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arXiv:2505.24083 · Physical Review A

Purcell enhancement and suppression in laser cooling of Yb 3 + :YLF nanocrystals in a Fabry-Pérot microcavity

Lucas R. Mendicino, Franco Mayo, Christian Tomás Schmiegelow, Augusto J. Roncaglia

Published Nov 3, 2025• 0 citations
arXivHTMLPDF

Abstract

We investigate the improvement of anti-Stokes laser cooling of a ${\mathrm{Yb}}^{3+}$:YLF nanocrystal in a Fabry-P\'erot microcavity via the Purcell effect. Our analysis accounts for both the enhancement of emission lines resonant with the cavity transmission and the suppression of off-resonance emissions. Using a quantum-mechanical framework, we modeled the ${\mathrm{Yb}}^{3+}$ ions in a ${\mathrm{YLiF}}_{4}$ matrix and the laser system to calculate the minimum achievable temperature and cooling efficiency, incorporating cavity-induced modifications to experimental data on the emission cross section. Our results indicate that for temperatures below 100 K, the cooling efficiency $\ensuremath{\eta}$ is consistently enhanced, and the minimum achievable temperature is reduced comfortably below the current limits. We also show how the inclusion of Purcell inhibition effects can lead to improvements in the cooling efficiency ranging from 25% to 65% with respect to the case when only Purcell enhancement is considered.

