We have investigated a new scheme for excitation of the 5s, J = 2 metastable level of Kr (5s[3/2] J = 2 ) which can be readily extended to other rare gases. In the scheme, an ultraviolet (UV) lamp is used to create a population of Kr atoms in the 5s[3/2] J = 1 level in a gas cell. The excited atoms are then pumped to the 5p[3/2] J = 2 level, using 819 nm light from a Ti:sapphire laser, from which they decay to the metastable state with a branching ratio of 77%. We made two striking observations: (1) the laser power required to saturate the second step decreases markedly as a function of gas cell pressure, and (2) the UV photon flux is converted with very high efficiency (≈10%) to metastable atom flux. A Monte Carlo study of the scattering of UV photons in the cell reproduces the trends observed. The understanding achieved points to the design of a higher flux source of metastable atoms.
We have investigated a new scheme for excitation of the 5s, J = 2 metastable level of Kr (5s[3/2] J = 2 ) which can be readily extended to other rare gases. In the scheme, an ultraviolet (UV) lamp is used to create a population of Kr atoms in the 5s[3/2] J = 1 level in a gas cell. The excited atoms are then pumped to the 5p[3/2] J = 2 level, using 819 nm light from a Ti:sapphire laser, from which they decay to the metastable state with a branching ratio of 77%. We made two striking observations: (1) the laser power required to saturate the second step decreases markedly as a function of gas cell pressure, and (2) the UV photon flux is converted with very high efficiency (≈10%) to metastable atom flux. A Monte Carlo study of the scattering of UV photons in the cell reproduces the trends observed. The understanding achieved points to the design of a higher flux source of metastable atoms.
A room-temperature beam of krypton atoms in the metastable 5s[3/2]2 level is demonstrated via an optical excitation method. A Kr-discharge lamp is used to produce vacuum ultraviolet photons at 124 nm for the first-step excitation from the ground level 4p6 1S0 to the 5s[3/2]1 level. An 819 nm Ti:sapphire laser is used for the second-step excitation from 5s[3/2]1 to 5s[3/2]2 followed by a spontaneous decay to the 5s[3/2]2 metastable level. A metastable atomic beam with an angular flux density of 3 x 10(14) s(-1) sr(-1) is achieved at the total gas flow rate of 0.01 cm3/s at STP (or 3 x 10(17) at./s). The dependences of the flux on the gas flow rate, laser power, and lamp parameters are investigated.
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.
n this presentation, we discuss results from two separate bodies of work. In the first, we investigate all-optical excitation methods to produce metastable-state krypton. The high energies required to excite rare gases out of their ground state present a unique challenge in the context of laser experiments. Laser physics work with rare gases often relies on excitation within an RF discharge. All-optical excitation is a promising replacement for RF discharges, avoids problems caused by ion production and may eventually allow for higher efficiencies. We examine three separate methods of all-optical metastable-state production: using an ArF excimer laser, using the third harmonic of the Jefferson Lab free-electron laser (FEL), and using a commercially available UV lamp. In the second body of work, we perform photoassociation spectroscopy in an ultracold, heteronuclear Rb + Ar* system. Photoassociation is a method that may be used to both 1) produce ultracold molecules, and 2) perform high-resolution spectroscopy on excited molecular states. Most work within the field has been performed within all alkali-metal systems. We examine a unique noble gas–alkali system within a dual species magneto-optical trap. We have performed a comprehensive search for evidence of excitation to molecular levels of RbAr. We illuminate atom pairs with a photoassociation laser in a spectral region detuned a few GHz below an atomic asymptote of argon, analogous to previous work in the homo-nuclear argon or krypton systems. We discuss our methodology and findings. We conclude with a discussion of how our results may be applied to future spectroscopic searches
Optically pumped alkali vapor lasers are currently being developed in several laboratories. The objective is to construct high-powered lasers that also exhibit excellent beam quality. Considerable progress has been made, but there are technical challenges associated with the reactivity of the metal atoms. Rare gas atoms (Rg) excited to the np(5)(n+1)s (3)P(2) configuration are metastable and have spectral properties that are closely similar to those of the alkali metals. In principle, optically pumped lasers could be constructed using excitation of the np(5)(n+1)p←np(5)(n+1)s transitions. We have demonstrated this potential by observing gain and lasing for optically pumped Ar(*), Kr(*) and Xe(*). Three-level lasing schemes were used, with He or Ar as the collisional energy transfer agent that established the population inversion. These laser systems have the advantage of using inert reagents that are gases at room temperature.
