Toomas H. Allik

High‐efficiency pyrromethene doped solid‐state dye lasers

Successful laser oscillation of various pyrromethene dyes doped in a modified acrylic plastic has been achieved. Pumped with a frequency doubled Nd:YAG laser at 532 nm, a slope efficiency of 85% has been obtained from one of the dyes in plastic, with an output beam energy of 128 mJ. A useful lifetime of greater than 20 000 shots at 3.33 Hz with output energies above 30 mJ has been demonstrated, with only a 34% loss in the available output energy.

Diode array‐pumped Er, Yb: Phosphate glass laser

A diode‐array side‐pumped Er, Yb: phosphate glass laser has been constructed. Pumped with two 970 nm, InGaAs strained‐layer diode arrays, a long pulse slope efficiency of 14% was obtained, with thresholds of 60 mJ input, a maximum output pulse energy of 20 mJ, and with output wavelengths at 1545±12 nm. When Q‐switched, the laser generated 0.3 mJ, 50 ns FWHM pulses at an output wavelength of 1533±1 nm. Visible upconversion emission in the laser rod was observed.

Tunable 7–12-µm optical parametric oscillator using a Cr,Er:YSGG laser to pump CdSe and ZnGeP 2 crystals

A CdSe optical parametric oscillator (OPO) pumped by a 2.79-mum , Cr, Er:YSGG laser yielded a 59% signal-plus-idler slope efficiency (eta), a total idler output of 1.2-2.4mJ between 8.5 and 12.3 mum , and an idler beam that was 2.2-2.5 times the diffraction limit. A ZnGeP(2) OPO operated with a lower threshold, eta = 29% , and a forward idler output of 0.7-2.4 mJ from 6.9 to 9.9 microm . The signal and idler bandwidths were typically 4 cm(-1) for each OPO.

Er:Ca5(PO4)3F saturable‐absorber Q switch for the Er:glass laser at 1.53 μm

Passive Q switching of an Er:phosphate glass laser using Er:Ca5(PO4)3F (Er:FAP) as a saturable absorber intracavity (IC) load is described for the first time. Q‐switched output was obtained consisting of a 6‐mJ single pulse of 83 ns full width at half maximum, with a 20% efficiency relative to the corresponding free‐running output in the absence of the IC Er:FAP load.

Efficient diode-array-pumped Nd:YAG and Nd:Lu:YAG lasers.

Nd:YAG (YAG) and Nd:Lu:YAG (LYAG) are investigated as high-efficiency laser materials utilizing a diode-array side-pump geometry. We demonstrate higher laser efficiencies than previously reported for transversely pumped YAG. A YAG rod yielded an optical slope efficiency of 47.7%, while a LYAG rod yielded an optical slope efficiency of 50.3%. Increased performance of these materials is attributed to higher pump absorption and lower losses.

Absorption intensities and emission cross sections of principal intermanifold and inter-stark transitions of Er3+(4f11) in polycrystalline ceramic garnet Y3Al5O12

A comparative spectroscopic study is performed on Er3+(4f11) ions doped in polycrystalline ceramic garnet Y3Al5O12 (YAG) and single-crystal laser rod, both containing nominal 50 at. % of Er3+. The standard Judd–Ofelt (JO) model is applied to the room-temperature absorption intensities of Er3+(4f11) transitions in both hosts to obtain the phenomenological intensity parameters. These parameters are subsequently used to determine the radiative decay rates, radiative lifetimes, and branching ratios of the Er3+ transitions from the upper multiplet manifolds to the corresponding lower-lying multiplet manifolds LJ2S+1 of Er3+(4f11) in these garnet hosts. The emission cross sections of the intermanifold Er3+I13∕24→I15∕24 (1.5 μm) transition as well as the principal inter-Stark transition Y1→Z4 (1550 nm) within the corresponding multiplet manifolds have been determined. The room-temperature fluorescence lifetimes of the I13∕24→I15∕24 (1.5 μm) transition in both polycrystalline ceramic and single-crystal YAG sample...

