Abstract
We propose and characterize experimentally a new source of optical frequency combs for performing multi-heterodyne spectrometry. This comb modality is based on a frequency-shifting loop seeded with a continuous-wave (CW) monochromatic laser. The comb lines are generated by successive passes of the CW laser through an acousto-optic frequency shifter. We report the generation of frequency combs with more than 1500 mutually coherent lines, without resorting to non-linear broadening phenomena or external electronic modulation. The comb line spacing is easily reconfigurable from tens of MHz down to the kHz region. We first use a single acousto-optic frequency comb to conduct self-heterodyne interferometry with a high frequency resolution (500 kHz). By increasing the line spacing to 80 MHz, we demonstrate molecular spectroscopy on the sub-millisecond time scale. In order to reduce the detection bandwidth, we subsequently implement an acousto-optic dual-comb spectrometer with the aid of two mutually coherent frequency shifting loops. In each architecture, the potentiality of acousto-optic frequency combs for spectroscopy is validated by spectral measurements of hydrogen cyanide in the near-infrared region.
Highlights
Optical frequency combs (FCs) have become key measurement tools in optical metrology and high-precision spectroscopy
A different way of generating phase-locked FCs with controlled absolute frequency consists of seeding a high-finesse resonator with a CW laser: regularly spaced comb lines are generated by non-linear interactions in the resonator
The generation of acousto-optics FCs is based on a fiber frequency-shifting loop (FSL) [Fig. 1(a)]
Summary
Optical frequency combs (FCs) have become key measurement tools in optical metrology and high-precision spectroscopy. The extension to molecular spectroscopy has been subsequently demonstrated with a hybrid dual-comb setup, including a mode-locked frequency comb [31] In these phase modulation techniques the spectral bandwidth of the FC is limited by the bandwidth of the function generator (a few tens of GHz). Another approach that has been proposed to produce FCs from a CW laser combines gain-switching and optical injection locking in a semiconductor laser [32, 33]. We propose and implement a simple source of optical FCs, providing more than 1000 mutually coherent lines from a single CW laser, with a FSR reconfigurable in the range from kHz to tens of MHz. Our technique makes no use of non-linear media, nor fast electronic function generators. The prospects of acousto-optic frequency combs for spectroscopic and metrology applications, along with their limitations, are briefly discussed
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
