arXiv subjects

Alexander R. Albrecht

Publications and source records attributed to Alexander R. Albrecht.

5 recordsLinked to original sources

arXiv2025

Solid-state Laser Cooling

Since the first proof-of-concept demonstrations of photoluminescence-based optical refrigeration, solid-state laser cooling has developed into a credible competitor to conventional cryogenic technologies. Solid-state laser cooling continues to advance as new materials push cooling limits. These developments have created a need to consolidate progress made to date as well as standardize critical experimental considerations needed for reliable and verifiable cooling measurements. This primer therefore outlines essential concepts and requirements, which underpin solid-state laser cooling. The primer summarizes key milestones achieved with cooling-grade, rare-earth-doped glasses and crystals as well as with semiconductors. It additionally highlights emerging applications of solid-state optical refrigeration. To strengthen the consistency and reproducibility of cooling results going forward, two reporting checklists are introduced. They cover materials, cooling metrics, and thermometry. This primer is intended to serve as both a tutorial and a practical reference for incoming and existing researchers involved in solid-state laser-cooling.

physics.optics↗

arXiv2025

Thermal imaging by utilization of CsPbBr3 quantum dot photoluminescence

The temperature-dependent photoluminescence of perovskite quantum dots (CsPbBr3) in the visible band, is analyzed to evaluate their suitability for use in thermometry. A differential measurement of the photoluminescence can be used to estimate the surface temperature. Thermal imaging is demonstrated by using the Bayer-pattern of a cost-effective consumer-grade digital camera to determine the spectral shift. The temperature change of traces on a printed circuit board are visualized as proof of principle. This technique promises a novel approach for thermal imaging of arbitrary samples with optical resolution (wavelength of ~ 500 nm), instead of typical black-body wavelengths (~ 10 micrometer). Premature degradation of the quantum dots has been mitigated by embedding them in a poly-methyl methacrylate (PMMA) film, which can then be applied to arbitrary surfaces.

physics.optics↗

arXiv2021

Laser Cooling of a Yb Doped Silica Fiber by 18 Kelvin From Room Temperature

A ytterbium doped silica optical fiber has been cooled by 18.4K below ambient temperature by pumping with 20W of 1035nm light in vacuum. In air, cooling by 3.6K below ambient was observed with the same 20W pump. The temperatures were measured with a thermal imaging camera and differential luminescence thermometry. The cooling efficiency is calculated to be 1.2+-0.1%. The core of the fiber was codoped with Al3+ for an Al to Yb ratio of 6:1, to allow for a larger Yb concentration and enhanced laser cooling.

physics.optics↗

arXiv2020

Laser-induced anti-Stokes fluorescence cooling of ytterbium-doped silica glass by more than 6 Kelvin

Laser cooling of a solid is achieved when a coherent laser illuminates the material, and the heat is extracted by resulting anti-Stokes fluorescence. Over the past year, net solid-state laser cooling was successfully demonstrated for the first time in Yb-doped silica glass in both bulk samples and fibers. Here, we improve the previously published results by one order of magnitude and report more than 6K of cooling below the ambient temperature. This result is the lowest temperature achieved in solid-state laser cooling of silica glass to date to the best of our knowledge. We present details on the experiment performed using a 20W laser operating at 1035nm wavelength and temperature measurements using both a thermal camera and the differential luminescence thermometry technique.

physics.optics↗

arXiv2019

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

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.

physics.optics↗