Abstract
We present a simple, high-duty-cycle, cavity-enhanced optical absorption measurement technique based on delay-limited Pound-Drever-Hall (PDH) sideband locking. The chosen circuit naturally provides realtime readout of the amplitude quadrature of the PDH error signal, which can be mapped onto the cavity’s internal loss rate while using the phase quadrature to lock sideband frequency to the cavity mode. Our proofof-concept device comprises a 5-cm-long Fabry-Perot cavity with a 450 kHz bandwidth (finesse 6800, 350 ns power ringdown), and a feedback bandwidth of several MHz, limited primarily by the group delay of our electronics. This technique could readily be applied to other optical resonators such as fiber cavities, with potential applications in radiation dosimetry.
Highlights
We work on the development of a time resolved cavityenhanced absorption sensing technique based on PoundDrever-Hall (PDH) sideband locking.PDH locking [1] relies on phase modulation of a laser beam and posterior demodulation of the power reflected from an optical cavity by mixing with a local oscillator at the same modulation frequency
With the correct choice of phase for the local oscillator, the resulting mixed-down voltage provides a derivative-like signal that can be used to lock the cavity on resonance to an incoming laser beam
The amplitude quadrature has a Lorentzian shape about the detuning of the sideband, and provides a non-zero signal when the sideband is locked to the cavity
Summary
We work on the development of a time resolved cavityenhanced absorption sensing technique based on PoundDrever-Hall (PDH) sideband locking. PDH locking [1] relies on phase modulation of a laser beam and posterior demodulation of the power reflected from an optical cavity by mixing with a local oscillator at the same modulation frequency. The amplitude quadrature has a Lorentzian shape about the detuning of the sideband (at modulation frequency Ω), and provides a non-zero signal when the sideband is locked to the cavity. This signal carries real-time information from the cavity and can be mapped onto the cavity’s internal losses
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