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Register a new userSub-kHz linewidth narrowing of a mid-infrared OPO idler frequency by direct cavity stabilization
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We stabilize the idler frequency of a singly-resonant optical parametric oscillator directly to the resonance of a mid-infrared Fabry-Perot reference cavity. This is accomplished by the Pound-Drever-Hall locking scheme, controlling either the pump laser or the resonant signal frequency. A residual relative frequency noise power spectral density below 10$^3$ Hz$^2$/Hz is reached, with a Gaussian linewidth of 920 Hz over 100 ms, which demonstrates the potential for reaching spectral purity down to the Hz level by locking the optical parametric oscillator against a mid-infrared cavity with state-of-the-art superior performance.
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A guided-wave chip laser operating in a single longitudinal mode at 2860 nm is presented. The cavity was set in the Littman-Metcalf configuration to achieve single-frequency operation with a side-mode suppression ratio above 33 dB. The chip lasers linewidth was found to be limited by mechanical fluctuations, but its Lorentzian contribution was estimated to be lower than 1 Hz using a heterodyne technique. This demonstration incorporates a high coherence source with the simplicity provided by the compactness of chip lasers.
An experimental method is developed for the robust frequency stabilization using a high-finesse cavity when the laser exhibits large intermittent frequency jumps. This is accomplished by applying an additional slow feedback signal from Doppler-free fluorescence spectroscopy in an atomic beam with increased frequency locking range. As a result, a stable and narrow-linewidth 556 nm laser maintains the frequency lock status for more than a week, and contributes to more accurate evaluation of the Yb optical lattice clock. In addition, the reference optical cavity is supported at vibration-insensitive points without any vibration isolation table, making the laser setup more simple and compact.
We perform a quantum-theoretical treatment of cavity linewidth narrowing with intracavity electromagnetically induced transparency (EIT). By means of intracavity EIT, the photons in the cavity are in the form of cavity polaritons: bright-state polariton and dark-state polariton. Strong coupling of the bright-state polariton to the excited state induces an effect known as vacuum Rabi splitting, whereas the dark-state polariton decoupled from the excited state induce a narrow cavity transmission window. Our analysis would provide a quantum theory of linewidth narrowing with a quantum field pulse at the single-photon level.
We report ultra-stable locking of a commercially available extended cavity diode laser to a vibration-insensitive high finesse Fabry-Perot cavity. A servo bandwidth of 2 MHz is demonstrated. The absolute stability of the diode laser after locking is measured with a three-cornered-hat method. The resulting Allan deviation reaches a level of $2.95times10^{-15}$ at 1 s, corresponding to only 0.93 Hz linewidth, even without vibration isolation of the reference cavity.
Mid-infrared laser frequency combs are compelling sources for precise and sensitive metrology with applications in molecular spectroscopy and spectro-imaging. The infrared atmospheric window between 3-5.5 $mu$m in particular provides vital information regarding molecular composition. Using a robust, fiber-optic source of few-cycle pulses in the near-infrared, we experimentally demonstrate ultra-broad bandwidth nonlinear phenomena including harmonic and difference frequency generation in a single pass through periodically poled lithium niobate (PPLN). These $chi^{(2)}$ nonlinear optical processes result in the generation of frequency combs across the mid-infrared atmospheric window which we employ for dual-comb spectroscopy of acetone and carbonyl sulfide with resolution as high as 0.003 cm$^{-1}$. Moreover, cascaded $chi^{(2)}$ nonlinearities in the same PPLN directly provide the carrier-envelope offset frequency of the near-infrared driving pulse train in a compact geometry.
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