Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Log inSign up
Challenges
Datasets
Workspaces
Papers
Discussions
Leaderboard
Blog
Job Board
Q3AS

© 2026 Aqora Quantum S.A.S.

TermsPrivacyLegal Notice

Journal of the Optical Society of America B

Model for optical refrigeration of Ho3+-doped fluoride crystals

Guang-Zong Dong, Yuxin Ma, Xin Zhao, Xinlu Zhang

Published Oct 20, 2022• 5 citations
Publisher

Abstract

A novel method for modeling optical refrigeration of H o 3 + -doped fluoride crystals is presented to obtain a laser-induced thermal modulation spectroscopy (LITMoS)-compatible fitting expression of cooling efficiency in a simple way. The quantum-yield frequency that corresponds to the output energy of a specific transition channel is introduced to simplify theoretical derivation. This model takes into account excitation dependency of external quantum efficiency and can be applied in theoretical analysis and experimental data fitting of optical refrigeration systems with multiple 4 f manifolds.

DOI
10.1364/josab.465982

Related papers

Observation of optical refrigeration in a holmium-doped crystal

Saeid Rostami, Alexander R. Albrecht, Azzurra Volpi +1 more

We report the first demonstration of solid-state optical refrigeration of a Ho-doped material. A 1 mol% Ho-doped Yttrium Lithium Fluoride (YLF) crystal is cooled by mid-IR laser radiation, and its external quantum efficiency and parasitic background absorption are evaluated. Using detailed temperature-dependent spectroscopic analysis the minimum achievable temperature of a 1% Ho:YLF sample is estimated. Owing to its narrower ground- and excited-state manifolds, larger absorption cross-section, and coincidence of optimum cooling wavelength of 2070 nm with commercially available high-power and highly efficient Tm-fiber lasers, Ho^3+-doped crystals are superior to Tm^3+-doped systems for mid-IR optical refrigeration. With further improvement in material purity and increased doping concentration, they offer great potential towards enhancing the cooling efficiency nearly two-fold over the best current Yb:YLF systems, achieving lower temperatures as well as for realization of eye-safe mid-IR high-power radiation balanced lasers.

arXiv:1811.05745•Photonics Research•Mar 18, 2019•37 citations

Chapter 8 Bulk Cooling Efficiency Measurements of Yb-Doped Fluoride Single Crystals and Energy Transfer–Assisted Anti-Stokes Cooling in Co-Doped Fluorides

Azzurra Volpi, Alberto Di Lieto, M. Tonelli

To overcome the ETU-induced heating and realize efficient and enhanced laser cooling in Ho3+-doped solids, in Section 4.3, we will provide a modified excitation scheme based on ground-state absorption (GSA) of 5I8 Æ 5I7 at around 2.07 μm and ESA of 5I5 Æ 5F5 at around 2.28 μm. Compared with the conventional pumping scheme, the co-pumping scheme ameliorates the cooling performance significantly through alleviating the upconversion-quenching-induced heat [12], that is, the heat-producing 5I5 Ho3+ions are pumped to the 5F5 state by the laser at 2.28 μm. Fortunately, the 5F5 Ho3+ ions barely transit to the lower nearby state and tend to decay radiatively. Therefore, major heat produced in the conventional laser cooling of Ho3+-doped solids is avoided, and both cooling efficiency and cooling power density can be improved. In Section 4.4, we broaden the research domain of optical refrigeration to rare earth ion co-doped systems. Specifically, when Ho3+–Tm3+ co-doped YLiF4 crystals are pumped at around 2.07 μm, Ho3+ ions will populate at the 5I7 manifold. Meanwhile, Tm3+ ions will also be sensitized by absorbing energy transferred from 5I7 Ho3+ ions. Since the average energy of fluorescence photons generated by Tm3+3F4 Æ 3H6 radiative transitions is higher than that generated by Ho3+5I7 Æ 5I8 radiative transitions, energy transfer (ET) from Ho3+ to Tm3+ ions will induce annihilation of host phonons, and bring enhancement in both the cooling efficiency and the cooling power. Therefore, this cooling mechanism is referred next as energy transfer-enhanced laser cooling (ETLC) of solids [11]. 4.2 Conventional Laser Cooling of Holmium- The main upconversion process and the anti-Stokes fluorescence cooling (ASFC) processes of Ho3+-doped fluoride crystals are illustrated in Fig. 4.1. The ground-state (5I8) Ho3+ ions are pumped to the first excited state (5I7) with laser excitations of energy hν (solid red arrow on the left) and then relax thermally among the Stark levels in a timescale of picoseconds with host phonon absorption. Part of the Ho3+5I7 ions de-excite by emitting fluorescence photons of mean energy hν10 (solid blue arrow, ν10 > ν), which accounts for the ASFC process. The rest of the 5I7 Ho3+ ions de-excited and transfer their energy to the neighboring 5I7 Ho3+ ions, causing population accumulation at the third excited state (5I5) with host phonon absorption (solid green arrows). Comparison between the energy mismatch and the host phonon energy (for YLiF4 crystal host, ħω ≈ 450 cm-1) indicates that about two host phonons are annihilated for each ETU process (see Table 4.1).

