Optical thin film measurement by interferometric fringe projection and fluorescence stimulated emission

The introduction of a new technique for metrology of thin liquid films to give both the profile of the exterior surface and information on the thickness of the film is the main focus of this research. The proposed approach is based on the use of fringe projection system with a narrow band laser illumination and a high concentration of fluorescent dye dissolved in the fluid in order to generate fluorescence emission from minimum thickness of the film (i.e. the top few microns). The method relies on calculation of an interference phase term and the modulation depth of the fringes created by means of a twin fibre configuration. The characterisation of candidate fluorescent dyes in terms of absorption, related to the depth of penetration of the incident light into the dye and their fluorescence emission efficiency is presented and their application in full field imaging experiments is evaluated. A strong focus of the technique proposed is its flexibility and versatility allowing its extension to phase stepping techniques applied to determine the (fringe) phase map from static and dynamic fluids. Some experiments are carried out using the best dye solution in terms of fluorescence emission and light depth penetration. On the basis of the phase-height relationship achieved during the calibration process, the proposed measurement system is applied for the shape measurement of some static fluids. The profile of the exterior surface of these fluids is investigated by means of phasestepping technique and the resolution of the measurements is estimated. Furthermore a flow rig set-up based on inclined system (gravity assisted) is presented in order to test the shape measurement system in presence of real liquid flows. Different liquid flow thicknesses are processed and analysed. Example data will be included from some fluid films of known geometry in order to validate the method

High-resolution saturation spectroscopy of singly-ionized iron with a pulsed uv laser

We describe the design and realization of a scheme for uv laser spectroscopy of singly-ionized iron (Fe II) with very high resolution. A buffer-gas cooled laser ablation source is used to provide a plasma close to room temperature with a high density of Fe II. We combine this with a scheme for pulsed-laser saturation spectroscopy to yield sub-Doppler resolution. In a demonstration experiment, we have examined an Fe II transition near 260 nm, attaining a linewidth of about 250 MHz. The method is well-suited to measuring transition frequencies and hyperfine structure. It could also be used to measure small isotope shifts in isotope-enriched samples.Comment: 9 pages, 5 figures, updated Fig. 3. For submission to J. Phys.

Frequency-comb-referenced molecular spectroscopy in the mid-infrared region

A simple method for absolute frequency measurements of molecular transitions in the mid-infrared region is reported. The method is based on a cw singly-resonant optical parametric oscillator (SRO), which is tunable from 3.2 to 3.45 µm. The mid- infrared frequency of the SRO is referenced to an optical frequency comb through its pump and signal beams. Sub-Doppler spectroscopy and absolute frequency measurement of the P(7) transition of the ν3 band of CH4 are demonstrated.Peer reviewe

Applications of Nonlinear Optical Gain Mechanisms from Phonon and Atomic Vapor Interactions

There are many methods to achieve optical gain for laser applications; such methods have been used to make improved spectroscopy and microscopy apparatus. In particular, gain from acoustic and atomic interactions has attained much interest, as is evident in the literature. In this work, we report the results of several experiments involving nonlinear Brillouin scattering and three-level gain in rubidium vapor. Brillouin scattering, both spontaneous and stimulated, in principle result from the scattering of light off of acoustic waves in a medium. While both spontaneous and stimulated Brillouin scattering have been applied to spectroscopy of various samples, from condensed matter to gases, only spontaneous Brillouin scattering has been used for microscopy purposes. We report our result from several proof-of-principle experiments in which stimulated Brillouin scattering and impulsive stimulated Brillouin scattering were applied to microscopic purposes for the first time. We show the advantages these methods afford over spontaneous Brillouin scattering and make a statistical comparison between them. There are also many ways to achieve gain in atomic vapors. Using a setup similar to the stimulated Brillouin scattering setup we performed gain in a three-level Λ system in warm rubidium vapor. To our knowledge, this is the first time this three-level analog of Mollow’s two-level system with Doppler broadening has been experimentally investigated. Our results show about 0.12% gain in the probe beam. This work, and extensions of it, should provide additional methods of performing spectroscopy and microscopy in various materials from atoms to bulk matter

Atom Trapping and Spectroscopy in Cavity-Generated Optical Potentials.

In this thesis I study atom trapping in GHz-deep optical lattices, generated by an in-vacuum near-concentric optical cavity at 1064~nm, to perform experiments on cold Rydberg atoms. In contemporary atomic physics, cold Rydberg atoms are widely used due to their high sensitivity to static and ac fields, as well as to their unusual collision properties. In my research, I intend to study the response of such atoms to GHz-deep optical traps. In the atom preparation procedure, the deep optical-lattice trap adiabatically compresses the cold rubidium atom sample within the lattice wells, where the atoms experience light shifts of several GHz. The deep optical-lattice trap allows me to perform several spectroscopy experiments which have not yet been done. An experimental challenge that had to be overcome was the realization of GHz-deep light shift traps (which are highly unusual in the field). The design of the cavity experiment also allows a fast experimental repetition rate (which is advantageous in spectroscopy experiments), a large atomic number density, and cold-atom samples with a highly elongated aspect ratio. A near-concentric cavity is the only type of stable two-mirror cavity that has a focus at the cavity center. This configuration not only provides high laser intensity at the cavity center, but also nearly perfect three-dimensional optical trapping potential based on the cavity's non-degenerate cavity modes. The cavity-generated optical trapping potentials offer a platform for deep ponderomotive Rydberg spectroscopy which would be otherwise very difficult in a conventional optical-lattice experimental setup.PhDPhysicsUniversity of Michigan, Horace H. Rackham School of Graduate Studieshttp://deepblue.lib.umich.edu/bitstream/2027.42/113459/1/yjhih_1.pd