Improving laser cooling efficiencies of Yb-doped yttrium aluminum garnet by utilizing non-resonant anti-Stokes emission at high temperatures

Abstract

Laser cooling in solids has been demonstrated, and cooling from room temperature to cryogenic temperatures has so far been the main focus of research. However, operation at high temperatures can be advantageous. We propose that laser cooling of Yb-doped yttrium aluminum garnet ceramic discs is enhanced above 300 K. Photoluminescence (PL) spectra is evidence that the phonon-assisted energy transfer from resonant states, which exhibit a narrow PL peak, to inhomogeneously distributed energy states becomes stronger at higher temperatures. This results in an enhanced non-resonant anti-Stokes PL at high temperatures. The ideal cooling efficiency determined from the PL spectrum at 470 K is 1.7 times higher than that at 300 K.

An energy transfer accompanied by phonon absorption in ytterbium-doped yttrium aluminum perovskite for optical refrigeration

“…3(a) and the literature. 25 The difference of two excitation conditions does not affect our conclusion.…”

“…23,24 In addition, based on PL measurements, we reported that the ideal cooling efficiencies of Yb-doped YAG and Er-doped YAG are improved at high temperatures (above 300 K) due to an enhanced inhomogeneous anti-Stokes PL contribution. 25,26 An important result is that this "non-resonant" anti-Stokes PL showing the broadly distributed emission is the emission from RE ions surrounded by an inhomogeneous alloy structure. Here, the resonant anti-Stokes PL is defined as the emission originated by the intra-orbital f-f transitions between the ideal energy states of RE ions in host crystal, which shows narrow PL peaks.…”

Yb-doped Y–Al–O thin films with a self-organized columnar structure and their anti-Stokes photoluminescence properties

“…30 The energy transfer from M(D) to other sites has been observed in Yb:YAM single crystals, 30 and our previous experimental results for Yb:YAP and Yb:YAG suggest that energy transfer processes play a key role in solid-state laser cooling at high temperatures. 19,32…”

Adaptive four-level modeling of laser cooling of solids

“…( 6) and the relative operating bandwidth of the pumping frequency. Therefore, previous efforts in enhancing η c such as operating at higher temperature 15 or exploring rare-earth ions of lower transition frequencies (e.g. compared to Yb 3+ that operates at ∼ 1 µm, Tm 3+ is at ∼ 2 µm) can also be applied to increase the operating bandwidth.…”

“…1 (b), the absorption spectrum in the cooling regime (red) tends to follow a smooth exponential decay features, known as the cooling tail or the long-wavelength tail 13 . A simple laser cooling model developed in this domain can be beneficial for applications at room-temperature or above 15 , such as cooling of light-driven spacecraft 16,17 and high-power lasers where heat needs to be dissipated efficiently 8,[18][19][20] .…”