Laser-Based Metastable Krypton Generation

Abstract

We demonstrate the generation of metastable krypton in the long-lived 1s^{5} state using laser excitation. The atoms are excited through a two-photon absorption process into the 2p^{6} state using a pulsed optical parametric oscillator laser operating near 215 nm, after which the atoms decay quickly into the metastable state with a branching ratio of 75%. The interaction dynamics are modeled using density matrix formalism and, by combining this with experimental observations, we are able to calculate photoionization and two-photon absorption cross sections. When compared to traditional approaches to metastable production, this approach shows great potential for high-density metastable krypton production with minimal heating of the sample. Here, we show metastable production efficiencies of up to 2% per pulse. The new experimental results gained here, when combined with the density matrix model we have developed, suggest that fractional efficiencies up to 30% are possible under optimal conditions.

Single-Laser Krypton Tagging Velocimetry Investigation of Supersonic Air and N2 Boundary-Layer Flows over a Hollow Cylinder in a Shock Tube

“…1 (758.7 nm, transition B). Minor fluorescence contributions from transitions E and F, resulting from the recombination process (transition D) [81,82] Emission spectra are recorded to investigate the (2 + 1) REMPI process and extent of the ionization of the fluorescing Kr atoms during the write and read steps. The hypothesis is that if the spectra indicate transitions other than the 5p[1/2] 0 → 5s[3/2] o 1 (758.7 nm) transition, the Kr atoms are at least partially ionized.…”

“…The hypothesis is that if the spectra indicate transitions other than the 5p[1/2] 0 → 5s[3/2] o 1 (758.7 nm) transition, the Kr atoms are at least partially ionized. As a result of the partially ionized Kr population, the fluorescence observed during the read step would be the result of the spontaneous emission from the by-products of the Kr recombination process [81,82]. This process occurs at a longer timescale than spontaneous emission in the absence of ionization, thus enabling the tagged Kr atoms to be imaged with sufficient signal-to-noise ratio (SNR) during the read step without the need for a read laser.…”

Observation of dynamic Stark resonances in strong-field excitation

“…In recent years, there has been a demand for higher efficiency and cleaner sources of metastable atoms, encouraging all-optical methods of generation to be pursued. Examples include two-photon absorption [8] or methods employing UV lamps [9]. Strong-field excitation is also a promising technique.…”

Towards an Australian Atom-Trap Trace Analysis (ATTA) facility

“…A more efficient and cleaner metastable production technique could reduce measurement time, increase throughput, and allow measurement of smaller samples. While optical lamp-based excitation techniques have been considered before [2], here we explore two innovative laser excitation techniques: Multi-photon Excitation: We have experimentally measured two-photon transitions for optical excitation into the metastable level [3]. A two-photon excitation into krypton 2p6 state decays directly into the 1s5 metastable state with favourable (~75%) branching ratio, and we have demonstrated efficiencies of 2% per pulse, using a broad-bandwidth excitation source at 215nm.…”

“…A two-photon excitation into krypton 2p6 state decays directly into the 1s5 metastable state with favourable (~75%) branching ratio, and we have demonstrated efficiencies of 2% per pulse, using a broad-bandwidth excitation source at 215nm. Modelling suggests efficiencies up to 30% are possible under optimal conditions [3]. Frustrated Tunnel Ionization: We use a strong-field excitation technique [4,5] which takes advantage of a neutral exit channel available in the tunneling regime of strong-field ionization.…”