Pan Stanford Publishing eBooks•Aug 31, 2016•0 citations

Efficient and enhanced optical refrigeration beyond 2 μm in Ho^3+-doped solids via copumping scheme

Guang-Zong Dong, Xinlu Zhang

We report a theoretical scheme for realizing efficient and enhanced laser cooling in Ho3+-doped solids, based on ground-state absorption (GSA) of I58→I57 at around 2.07 μm and excited-state absorption (ESA) of I55→F55 at around 2.28 μm. The upconversion-quenching-induced heat that usually is found in Ho3+ optical refrigeration can be significantly alleviated by using the copumping scheme, so the cooling power density and the cooling efficiency are greatly improved. The scheme works at temperatures above 133 K, and can shorten the time needed to reach the minimum attainable temperature of the cooling system. Besides, the dopant concentration is allowed to be promoted to around 1%. The copumping scheme can also be applied to other multilevel (such as Tm3+ and Er3+) optical refrigeration systems to improve the cooling performance.

Journal of the Optical Society of America B•Jun 26, 2014•3 citations

Investigation of temperature dependence of quantum efficiency and parasitic absorption in rare-earth doped crystals (Conference Presentation)

Aram Gragossian, Azzurra Volpi, Junwei Meng +4 more

Optical refrigeration of rare-earth doped crystals has exceptional qualities that can be used for building a compact and vibration-free all-solid-state optical cooler. Estimating the lowest achievable temperature and cooling power of such a device requires accurate measurements of external quantum efficiency, mean fluorescence wavelength, and parasitic absorption. Here we discuss temperature dependent measurements of these parameters for a high quality Yb:YLF sample by performing a LITMoS test (Laser Induced Temperature Modulation Spectrum) combined with contact-free differential luminescence thermometry. These measurements are challenging at low temperatures, but by integrating these two methods, we can perform LITMoS test at any temperature.

Optical and Electronic Cooling of Solids•Mar 14, 2018•3 citations

Adaptive four-level modeling of laser cooling of solids

Weiliang Jin, Cheng Guo, Meir Orenstein +1 more

Laser cooling of rare-earth doped solids has been demonstrated across a wide range of material platforms, inspiring the development of simple phenomenological models such as the four-level model to elucidate the universal properties of laser cooling under various operating conditions. However, these models usually require the input of full absorption spectra that must be provided experimentally or by additional complicated atomic modeling. In this Letter, we propose that a four-level model, when extended to admit effective energy levels adaptive to the pumping photon energy, can accurately predict the cooling efficiency as a function of temperature and pumping frequency using only few inputs such as the absorption coefficient measured at a single frequency and temperature. Our model exploits the quasi-equilibrium properties of the excitation of rare-earth ions for the determination of the effective four energy levels. The model is validated against published experimental results for a span of materials including ytterbium/thulium-doped glass and crystals. With the verified model, we derive explicit expressions for the optimal frequency and the operating bandwidth of pumping lasers. Our model significantly simplifies the modeling process of laser cooling and is expected to stimulate further development of optical refrigeration.