Site‐selective excitation and polarized absorption spectra of Nd3+ in Sr5(PO4)3F and Ca5(PO4)3F

Polarized absorption and fluorescence spectra were analyzed to establish individual energy (Stark) levels of Nd3+ ions in host crystals of Sr5(PO4)3F (SFAP) and Ca5(PO4)3F (FAP). Site‐selective excitation and fluorescence facilitated differentiation between Nd3+ ions in emitting sites associated with 1.06 μm stimulated emission, and nonemitting Nd3+ ions in other sites. Measurements were made on samples containing different concentrations of Nd3+ at 4 K and higher temperatures. Substitution of Nd3+ for Sr2+ or Ca2+ was accompanied by passive charge compensation during crystal growth. Crystal‐field splitting calculations were performed according to site for Stark levels of Nd3+ ions identified spectroscopically. We obtained a final set of crystal‐field parameters Bnm for Nd3+ ions in fluorescing sites with a rms. deviation of 7 cm−1 (52 levels in Nd:SFAP) and 8 cm−1 (59 levels in Nd:FAP). For one of the nonemitting sites in Nd:FAP we obtained a final set of Bnm parameters which gave a rms deviation of 6 cm...

Spectral analysis and energy-level structure of Er3+(4f11) in polycrystalline ceramic garnet Y3Al5O12

Absorption spectra obtained between 1550 and 440nm and fluorescence spectra obtained between 1700 and 1500nm are reported in a comparative spectroscopic study of polycrystalline ceramic Y3Al5O12 (YAG) and single-crystal laser rod YAG, both containing 50at.% Er3+ as a dopant in the garnet host. The spectra are observed in both samples at temperatures between 8K and room temperature. The detailed splitting of individual multiplet manifolds, LJ2S+1, Er3+(4f11), by the crystalline electric field is similar in both the ceramic sample and the single-crystal laser rod. With few exceptions, there is little shift in energy (few wave numbers) of individual Stark levels within a manifold, between dilute and concentrated Er3+ samples. This is not too surprising since Y3Al5O12 and Er3Al5O12 form a solid solution with the majority of Er3+ ions occupying cation sites having D2 symmetry in the garnet lattice over the entire solid solution range. As a check on the observed manifold splittings of Er3+ in ceramic YAG, we co...

Energy-level structure and spectral analysis of Nd3+(4f3) in polycrystalline ceramic garnet Y3Al5O12

A detailed crystal-field splitting analysis is given for the 26 lowest-energy multiplet manifolds, LJ2S+1, of Nd3+(4f3) in polycrystalline ceramic garnet Y3Al5O12 (YAG). The absorption spectra obtained between 8K and room temperature, and between 1750 and 350nm, and the fluorescence spectrum obtained at 8K and observed between 1450 and 875nm are analyzed for transitions between individual energy (Stark) levels that characterize the energy-level structure of Nd3+ ions in D2 symmetry sites, replacing Y3+ ions in the garnet host lattice. A model Hamiltonian including atomic and crystal-field terms is diagonalized within the complete 4f3SLJMJ basis set which includes 364 states. The calculated splitting of the Nd3+ energy levels by the crystal field is compared with the experimental splitting observed in both the ceramic sample and a single-crystal laser rod. Both samples have approximately the same Nd3+ concentration, about 1at.%. By varying the atomic and crystal-field parameters, we obtain a standard devia...

Tunable ultraviolet laser source based on solid-state dye laser technology and CsLiB 6 O 10 harmonic generation

Tunable UV radiation centered at 289nm was obtained from a 532-nm Nd:YAG pumped high-brightness solid-state dye laser, frequency doubled in CsLiB(6)O(10). Frequency doubling to 284-294 nm was demonstrated from a singly doped, rotating pyrromethene dye plastic disk with damage threshold >3 J/cm(2) . UV energies up to 44 mJ at 10 Hz were obtained with a 15% absolute conversion efficiency from 532 nm.