Solid-state laser cooling in Yb:CaF₂ and Yb:SrF₂ by anti-Stokes fluorescence

Abstract

We report on the first example, to the best of our knowledge, of solid-state laser cooling in ytterbium-doped CaF2 and SrF2 crystals by anti-Stokes fluorescence. The crystals were grown by the Czochralski method in a fluorine-rich atmosphere to prevent the formation of divalent ytterbium ions. Using laser-induced thermal modulation spectroscopy (LITMoS), we find the cooling efficiencies for both crystals to be higher than 3% at room temperature. According to model calculations performed using temperature-dependent spectroscopic data, these crystals can be cooled to temperatures as low as 150 K when excited at around 1030 nm.

Exploring the extent to which optical refrigeration can enable high precision accelerometry using optical levitation

“…Because the temperatures at which micro-scale samples would vaporize in vacuum are largely unavailable in the literature, and because bulk CaF 2 has a lower melting point at STP than silica, we use 1360 K as what may be an overestimate of the temperature at which vaporization of optically trapped CaF 2 particles would occur. This hypothetical particle allows us to combine the reported optical refrigeration properties of Yb:CaF 2 42 with the background absorption coefficients measured in real, levitated optomechanical sensors that are limited by vaporization. 7,28 While this hypothetical particle is does not represent any one, real system, we can use this model to understand the extent to which optical refrigeration mitigates difficulties with vaporization due to background absorption.…”

“…Optical refrigeration is modeled using resonant absorption coefficients of Yb:CaF 2 at 1034 nm published by Püschel et al 42 and provided to us by Prof. Hiroki Tanaka's research group. We double those coefficients to model a 10% Ytterbium doping concentration versus the 5% concentration used by Tanaka's group.…”

“…γ is assumed to be 0.5 to describe inhomogeneous broadening. 42,75 To estimate the saturation intensity, we use…”

Fluorescent contactless method for temperature determination of YAl3(BO3)4 crystals doped with Yb3+ ions

“…Contactless approaches to temperature measurement have been applied to laser gain media, such as YLF [7,8,10], YAG [9,11], KYW [11], CaF2 [12], SrF2 [12], ZBLAN [6]. However, up to our knowledge, there is no research dedicated to the investigation of temperature dependent fluorescence of novel prospective media based on YAB crystals.…”

Accurate Characterization of the Properties of the Rare-Earth-Doped Crystal for Laser Cooling

“…Since then, researchers have focused on exploring new promising potential materials for cryogenic optical cooling. So far, net cooling by laser has been demonstrated not only in a variety of rare-earth-doped (Yb 3+ -, Tm 3+ -, Er 3+ -and Ho 3+ -) bulk and nano crystals [2,[15][16][17][18][19][20][21][22][23][24][25][26][27][28][29][30][31], but also in glassy materials [32][33][34] and semiconductors of nano structure [35][36][37]. Among all the crystals tested, fluoride crystals have exhibited the best cooling performances [38][39][40].…”