Calculations are done to determine the specifications for an optical build up cavity which will produce the largest fraction of metastable krypton atoms using a two-photon transition with 215 nm light. Four different models are used from constant intensity and root-mean-square velocity to gaussian intensity and Maxwell speed distribution. A Ti:Sapphire laser is operated and internally stabilized. The theory of sub-Doppler spectroscopy is discussed.
Calculations are done to determine the specifications for an optical build up cavity which will produce the largest fraction of metastable krypton atoms using a two-photon transition with 215 nm light. Four different models are used from constant intensity and root-mean-square velocity to gaussian intensity and Maxwell speed distribution. A Ti:Sapphire laser is operated and internally stabilized. The theory of sub-Doppler spectroscopy is discussed.
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.
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 have realized the optical excitation of krypton to a metastable level with an efficiency as high as 23 using near-resonant 124-nm light produced by four-wave mixing in mercury vapor. Self-absorption in mercury is circumvented by adjusting the detuning and phase matching according to experimental and theoretical characterizations. Density-matrix calculations of the metastable krypton generation agree with the measured dependencies of the excitation efficiency, indicating pathways towards a further improvement. The obtained excitation efficiency, being one order of magnitude higher than that of previously demonstrated techniques, enables an extension of the metastable density regime for atomic physics applications, including magnetometry, atom lithography, and radioisotope dating.
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.
Nobel gases, with their closed electronic shells, require large energy to transfer the atoms from the electronic ground state to the first accessible excited state. For this reason, it is common to use various discharge sources to transfer atoms from the ground state into excited states, in particular into a long-lived metastable state for optical manipulation. There are specific applications, however, that would benefit from optical methods over discharge methods to produce metastable atoms. These include Atom Trap Trace Analysis and velocimetry/wind tunnel experiments, where a discharge source is impractical.