Abstract
High-resolution spectroscopy in the 1–10 μm region has never been fully tackled for the lack of widely-tunable and practical light sources. Indeed, all solutions proposed thus far suffer from at least one of three issues: they are feasible only in a narrow spectral range; the power available for spectroscopy is limited; the frequency accuracy is poor. Here, we present a setup for high-resolution spectroscopy, whose approach can be applied in the whole 1–10 μm range. It combines the power of quantum cascade lasers (QCLs) and the accuracy achievable by difference frequency generation using an orientation patterned GaP crystal. The frequency is measured against a primary frequency standard using the Italian metrological fibre link network. We demonstrate the performance of the setup by measuring a vibrational transition in a highly-excited metastable state of CO around 6 μm with 11 digits of precision.
Highlights
The fractional accuracy on spectroscopic measurements on atoms has reached the few parts in 1018 1; the same quantity in experiments on molecules is worse by more than three orders of magnitude[2,3,4,5,6,7]
In order to achieve a level of precision typical of atomic physics experiments, one needs a cold molecular sample combined with state-of-the-art light sources in the mid IR8
While RF oscillators disciplined by the Global Positioning System (GPS) can achieve 10−14 stability and accuracy only after tens of thousands seconds integration times, the same stability and accuracy are reached in 1 second by using an optical dissemination of the frequency standard, and the intrinsic uncertainty of the disseminated clock is reached with short interaction times[3,21,23]
Summary
We lock two near-IR lasers to a frequency comb whose repetition rate is referenced and stabilized using the fibre link The light of these two lasers is mixed in an OP-GaP crystal to generate the difference of their frequency, which lies in the mid IR. At LENS, we phase-lock a diode laser to the incoming radiation, replicating the stability of the link laser and boosting the optical power at a suitable level for referencing a frequency comb. In an OP-GaP crystal we generate the difference frequency of two mid IR lasers, a Nd:YAG MOPA system at 1064 nm with a linewidth of 1 kHz and operated at a power of about 5 W (pump), and a diode laser at 1220– 1320 nm delivering about 30 mW (signal). We remark that QCL linewidth and jitter at the kHz level can be further improved by referencing the frequency comb to an ultra narrow optical-link-disciplined laser around the Nd:YAG frequency
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
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 callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
