Enhanced efficiency ultraviolet LiYXLu1 - XF4:RE3+ (RE = Ce,Yb) laser

© 2014 Astro Ltd. We report the results of laser tests in LiYXLu1 - XF4:RE3+ (RE = Ce, Yb; x = 0, 0.3) crystals and the effect on laser characteristics (slope efficiency and tuning range) of such variations of the lasing conditions as the pumping repetition rate, temperature and additional illumination of the active element. It was established that slope efficiency increases and the tuning range of ultraviolet lasing widens and becomes continuous when the crystal is cooled down below 0 °C, or exposed to 532 nm radiation. 266 and 340 nm illumination reduces or completely quenches laser oscillation. The photodynamic processes underlying these effects, such as excited-state absorption and formation/destruction of color centers, are discussed

Optical vector network analysis of ultra-narrow transitions in 166^{166}Er3+^{3+}:7^7LiYF4_4

We present optical vector network analysis (OVNA) of an isotopically purified $^{166}$Er$^{3+}$:$^7$LiYF$_4$ crystal. The OVNA method is based on generation and detection of modulated optical sideband by using a radio-frequency vector network analyzer. This technique is widely used in the field of microwave photonics for the characterization of optical responses of optical devices such as filters and high-Q resonators. However, dense solid-state atomic ensembles induce a large phase shift on one of the optical sidebands which results in the appearance of extra features on the measured transmission response. We present a simple theoretical model which accurately describes the observed spectra and helps to reconstruct the absorption profile of a solid-state atomic ensemble as well as corresponding change of the refractive index in the vicinity of atomic resonances.Comment: 4 pages, 5 figure

Two-step photoconductivity in LiY<inf>x</inf>Lu<inf>1 – x</inf>F<inf>4</inf>:Ce,Yb crystals

© 2016, Pleiades Publishing, Ltd.Photoconductivity of LiYxLu1–xF4:Ce,Yb (x = 0–1) crystals is measured under one- and two-step excitation. It is established that the photoconductivity is due to intra-center transitions from excited states of Ce3+ ions. The position of the ground 4 f-state of Ce3+ ion relative to the bottom of the conduction band is determined. The choice of pumping conditions to obtain the lasing on the 5d–4f transitions of trivalent cerium in these active media is substantiated

Investigation of gain characteristics in mixed crystals LiMeF4 (Me = Y, Lu, Yb) doped by Ce3+ ions

Differential gain spectra in the range 295-335 nm were measured in crystals of scheelite structure LiY1 - x Lu x F4 (x = 0-1), doped by Ce3+ ions. It is shown that variation of Lu 3+ and Y3+ ions relative content in LiY1 - x Lu x F4 crystals allows to manipulate the spectral width of the amplification band. Cross-sections of excited-state absorption at the wavelengths of Ce3+ luminescence, probability ratios of formation and thermal destruction of color centers depending on the Y3+ ions content in LiY1 - x Lu x F4 crystals were estimated. Even better gain characteristics have been demonstrated by LiLuF 4:Ce3+, doped by Yb3+ ions. The highest optical gain coefficient with a wide amplification band among studied samples was observed in LiLuF4:Ce3+ crystal, codoped by Yb 3+ ions. © 2014 Pleiades Publishing, Ltd

Strongly anisotropic magnetocaloric effect in a dipolar magnet LiGdF4_4

We report the detailed study of the magnetocaloric effect (MCE) in a dipolar-Heisenberg magnet LiGdF$_4$ using magnetization measurements performed on a single crystal sample. Entropy variation on isothermal demagnetization from the magnetic field up to 3 T is determined in the temperature range 2-10 K for two principal directions of the applied field (parallel and perpendicular to the tetragonal $c$-axis of the crystal). The MCE is found to be highly anisotropic, with the cooling efficiency being up to twice higher at $H\parallel c$. The results are nicely interpreted in the frame of a conventional molecular field approach taking into account considerable anisotropy of the paramagnetic Curie-Weiss temperature. These results are compared to earlier studies of MCE in powder samples of LiGdF$_4$ [T. Numazawa et al., AIP Conf. Proc. 850, 1579 (2006)] as well as with analogous data for other well known magnetocaloric materials. Our findings may open new possibilities to enhance the efficiency of magnetic refrigeration in the liquid helium-4 temperature range.Comment: 4 pages, 3 figure

Superhyperfine structure of the ESR spectra of Gd³⁺ impurity ions in LiYF<inf>4</inf> double fluoride

© 2017, Pleiades Publishing, Ltd.Electron spin resonance spectra of Gd3+ ions forming a small (~0.0001 at %) impurity in a LiYF4 single crystal have been investigated in a wide temperature range from liquid helium to room temperature. A number of the fine-structure components of the spectrum exhibit a pronounced superhyperfine structure depending on the orientation of the external magnetic field with respect to the crystallographic axes. The superhyperfine structure was not observed in earlier ESR studies of double fluorides with a Gd3+ impurity

Photodynamic processes and laser performance of Ce, Yb: LiYXLu1-XF4 mixed crystals

Photodynamic processes and temperature dependencies of lasing in Ce+Yb:LYLF mixed crystals are investigated. The mechanisms leading to the observed phenomena and allowing control on the optical qualities of the active media are discussed. © OSA 2013

Laser performance investigation of a new UV active media LiY 0,3Lu0,7F4:Ce3+ and LiY 0,3Lu0,7F4:Ce3++Yb3+

We show that the LiY0,3Lu0,7F4:Ce 3+ and LiY0,3Lu0,7F4:Ce 3++Yb3+ crystals are promising active media of UV spectral range with low-threshold lasing (30-90 mJ/cm2). Due to crystal-chemical approach (additional doping by ions Yb3+) we obtained the effect of suppression of spurious photodynamic processes. The active medium LiY0,3Lu0,7F4: Ce3++ Yb3+ combines properties of saturable amplifier and oscillator with small saturation energy, and promising to generate pulses of ultrashort duration in the UV spectrum. © Published under licence by IOP Publishing Ltd

Spectral-kinetic studies of SrAlF 5 doped by trivalent rare-earth ions

Photochemical properties of Ce 3:SrAlF 5 and Ce 3,Yb 3:SrAlF 5 single crystals together with spectroscopic and kinetic characteristics of several optically nonequivalent impurity centers and energy transfer between them are described. It is shown that co-activation by Yb 3 ions effectively suppresses color centers in Ce,Yb:SAF crystals. It was found out that in Ce,Yb:SAF crystals Yb ions exist simultaneously in 2 and 3 valent state. Three types of optically nonequivalent luminescent centers corresponding to the doublets in luminescence spectrum centered at 290, 305 and 370 nm (Ce I, Ce II, Ce III, respectively) have been observed. Analysis of luminescence spectra and decays leads to the conclusion that there is no energy transfer between either cerium centers or from Ce 3 to Yb 2 apart from the Ce III center which luminescence is slightly quenched by Yb 2. © 2012 Elsevier B.V. All rights reserved