DOI
10.1103/gsfd-fmmk

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We investigate the improvement of anti-Stokes laser cooling of a Yb3+{\mathrm{Yb}}^{3+}Yb3+:YLF nanocrystal in a Fabry-P'erot microcavity via the Purcell effect. Our analysis accounts for both the enhancement of emission lines resonant with the cavity transmission and the suppression of off-resonance emissions. Using a quantum-mechanical framework, we modeled the Yb3+{\mathrm{Yb}}^{3+}Yb3+ ions in a YLiF4{\mathrm{YLiF}}_{4}YLiF4​ matrix and the laser system to calculate the minimum achievable temperature and cooling efficiency, incorporating cavity-induced modifications to experimental data on the emission cross section. Our results indicate that for temperatures below 100 K, the cooling efficiency \ensuremathη\ensuremath{\eta}\ensuremathη is consistently enhanced, and the minimum achievable temperature is reduced comfortably below the current limits. We also show how the inclusion of Purcell inhibition effects can lead to improvements in the cooling efficiency ranging from 25% to 65% with respect to the case when only Purcell enhancement is considered.
Optical refrigeration of solids with anti-Stokes fluorescence has been widely explored as a vibration-free cryogenic cooling technology. A minimum temperature of 87 K has been demonstrated with rare-earth-ion-doped crystals using optical refrigeration. However, the depletion of the upper-lying energy levels in the ground-state manifold hinders further cooling to below the liquid nitrogen ( LN 2 ) temperatures, restricting its applications. In this work, we introduce a Purcell-enhanced optical refrigeration method to circumvent this limitation. This approach enhances the emission of high-energy photons by coupling the emitters to an optical cavity, blueshifting the mean emission wavelength. Such Purcell-enhanced emission facilitates cooling starting from a lower-energy level in the ground-state manifold, which exhibits a higher occupation below the LN 2 temperatures. Using experimentally measured optical coefficients, our theoretical analysis predicts a minimum achievable internal temperature of about 38 K for a Yb 3 + : YLiF 4 nanocrystal near a cavity under realistic conditions. The proposed method is applicable to other rare-earth-ion-doped materials and semiconductors and will have applications in creating superconducting and other quantum devices through solid-state cooling.
We study the behavior of a single laser-driven trapped ion inside a microscopic optical Fabry-Perot cavity. In particular, we demonstrate a fiber Fabry-Perot cavity operating on the principal ${S}_{1/2}\ensuremath{\rightarrow}{P}_{1/2}$ electric dipole transition of an Yb+{\mathrm{Yb}}^{+}Yb+ ion at 369 nm with an ion-cavity coupling strength of $g=2\ensuremath{\pi}\ifmmode\times\else\texttimes\fi{}67(1)$ MHz. We employ the cavity to study the generation of single photons and observe cavity-induced backaction in the Purcell-enhanced emission of photons. Tuning of the amplitude and phase between the driving field and the cavity field built up from photons scattered into the cavity mode by the ion allows us to enhance or suppress the total rate of photon emission from the ion-cavity system.
This thesis investigates the coupling of the fluorescence of nitrogen-vacancy (NV) centers in diamond to tunable optical microresonators at ambient conditions, in particular in the regime of Purcell enhancement. We use fiber-based, open-access Fabry-Pérot cavities optimized for high finesse and ultra-small mode volume. Different regimes of cavity enhancement are studied that are complementary to each other: A first experiment relies on a high-finesse cavity with dielectric mirrors. The scaling laws of Purcell enhancement are explicitly demonstrated by a large-range variation of both the cavity mode volume (V = 16 − 600 µm^3 ) and the quality factor (Q = 6 · 10^3 − 2 · 10^6). We detect an enhancement of the emission spectral density by up to a factor of 300. The full potential of this resonator can be exploited with emitters having a linewidth which is narrower than the resonance linewidth of the cavity. This concept holds promise for the implementation of wavelength-tunable, narrow-band single-photon sources as well as the generation of indistinguishable single-photons at ambient conditions. However, for broad-band emitters like the NV center at room temperature, the emission lifetime is not affected noticeably in this configuration. In order to directly observe lifetime changes and Purcell-enhanced single-photon emission, we manufacture fiber-based cavities with silver-coated mirrors having ultra-small mode volumes, as small as V = 1.0 λ^3 = 0.34 µm^3. We demonstrate cavity-enhanced fluorescence imaging, which allows to locate and analyze several single NV centers with one cavity. The Purcell effect is evidenced by an enhanced fluorescence collection of up to 1.6 · 10^6 photons per second from single-NV centers and a tunable variation of the emission lifetime corresponding to an effective Purcell factor of up to 2. We furthermore investigate a benefcial regime of optical confinement where the Fabry-Pérot cavity mode is combined with additional mode confinement by the diamond nanocrystal itself, enabling sub-λ^3 mode volumes. We perform simulations that predict effective Purcell factors of up to 11 for NV centers and of up to 63 for silicon-vacancy centers, revealing a great potential for bright single-photon sources and effcient spin readout at ambient conditions.
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.
We report on the coupling of the emission from a single europium-doped nanocrystal to a fiber-based microcavity under cryogenic conditions. As a first step, we study the properties of nanocrystals that are relevant for cavity experiments and show that embedding them in a dielectric thin film can significantly reduce scattering loss and increase the light–matter coupling strength for dopant ions. The latter is supported by the observation of a fluorescence lifetime reduction, which is explained by an increased local field strength. We then couple an isolated nanocrystal to an optical microcavity, determine its size and ion number, and perform cavity-enhanced spectroscopy by resonantly coupling a cavity mode to a selected transition. We measure the inhomogeneous linewidth of the coherent transition and find a value that agrees with the linewidth in bulk crystals, evidencing a high crystal quality. We detect the fluorescence from an ensemble of few ions in the regime of power broadening and observe an increased fluorescence rate consistent with Purcell enhancement. The results represent an important step towards the efficient readout of single rare earth ions with excellent optical and spin coherence properties, which is promising for applications in quantum communication and distributed quantum computation.
We report on the coupling of the emission from a single europium-doped nanocrystal to a fiber-based microcavity under cryogenic conditions.As a first step, we study the properties of nanocrystals that are relevant for cavity experiments and show that embedding them in a dielectric thin film can significantly reduce scattering loss and increase the light-matter coupling strength for dopant ions.The latter is supported by the observation of a fluorescence lifetime reduction, which is explained by an increased local field strength.We then couple an isolated nanocrystal to an optical microcavity, determine its size and ion number, and perform cavity-enhanced spectroscopy by resonantly coupling a cavity mode to a selected transition.We measure the inhomogeneous linewidth of the coherent D F 5 0 7 0 -transition and find a value that agrees with the linewidth in bulk crystals, evidencing a high crystal quality.We detect the fluorescence from an ensemble of few ions in the regime of power broadening and observe an increased fluorescence rate consistent with Purcell enhancement.The results represent an important step towards the efficient readout of single rare earth ions with excellent optical and spin coherence properties, which is promising for applications in quantum communication and distributed quantum computation.