Examples of laser emission at four wavelengths shorter than the cw pump will be described for YLiF4. Pulsed IR laser output has been demonstrated in BaY2F8:Er, where the time dependence confirms efficient cooperative energy transfer associated with the 4I13/2 level. Spectroscopic and kinetic data are reported.
Abstract : Research concerning molecular and chemical lasers was conducted in the following areas: (1) Vibrational relaxation measurements at T=300 K of HF(v=1),DF(v=1), CO2(001); (2) Collisional deactivation of CO(v=1) by oxygen atoms over the temperature range 273K to 390K; (3) Vibrational relaxation measurements in the HF-DF, HF-CO2 and DF-CO2 systems at very low temperatures; (4) Studies directed toward the measurement of the V to R rates of energy transfer in HF - HF collisions; (5) Studies directed towards the rapid generation of electronically and/or vibrationally excited boron containing di and triatomics; (6) Reaction rate studies between B, BH, BH2 or BH3 radicals with oxidizers such as NF3, N2O and NO2; and (7) Homogeneous initiation of chemical reactions by pulsed laser heating.
We have obtained coherent operation of multiple pulsed dye oscillators by using a single phase conjugate mirror as a common end mirror for up to three physically distinct cavities. The phase conjugate mirror operates via the photorefractive effect in a crystal of BaTiO3, through a four-wave mixing process that requires no external pumping beams. The system has been operated in both a narrow-band (0.05 nm) and a broadband (0.25 nm) configuration.
The dimer compounds ${\mathrm{Cs}}_{3}$${\mathrm{Er}}_{2}$${\mathit{X}}_{9}$ (X=Cl,Br,I) were synthesized and grown as crystals. Their f-f absorption spectra were measured and their upconversion luminescence behavior was studied as a function of temperature. Both $^{4}$${\mathit{I}}_{15/2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{I}}_{11/2}$ and $^{4}$${\mathit{I}}_{15/2}$${\ensuremath{\rightarrow}}^{4}$${\mathit{I}}_{9/2}$ excitations were used. The highest-energy phonons were found by Raman spectroscopy at 285, 190, and 160 ${\mathrm{cm}}^{\mathrm{\ensuremath{-}}1}$ in ${\mathrm{Cs}}_{3}$${\mathrm{Er}}_{2}$${\mathit{X}}_{9}$ (X=Cl,Br,I), respectively. The upconversion and cross-relaxation behavior is essentially determined by two factors: (i) As a result of the lower phonon energies multiphonon-relaxation processes are orders of magnitude less competitive than in fluorides; (ii) as a result of their dimeric character with very short intradimer ${\mathrm{Er}}^{3+}$-${\mathrm{Er}}^{3+}$ distances and the relatively short interdimer separations all types of nonradiative energy-transfer processes are very competitive. The following trends were observed: a redshift of the f-f multiplet baricenters of up to 1% between chloride and iodide, a reduction of crystal-field splittings up to 50% between chloride and iodide, enhanced near-infrared to visible upconversion efficiency between chloride and bromide or iodide. All these trends are rationalized with simple models. For some selected crystal-field transitions energy splittings resulting from exchange interactions within the dimers were observed.
We have obtained coherent operation of multiple pulsed dye oscillators by using a single phase conjugate mirror (PCM) as a common end mirror for up to three physically distinct cavities. The PCM operates via the photorefractive effect in a crystal of BaTiO3, through a four-wave mixing process which requires no external pumping beams. The system has been operated in both a narrow band (0.05 nm) and a broadband (0.25 nm) configuration.
The rate constants for the collisional relaxation of vibrationally excited CO2(0001) and CO(v=1) molecules by molecular bromine have been determined by the laser induced fluorescence technique. The measured rates were kCO2–Br2 =246±23 s−1 torr−1 and kCO–Br2 =6.34±0.5 s−1 torr−1. The relevance of these rates to E→V transfer lasers is discussed.
Two measurements were performed of the fast initial fluorescence decay of the 4F3/2 state of Nd3+, following pulsed excitation of the ion in two garnet crystals, (i) Nd(1%), Er(15%), Cr(1%):YAG and (ii) Nd(1.5%), Er(20%):YSGG. The nature of the interaction between Nd3+ and Er3+ ions is analyzed with a Monte Carlo model for the nonradiative energy transfer from Nd to Er. Our measurements and the Monte Carlo analysis corroborate the presence of a submicrosecond fluorescence decay transient and the reported nature of the interaction that drives the energy transfer, i.e., a mixture of electrostatic interactions (dipole–dipole, dipole–quadrupole, and quadrupole–quadrupole) and an exchange interaction.
The rate constants for the collisional relaxation of vibrationally excited CO2 (00°1) and CO (v=1) molecules by some perfluoroalkyl bromide and iodide molecules have been determined by the laser induced fluorescence technique. The measured rates were kCO2–CF3Br=1.47±0.05×105 s−1⋅torr−1, kCO2–C2F5Br=1.67±0.05 s−1⋅torr−1, kCO2–CF3I=2.69±0.08×105 s−1⋅torr−1, kCO2–C2F5I=0.99±0.04×105 s−1⋅torr−1, kCO2–n–C3F7I=1.16±0.07×105 s−1⋅torr−1, and kCO–CF3Br=819±39 s−1⋅torr−1. The relevance of these rates to E→V transfer lasers is discussed. A new and very liable determination of the self-relaxation rate constant of pure CO2 has also been determined: this rate is kCO2–CO2=305±6 s−1⋅torr−1.
Control and optimization of the behavior of photorefractive crystals requires first, a thorough understanding of the nature (charge state, local symmetry, and electronic structure) of the defects/impurities present in these materials, and of their interaction with light. 1,2,3 Toward this end, we have carried out electron paramagnetic resonance (EPR), photo-EPR, and optical absorption measurements on a variety of BaTiO 3 samples doped with transition metal ions. These crystals were grown by top-seeded solution growth from a melt with an excess of TiO 2 .