Radioisotopes that break down at a constant rate over time through radioactive decay allow scientists to understand the development of geological and anthropological history by dating samples that contain such isotopes. While many techniques exist to measure the age of a sample, in this thesis we explore the possibility of enhancing the atom trap trace analysis (ATTA) method, which has made significant strides in the area of ultra-sensitive radioisotope detection, especially with the use of metastable noble gas radionuclides. A metastable atom is an atom in a stable, long-lived (>1 ms) excited state. Noble gases have the longest metastable lifetimes, which combined with their geochemical inertness, make them ideal candidates for geological and environmental radiometric techniques. The production of metastable noble gases for this purpose has traditionally relied on discharge sources, but this method suffers from important drawbacks such as high levels of crosscontamination and poor excitation efficiencies. In an effort to overcome these drawbacks, the method described in this work presents a new platform for implementing, characterising and comparing purely laser-based production of metastable noble gases. In the first part of this thesis, we present both state-of-the-art experimental results in the purely laser-based generation of metastable krypton atoms, and a physically realistic simulation with good agreement with our experimental results. Our calculation of the twophoton absorption cross section for krypton (to a metastable-generating excited state) using 215nm deep ultraviolet (DUV) laser radiation, obtained by fitting with theory, confirms that high metastable production efficiencies are possible with laser-based techniques. In addition to this parameter, the branching ratio and photoionisation rate from the excited state are calculated and agree with the literature. In the second part, we present the experimental progress to date for a brand new method of manipulating metastable noble gas atoms using a two-stage approach of metastable production then trapping via a magneto-optical trap (MOT). While the results are limited due to experimental difficulties, they are complemented by a physically realistic 3D simulation based on the Monte Carlo method. This simulation suggests that the production and trapping of metastable noble gases is feasible without the use of a discharge source, a Zeeman slower, and even a secondary excitation chamber. However, the loading rate for such a MOT is not sufficient for ATTA measurements without drastic changes in the experimental configuration. In the final part, we propose a next-generation ATTA system based on stimulated rapid adiabatic passage (STIRAP) to transfer noble gas atoms to their metastable state with near 100% efficiency. This technique for the generation of metastable noble gases would be purely laser-based and would compete with the loading rates of conventional production techniques, while avoiding their deleterious effects. We conclude by identifying limits of laser-based techniques and explore approaches to overcome them.
Pulsed lasing from optically pumped rare gas metastable atoms (Ne, Ar, Kr, and Xe) has been demonstrated previously. The laser relies on a three-level scheme, which involves the (n+1)p[5/2](3) and (n+1)p[1/2](1) states from the np(5)(n+1)p electronic configuration and the metastable (n+1)s[3/2](2) level of the np(5)(n+1)s configuration (Racah notation). Population inversions were achieved using relaxation from ((n+1)p[5/2](3) to (n+1)p[1/2](1) induced by collisions with helium or argon at pressures near 1 atm. Pulsed lasing was easily achieved using the high instantaneous pump intensities provided by a pulsed optical parametric oscillator excitation laser. In the present study we examine the potential for the development of a continuous wave (CW) optically pumped Ar laser. We report lasing of the 4p[1/2](1)→4s[3/2](2) (912.547 nm) transition following CW diode laser excitation of the 4p[5/2](3)←4s[3/2](2) line (811.754 nm). A pulsed discharge was used to generate Ar 4s[3/2](2), and the time-resolved lasing kinetics provide insights concerning the radiative and collisional relaxation processes.