arXiv:2109.02702•Applied Physics Letters•Nov 1, 2021•5 citations

Efficient optical refrigeration in Yb3+:YLiF4at cryogenic temperatures via pulsed excitation

Guang-Zong Dong, Kaishun Zou, Juncheng Liu

A theoretical cooling scheme based on pulsed excitation is presented to facilitate efficient optical refrigeration at cryogenic temperatures. The mechanism of optical refrigeration with pulsed excitation is described by a simplified cooling model founded on a density matrix. Simulated results show that for the Yb3+:YLiF4 crystal with doping concentration of 10% and background absorption of 10−4 cm−1, optical refrigeration via picosecond pulsed excitation is competitive at a temperature of lower than 100 K due to its high cooling efficiency and may advance the cooling temperature to the boiling point of nitrogen.

Journal of the Optical Society of America B•Jun 8, 2018•2 citations
A novel method for modeling optical refrigeration of H o 3 + -doped fluoride crystals is presented to obtain a laser-induced thermal modulation spectroscopy (LITMoS)-compatible fitting expression of cooling efficiency in a simple way. The quantum-yield frequency that corresponds to the output energy of a specific transition channel is introduced to simplify theoretical derivation. This model takes into account excitation dependency of external quantum efficiency and can be applied in theoretical analysis and experimental data fitting of optical refrigeration systems with multiple 4 f manifolds.
We report the first demonstration of solid-state optical refrigeration of a Ho-doped material. A 1 mol% Ho-doped Yttrium Lithium Fluoride (YLF) crystal is cooled by mid-IR laser radiation, and its external quantum efficiency and parasitic background absorption are evaluated. Using detailed temperature-dependent spectroscopic analysis the minimum achievable temperature of a 1% Ho:YLF sample is estimated. Owing to its narrower ground- and excited-state manifolds, larger absorption cross-section, and coincidence of optimum cooling wavelength of 2070 nm with commercially available high-power and highly efficient Tm-fiber lasers, Ho^3+-doped crystals are superior to Tm^3+-doped systems for mid-IR optical refrigeration. With further improvement in material purity and increased doping concentration, they offer great potential towards enhancing the cooling efficiency nearly two-fold over the best current Yb:YLF systems, achieving lower temperatures as well as for realization of eye-safe mid-IR high-power radiation balanced lasers.
To overcome the ETU-induced heating and realize efficient and enhanced laser cooling in Ho3+-doped solids, in Section 4.3, we will provide a modified excitation scheme based on ground-state absorption (GSA) of 5I8 Æ 5I7 at around 2.07 μm and ESA of 5I5 Æ 5F5 at around 2.28 μm. Compared with the conventional pumping scheme, the co-pumping scheme ameliorates the cooling performance significantly through alleviating the upconversion-quenching-induced heat [12], that is, the heat-producing 5I5 Ho3+ions are pumped to the 5F5 state by the laser at 2.28 μm. Fortunately, the 5F5 Ho3+ ions barely transit to the lower nearby state and tend to decay radiatively. Therefore, major heat produced in the conventional laser cooling of Ho3+-doped solids is avoided, and both cooling efficiency and cooling power density can be improved. In Section 4.4, we broaden the research domain of optical refrigeration to rare earth ion co-doped systems. Specifically, when Ho3+–Tm3+ co-doped YLiF4 crystals are pumped at around 2.07 μm, Ho3+ ions will populate at the 5I7 manifold. Meanwhile, Tm3+ ions will also be sensitized by absorbing energy transferred from 5I7 Ho3+ ions. Since the average energy of fluorescence photons generated by Tm3+3F4 Æ 3H6 radiative transitions is higher than that generated by Ho3+5I7 Æ 5I8 radiative transitions, energy transfer (ET) from Ho3+ to Tm3+ ions will induce annihilation of host phonons, and bring enhancement in both the cooling efficiency and the cooling power. Therefore, this cooling mechanism is referred next as energy transfer-enhanced laser cooling (ETLC) of solids [11]. 