# Tm-doped Crystals for mid-IR Optical Cryocoolers and Radiation Balanced Lasers

## TL;DR

This paper presents the first demonstration of optical refrigeration in Tm:YLF crystals, detailed spectroscopic analysis, and discusses their potential for mid-IR cryocoolers and radiation balanced lasers in the eye-safe spectrum.

## Contribution

It provides comprehensive characterization of Tm-doped crystals, including the first optical refrigeration demonstration in Tm:YLF, and explores their application in mid-IR cryocoolers and lasers.

## Key findings

- Room temperature laser cooling efficiencies of 1-2%.
- Estimated minimum achievable temperatures of 110-160 K.
- Proposal of a 2-tone RBL using Tm:YLF and Ho:YLF.

## Abstract

We report the complete characterization of various cooling grade Tm-doped crystals including the first demonstration of optical refrigeration in Tm:YLF crystals. Room temperature laser cooling efficiencies of 1% and 2% (mol) Tm:YLF, and 1% Tm:BYF crystals at different excitation polarizations are measured and their external quantum efficiency and background absorption are extracted. By performing detailed low-temperature spectroscopic analysis of the samples, global minimum achievable temperatures of 160 K to 110 K are estimated. The potential of Tm-doped crystals to realize mid-IR optical cryocoolers and radiation balanced lasers (RBLs) in the eye-safe region of the spectrum is discussed, and a promising 2-tone RBL in a tandem structure of Tm:YLF and Ho:YLF crystals is proposed.

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Source: https://tomesphere.com/paper/1901.07737