Oguzhan Kara

Dual-comb mid-infrared spectroscopy with free-running oscillators and absolute optical calibration from a radio-frequency reference

By using free-running femtosecond OPOs with a repetition-rate difference of ∼500 Hz we demonstrate methane absorption spectroscopy at a resolution < 0.08 cm−1, fully calibrated in the optical domain from repetition-rate and carrier-envelope-offset frequency measurements.

Singly and doubly resonant femtosecond optical parametric oscillators for precision spectroscopy from the near-to mid-infrared

Optical parametric oscillators (OPOs), pumped by Ti:sapphire and Yb-doped femtosecond lasers, provide unique capabilities to address a broad range of parameters of interest to precision spectroscopy. We review here a variety of OPOs under development that offer tuning from 1.5 to 13 μm, repetition rates from 100 MHz to 10 GHz and pulse durations from < 25 fs to a few picoseconds. Spectroscopic techniques revealing the individual frequency comb modes are discussed, along with dual-comb spectroscopy at 3 μm and from 6-8 μm.

Chemical detection using broadband femtosecond optical parametric oscillators in the 6-12-micron spectral fingerprint region

The broad and slowly varying spectral features of liquids and solids require broadband sources in the mid- to long-wave infrared for their detection and identification. We present here a range of measurements made using uniquely tunable femtosecond optical parametric oscillators, which have enabled stand-off Fourier-transform spectroscopy to be implemented across a large part of the spectral fingerprint region. In this way we have achieved active stand-off detection of liquids on surfaces, of powders and of airborne liquid particles in aerosol form. We discuss the optical parametric oscillator technology, the spectroscopy implementations and the detection capabilities and limitations of the techniques.

Mid-infrared dual-comb spectroscopy with microwave-referenced wavelength calibration

Dual-comb spectroscopy (DCS) [1] uses asynchronous broadband coherent sources to achieve Fourier-transform-like spectroscopy but with no moving parts and near-kHz acquisition rates [2]. Here we demonstrate dual-comb mid-infrared spectroscopy of methane gas using two free-running optical parametric oscillators (OPOs) with a repetition-rate difference of 500 Hz and complete optical calibration from a microwave reference.

Optical Frequency Combs Based on Femtosecond Optical Parametric Oscillators

The development of femtosecond frequency combs based on optical parametric oscillators (OPOs) in our group is summarized. Dual combs generated in a single OPO cavity have been showed applications in precise spectroscopy.