4.2 Conventional Laser Cooling of Holmium- The main upconversion process and the anti-Stokes fluorescence cooling (ASFC) processes of Ho3+-doped fluoride crystals are illustrated in Fig. 4.1. The ground-state (5I8) Ho3+ ions are pumped to the first excited state (5I7) with laser excitations of energy hν (solid red arrow on the left) and then relax thermally among the Stark levels in a timescale of picoseconds with host phonon absorption. Part of the Ho3+5I7 ions de-excite by emitting fluorescence photons of mean energy hν10 (solid blue arrow, ν10 > ν), which accounts for the ASFC process. The rest of the 5I7 Ho3+ ions de-excited and transfer their energy to the neighboring 5I7 Ho3+ ions, causing population accumulation at the third excited state (5I5) with host phonon absorption (solid green arrows). Comparison between the energy mismatch and the host phonon energy (for YLiF4 crystal host, ħω ≈ 450 cm-1) indicates that about two host phonons are annihilated for each ETU process (see Table 4.1).
We report a theoretical scheme for realizing efficient and enhanced laser cooling in Ho3+-doped solids, based on ground-state absorption (GSA) of I58→I57 at around 2.07 μm and excited-state absorption (ESA) of I55→F55 at around 2.28 μm. The upconversion-quenching-induced heat that usually is found in Ho3+ optical refrigeration can be significantly alleviated by using the copumping scheme, so the cooling power density and the cooling efficiency are greatly improved. The scheme works at temperatures above 133 K, and can shorten the time needed to reach the minimum attainable temperature of the cooling system. Besides, the dopant concentration is allowed to be promoted to around 1%. The copumping scheme can also be applied to other multilevel (such as Tm3+ and Er3+) optical refrigeration systems to improve the cooling performance.
Optical refrigeration of rare-earth doped crystals has exceptional qualities that can be used for building a compact and vibration-free all-solid-state optical cooler. Estimating the lowest achievable temperature and cooling power of such a device requires accurate measurements of external quantum efficiency, mean fluorescence wavelength, and parasitic absorption. Here we discuss temperature dependent measurements of these parameters for a high quality Yb:YLF sample by performing a LITMoS test (Laser Induced Temperature Modulation Spectrum) combined with contact-free differential luminescence thermometry. These measurements are challenging at low temperatures, but by integrating these two methods, we can perform LITMoS test at any temperature.
Laser cooling of rare-earth doped solids has been demonstrated across a wide range of material platforms, inspiring the development of simple phenomenological models such as the four-level model to elucidate the universal properties of laser cooling under various operating conditions. However, these models usually require the input of full absorption spectra that must be provided experimentally or by additional complicated atomic modeling. In this Letter, we propose that a four-level model, when extended to admit effective energy levels adaptive to the pumping photon energy, can accurately predict the cooling efficiency as a function of temperature and pumping frequency using only few inputs such as the absorption coefficient measured at a single frequency and temperature. Our model exploits the quasi-equilibrium properties of the excitation of rare-earth ions for the determination of the effective four energy levels. The model is validated against published experimental results for a span of materials including ytterbium/thulium-doped glass and crystals. With the verified model, we derive explicit expressions for the optimal frequency and the operating bandwidth of pumping lasers. Our model significantly simplifies the modeling process of laser cooling and is expected to stimulate further development of optical refrigeration.
A theoretical cooling scheme based on pulsed excitation is presented to facilitate efficient optical refrigeration at cryogenic temperatures. The mechanism of optical refrigeration with pulsed excitation is described by a simplified cooling model founded on a density matrix. Simulated results show that for the Yb3+:YLiF4 crystal with doping concentration of 10% and background absorption of 10−4 cm−1, optical refrigeration via picosecond pulsed excitation is competitive at a temperature of lower than 100 K due to its high cooling efficiency and may advance the cooling temperature to the boiling point of nitrogen.