Quantum-noise-limited cavity ring-down spectroscopy | NIST

Roger D. van Zee, J. P. Looney

David A. Long, Adam J. Fleisher, Szymon Wójtewicz +2 more

We present an ultrasensitive cavity-enhanced technique for probing weak molecular absorptions. Recently, we have implemented heterodyne detection, which allowed for quantum-noise-limited detection and noise-equivalent absorption coefficients as low as 6×10−14 cm−1•Hz−1/2.

J. J. Bollinger

Johannes Burkart, D. Romanini, S. Kassi

We introduce optical feedback frequency stabilized cavity ring-down spectroscopy (OFFS-CRDS), a near-shot-noise-limited technique that combines kilohertz resolution with an absorption detection sensitivity of 5×10(-13) cm(-1) Hz(-1/2). Its distributed feedback laser source is stabilized to a highly stable V-shaped reference cavity by optical feedback and fine-tuned by means of single-sideband modulation. The stability of this narrow laser is transferred to a ring-down (RD) cavity using a new fibered Pound-Drever-Hall (PDH) locking scheme without a dedicated electro-optic phase modulator, yielding several hundred RD events per second. We demonstrate continuous coverage of more than 7 nm with a baseline noise of 5×10(-12) cm(-1) and a dynamic range spanning six decades. With its resonant intracavity light intensity on the order of 1 kW/cm2, the spectrometer was used for observing a Lamb dip in a transition of carbon dioxide involving four vibrational quanta. Saturating such a weak transition at 160 μW input power, OFFS-CRDS paves the way to Doppler-free molecular overtone spectroscopy for precision measurements of hyperfine structures and pressure shifts.

Kevin K. Lehmann

R. Harris, J. Niemeyer