Coherent heterodyne-assisted pulsed spectroscopy: sub-Doppler two-photon spectra of krypton, characterizing a tunable nonlinear-optical ultraviolet light source

A chirp-minimized, nanosecond-pulsed system has been developed to generate tunable coherent ultraviolet light at ∼212.5 nm by fourth-harmonic conversion of output from an amplified, injection-seeded optical parametric oscillator (OPO). Our CHAPS (coherent heterodyneassisted pulsed spectroscopy) method is used to characterize the frequency stability and optical bandwidth of the system’s output radiation by recording sub-Doppler twophoton excitation spectra of krypton. In our new scannedreference variant of CHAPS, the central frequency for each amplified OPO pulse is logged by the optical-heterodyne chirp-analysis software, with the frequency of the seed laser slowly tuned and monitored by a high-resolution wavemeter, unlike our previous implementation of CHAPS where the seed-laser frequency was fixed. For the amplified, upconverted pulses at ∼212.5 nm, our CHAPS measurements indicate an optical bandwidth of ∼100 MHz, consistent with the Fourier-transform limit of their duration (∼4.5 ns). Y. He · B.J. Orr ( ) MQ Photonics Research Centre, Department of Physics and Engineering, Macquarie University, Sydney, NSW 2109, Australia e-mail: [email protected] Fax: +61-2-9850-8289 M. Kono · M.J. Sellars · K.G.H. Baldwin Research School of Physics and Engineering, The Australian National University, Canberra, ACT 0200, Australia R.T. White Institute for Photonics and Advanced Sensing (IPAS), University of Adelaide, Adelaide, SA 5005, Australia