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

Abstract

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).

Sub-Doppler two-photon spectroscopy of 33 Rydberg levels in atomic xenon excited at 205–213 nm: diverse isotopic and hyperfine structure

“…Wavelength-conversion methods to generate narrowband coherent tunable nanosecond-pulsed UV radiation (and, after χ (3) -type nonlinear-optical upconversion in noble-gas atoms [23,24], radiation in the vacuum-and extreme-UV regions) have traditionally depended on pulsed dye laser oscillators/amplifiers [6,8,10,[22][23][24][25], but higherperformance all-solid-state systems have evolved over the last few years [7,9,21,19,23,26].…”

“…In the present work, we have used an all-solid-state coherent UV source, similar to that in our previous study of Kr [21]. In brief, tunable SLM coherent light pulses are generated using a chirp-controllable pulsed optical parametric oscillator (OPO) based on a periodically poled KTiOPO 4 (PP KTP) crystal in a compact ring cavity [19,20].…”

“…A custom-built two-stage multipass Ti:sapphire amplifier system (Amplitude Technologies) boosts the OPO-output pulse energy from <10 μJ to ∼45 mJ. However, the pulse duration deteriorates from >20 ns fwhm for the direct output from the OPO to ∼6 ns fwhm after amplification [21]. This fundamental light (at λ IR = 820-852 nm) is frequency-doubled twice to yield ∼1 mJ of tunable pulsed coherent UV light (at λ UV = 205-213 nm), via two successive nonlinear-optical crystals, LiB 3 O 5 (LBO) and β-BaB 2 O 4 (BBO).…”

“…Our experiments use a previously developed all-solidstate nonlinear-optical light source that produces tunable narrowband single-longitudinal-mode (SLM) pulses (with ∼25-ns duration and 5-μJ energy) at λ IR in the fundamental infrared (IR) wavelength range of 820-850 nm. Its output can be amplified and upconverted to generate coherent tunable ultraviolet (UV) radiation for high-precision spectroscopy [19][20][21], e.g., at the fourth-harmonic wavelength (λ UV ) of 205-213 nm. This versatile high-performance laser-based system is especially useful for applications in the vacuum UV region where high peak power and narrow optical bandwidth are needed (e.g., in tens-of-ns pulses), for nonlinear-optical upconversion.…”

“…This versatile high-performance laser-based system is especially useful for applications in the vacuum UV region where high peak power and narrow optical bandwidth are needed (e.g., in tens-of-ns pulses), for nonlinear-optical upconversion. We have previously used this instrument, along with our distinctive coherent heterodyne-assisted pulsed spectroscopy (CHAPS) technique, for sub-Doppler TPE spectroscopy of gaseous atoms such as caesium (Cs) at ∼822.5 nm [20] and krypton (Kr) at ∼212.5 nm [21]. Our long-term objective is to improve the accuracy of a previous determination [22] of the absolute frequency for the 1 1 S → 2 1 S two-photon transition of helium (He), excited at a vacuum UV wavelength of ∼120 nm; this can provide a measure of the Lamb shift in ground-state He as a significant test of quantumelectrodynamic theory.…”