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1. Resonance theory and quantum dynamics simulations of vibrational polariton chemistry

   https://doi.org/10.1063/5.0159791  

   Ying, Wenxiang; Huo, Pengfei (August 2023, The Journal of Chemical Physics)

   We present numerically exact quantum dynamics simulations using the hierarchical equation of motion approach to investigate the resonance enhancement of chemical reactions due to the vibrational strong coupling (VSC) in polariton chemistry. The results reveal that the cavity mode acts like a “rate-promoting vibrational mode” that enhances the ground state chemical reaction rate constant when the cavity mode frequency matches the vibrational transition frequency. The exact simulation predicts that the VSC-modified rate constant will change quadratically as the light–matter coupling strength increases. When changing the cavity lifetime from the lossy limit to the lossless limit, the numerically exact results predict that there will be a turnover of the rate constant. Based on the numerical observations, we present an analytic rate theory to explain the observed sharp resonance peak of the rate profile when tuning the cavity frequency to match the quantum transition frequency of the vibrational ground state to excited states. This rate theory further explains the origin of the broadening of the rate profile. The analytic rate theory agrees with the numerical results under the golden rule limit and the short cavity lifetime limit. To the best of our knowledge, this is the first analytic theory that is able to explain the sharp resonance behavior of the VSC-modified rate profile when coupling an adiabatic ground state chemical reaction to the cavity. We envision that both the numerical analysis and the analytic theory will offer invaluable theoretical insights into the fundamental mechanism of the VSC-induced rate constant modifications in polariton chemistry. 

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2. High peak power, sub-ps green emission in a passively mode locked W-cavity VECSEL

   https://doi.org/10.1364/OE.384439  

   Meyer, Jason_T; Lukowski, Michal_L; Hessenius, Chris; Wright, Ewan_M; Fallahi, Mahmoud (February 2020, Optics Express)

   We report on the experimental results of a passively mode-locked vertical external cavity surface emitting laser (VECSEL), implemented in a W-cavity configuration, using a lithium triborate (LBO) crystal for intra-cavity second harmonic generation (SHG) at 528 nm. The W-cavity configuration allows separation of the crystal from the semiconductor saturable absorber mirror (SESAM), enabling independent control over the Gaussian beam sizes at the crystal, chip, and SESAM. This optimized cavity demonstrated a second harmonic pulse width of ~760 fs at a frequency of 465 MHz and 230 mW average output power, resulting in a peak pulse power of 580 W. 

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3. Widely tunable cavity-enhanced frequency combs

   https://doi.org/10.1364/OL.389412  

   Silfies, Myles_C; Kowzan, Grzegorz; Chen, Yuning; Lewis, Neomi; Hou, Ryan; Baehre, Robin; Gross, Tobias; Allison, Thomas_K (April 2020, Optics Letters)

   We describe the cavity enhancement of frequency combs over a wide tuning range of 450–700 nm ( $><\#comment/>7900{\mathrm{c}\mathrm{m}}^{-<\#comment/>1}$), covering nearly the entire visible spectrum. Tunable visible frequency combs from a synchronously pumped optical parametric oscillator are coupled into a four-mirror, dispersion-managed cavity with a finesse of 600–1400. An intracavity absorption path length enhancement greater than 190 is obtained over the entire tuning range, while preserving intracavity spectral bandwidths capable of supporting sub-200 fs pulse durations. These tunable cavity-enhanced frequency combs can find many applications in nonlinear optics and spectroscopy. 

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4. Interferometric differential high-frequency lock-in probe for laser-induced vacuum birefringence

   https://doi.org/10.1103/PhysRevResearch.7.023026  

   Bullis, R G; Jentschura, U D; Yost, D C (April 2025, Physical Review Research)

   We propose a measurement of laser-induced vacuum birefringence through the use of pulsed lasers coupled to femtosecond optical enhancement cavities. This measurement technique features cavity-enhanced pump and probe pulses, as well as an independent control pulse. The control pulse allows for a differential measurement where the final signal is obtained using high-frequency lock-in detection, greatly mitigating time-dependent cavity birefringence as an important and possibly prohibitive systematic effect. In addition, the method features the economical use of laser power and results in a relatively simple experimental setup. 

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5. Ultrafast structured light through nonlinear frequency generation in an optical enhancement cavity

   https://doi.org/10.1364/OL.531092  

   Jones, Walker_M; Reber, Melanie_A_R (August 2024, Optics Letters)

   The generation of shaped laser beams, or structured light, is of interest in a wide range of fields, from microscopy to fundamental physics. There are several ways to make shaped beams, most commonly using spatial light modulators comprised of pixels of liquid crystals. These methods have limitations on the wavelength, pulse duration, and average power that can be used. Here we present a method to generate shaped light that can be used at any wavelength from the UV to IR, on ultrafast pulses, and a large range of optical powers. By exploiting the frequency difference between higher-order modes, a result of the Gouy phase, and cavity mode matching, we can selectively couple into a variety of pure and composite higher-order modes. Optical cavities are used as a spatial filter and then combined with sum-frequency generation in a nonlinear crystal as the output coupler to the cavity to create ultrafast, frequency comb structured light. 

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