Abstract
We present a new technique suitable for generating broadband phase- and frequency-locked frequency combs in the mid-infrared. Our source is based on a degenerate optical parametric oscillator (OPO) which rigorously both down-converts and augments the spectrum of a pump frequency comb provided by a commercial mode-locked near-IR laser. Low intracavity dispersion, combined with extensive cross-mixing of comb components, results in extremely broad instantaneous mid-IR bandwidths. We achieve an output power of 60 mW and 20 dB bandwidth extending from 2500 to 3800 nm. Among other applications, such a source is well-suited for coherent Fourier-transform spectroscopy in the absorption-rich mid-IR 'molecular fingerprint' region.
Highlights
The broadband and coherent nature of frequency combs produced in the visible and nearinfrared – both in frequency and in time – has allowed a revolution in precision metrology
We present a new technique suitable for generating broadband phase- and frequency-locked frequency combs in the mid-infrared
Our source is based on a degenerate optical parametric oscillator (OPO) which rigorously both down-converts and augments the spectrum of a pump frequency comb provided by a commercial mode-locked near-IR laser
Summary
The broadband and coherent nature of frequency combs produced in the visible and nearinfrared – both in frequency (a manifold of spaced narrow frequency-comb lines) and in time (a strictly periodic train of pulses with stable carrier-envelope phase) – has allowed a revolution in precision metrology. Extending the operating range of optical frequency combs to wavelengths > 2 μm is advantageous for a wide range of applications including coherent molecular spectroscopy and trace gas detection in the 'fingerprint' region [1,2], attosecond physics [3], and laser-driven particle acceleration [4]. It has since been shown that a degenerate OPO is a nearly ideal phase-locked frequency divider for single-frequency CW radiation [15]. Extending on our earlier demonstration of a self-phase-locked broadband nearIR subharmonic OPO pumped by a Ti:Sapphire laser [16,17] this work shows that with proper design, a synchronously-pumped frequency-divide-by-two OPO proves useful for transposing near-IR frequency combs to the mid-infrared
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