Mikhail A. Noginov

Study of luminescence concentration quenching and energy transfer upconversion in Nd-doped LaSc 3 (BO 3 ) 4 and GdVO 4 laser crystals

Luminescence concentration quenching and upconversion have been quantitatively investigated in neodymium-doped LaSc3(BO3)4 (LSB) and GdVO4 (GVO) laser crystals. The microparameter of cross relaxation (self-quenching) was determined in Nd:GVO as 3.6×10-40xa0cm6/s. It is shown that, in Nd:LSB, upconversion is static, with the upconversion microparameter Cda=(0.5–1.1)×10-37xa0cm6/s. In Nd:GVO, upconversion is migration accelerated, with the upconversion macroparameter α≈1.2×10-15xa0cm3/s. The influence of upconversion on laser operation is discussed.

Line narrowing in the dye solution with scattering centers

Abstract As was shown by Markushev et al. [1], laser-like emission without cavity can be obtained from a scattering gain medium, such as powder of Nd doped laser crystals. In the recent work by Lawandy et al. [2] a close phenomenon was observed in a concentrated rhodamine 640 dye solution in the presence of scatterers. The work in Ref. [2] is the first where gain and scattering are separate. In this case lasing evidently is not initiated within the particles, in contrast to the Markushev et al. case, where the gain is in the particles, which supports morphology-dependent resonances. The work by Sha et al. [3] showed similar results in concentrated dye, but it also showed that introduction of a low density of scatterers raises the threshold required for the laser-like effects in the low-concentrated dye. We carried out our own experiments in rhodamine 6G laser dye and observed the laser-like effects both in dilute and concentrated dye with and without scatterers. In our experiment the wavelength of stimulated emission was strongly dependent on the scatterers concentration. Our observations and some results of Refs. [2,3] are explained with a simple ASE (amplified spontaneous emission) model.

Short-pulsed stimulated emission in the powders of NdAl 3 (BO 3 ) 4 , NdSc 3 (BO 3 ) 4 , and Nd:Sr 5 (PO 4 ) 3 F laser crystals

Short (>300-ps) pulses of stimulated emission were found from powders of NdAl3(BO3)4, NdSc3(BO3)4, and Nd:Sr5(PO4)3F laser crystals during 532- and 805-nm excitation. Study of stimulated emission in the mixture of two powders has shown that the different components influence each other. That implies a collective behavior of emitting particles. The main features of experimentally observed stimulated emission are described with a simple model accounting for 4F3/2 excited-state concentration and emission energy density. The threshold of stimulated emission in powders is shown to be inversely proportional to the small-signal amplification along the photon path in the pumped volume.

Optical characterization of Mn:YAlO 3 : material for holographic recording and data storage

Photoinduced coloration and the holographic grating recording associated with it are experimentally studied in Mn-doped yttrium orthoaluminate (Mn:YAlO3). High diffraction efficiency is demonstrated in visible and in infrared light. The diffraction efficiency at 514.5 nm exceeds 50%. The strong energy exchange between the writing beams observed in a two-wave mixing experiment suggests that diffraction in Mn:YAlO3 is due to mainly nonlocal holographic effect and an electro-optical effect. Mn:YAlO3 is shown to be a promising material for holographic recording and optical storage.

Excitation scheme for the upper energy levels in a Tm:Yb:BaY 2 F 8 laser crystal

Energy-transfer processes (including upconversion) are quantitatively studied in a Tm:Yb:BaY2F8 laser crystal. Several energy-transfer, cross-relaxation, and upconversion parameters are determined. We prove that at excitation of the crystal via Yb ions, the Tm levels xa03F4,xa03H4,xa03F3,2,xa01G4, and xa03P0 are populated via Yb–Tm interaction, and the level xa01D2 is likely populated owing to xa03F3xa0Tm–3F3xa0Tm upconversion. The possibility of resonant excited-state absorption at 706 nm and resonant energy-transfer upconversion populating the level xa01D2 are discussed. The possibility of avalanche pumping of Tm:Yb:BaY2F8 at 706 nm is shown.

Two-step upconversion luminescence in Yb:Tb:YSGG crystal

Multiline upconversion luminescence ranging from 375 to 635 nm was studied in Yb:Tb:YSGG crystal, a possible candidate for a tunable upconversion laser material. This luminescence was attributed to the transitions starting from the 5D3 and 5D4 excited levels of Tb. Two sequential steps in the upconversion were determined: at the first step Yb–Tb cooperative upconversion and cooperative absorption populate level 5D4, and at the second step interaction of excited Yb and Tb (in the 5D4 state) ions populates level 5D3. At 500-mW Ti:sapphire pumping, the excited-state concentration of Tb ions exceeded 2% of Yb excited-state concentration.

REABSORPTION TRAPPING OF LUMINESCENCE IN LASER CRYSTALS : ENHANCEMENT OF ENERGY STORAGE AND UPCONVERSION

It is shown that reabsorption of luminescence in laser crystals can enhance energy storage, energy transfer, and upconversion in solid-state laser media. These effects, experimentally observed in Yb-doped and Er-doped crystals, can potentially decrease the threshold for compact cw pumped lasers. The influence of parasitic laser modes and the amplification of spontaneous emission on population inversion in reflective coated laser elements is discussed.

Diffusion and pseudo-phase-conjugation effects in coherent backscattering from Nd0.5La0.5Al3(BO3)4 ceramic

Abstract We study coherent backscattering in Nd 0.5 La 0.5 Al 3 (BO 3 ) 4 ceramic and demonstrate what we call the effect of pseudo phase conjugation from scattering medium. We show that coherent backscattering can correct for large-scale distortions of the light wave front. The imperfections in the backscattering imaging as well the impossibility of correcting for small-scale wave front distortions are discussed. An `optical equivalent circuit of known components which give the same behavior as a scattering medium is offered.

Holographic current study in laser and photorefractive crystals

Summary form only given. We generalized the theory behind the light-induced grating (LIG) electro-motive force (EMF) technique for material characterization and interferometry, first introduced by Petrov et al. In particular, we have accounted for the screening length, that allowed us to describe adequately the dependence of the amplitude, and the decay-time.

Study of photoconductivity and holographic current in rare-earth-doped Y 3 Sc 2 Ga 3 O 12 laser crystals

The photoconductivity and holographic current have been studied in Er-, Tm-, and Ho-doped Y3Sc2Ga3O12 laser crystals under visible and infrared excitation. Kinetics and spectroscopic studies have shown that photoconductivity is linearly proportional to the concentration of excited 4f states. The holographic current was described with a model accounting for the energy transfer between the rare-earth and ligand electronic shells, ionization, recombination, and the diffusion and drift currents in the conduction band. The dependence of the holographic current on the modulation frequency, grating vector, etc. were used to determine the carriers’ diffusion length and the screening length in Er-doped crystals.