Development of High Contrast Coherent Anti-Stokes Raman Scattering (CARS) and Multiphoton Microscopy for Label-Free Biomolecular Imaging

Ph.DDOCTOR OF PHILOSOPH

7th International Conference on Nonlinear Vibrations, Localization and Energy Transfer: Extended Abstracts

International audienceThe purpose of our conference is more than ever to promote exchange and discussions between scientists from all around the world about the latest research developments in the area of nonlinear vibrations, with a particular emphasis on the concept of nonlinear normal modes and targeted energytransfer

Reflectivity of plasmas created by high-intensity, ultra-short laser pulses

Experiments were performed to characterize the creation and evolution of high-temperature (T{sub e}{approximately}100eV), high-density (n{sub e}>10{sup 22}cm{sup {minus}3}) plasmas created with intense ({approximately}10{sup 12}-10{sup 16}W/cm{sup 2}), ultra-short (130fs) laser pulses. The principle diagnostic was plasma reflectivity at optical wavelengths (614nm). An array of target materials (Al, Au, Si, SiO{sub 2}) with widely differing electronic properties tested plasma behavior over a large set of initial states. Time-integrated plasma reflectivity was measured as a function of laser intensity. Space- and time-resolved reflectivity, transmission and scatter were measured with a spatial resolution of {approximately}3{mu}m and a temporal resolution of 130fs. An amplified, mode-locked dye laser system was designed to produce {approximately}3.5mJ, {approximately}130fs laser pulses to create and nonintrusively probe the plasmas. Laser prepulse was carefully controlled to suppress preionization and give unambiguous, high-density plasma results. In metals (Al and Au), it is shown analytically that linear and nonlinear inverse Bremsstrahlung absorption, resonance absorption, and vacuum heating explain time-integrated reflectivity at intensities near 10{sup 16}W/cm{sup 2}. In the insulator, SiO{sub 2}, a non-equilibrium plasma reflectivity model using tunneling ionization, Helmholtz equations, and Drude conductivity agrees with time-integrated reflectivity measurements. Moreover, a comparison of ionization and Saha equilibration rates shows that plasma formed by intense, ultra-short pulses can exist with a transient, non-equilibrium distribution of ionization states. All targets are shown to approach a common reflectivity at intensities {approximately}10{sup 16}W/cm{sup 2}, indicating a material-independent state insensitive to atomic or solid-state details

Squeezing collective atomic spins with an optical resonator

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2011.This electronic version was submitted by the student author. The certified thesis is available in the Institute Archives and Special Collections.Cataloged from student submitted PDF version of thesis.Includes bibliographical references (p. 128-133).This thesis describes two methods of overcoming the standard quantum limit of signal-to-noise ratio in atomic precision measurements. In both methods, the interaction between an ultracold atomic ensemble and an optical resonator serves to entangle the atoms and deform the uncertainty distribution of the collective hyperfine spin so that it is narrower in some coordinate than would be possible if the atoms were uncorrelated. The first method uses the dispersive shift of the optical resonator's frequency by the atomic index of refraction to perform a quantum non-demolition measurement of the collective spin, projecting it into a squeezed state conditioned on the measurement outcome. The second method exploits the collective coupling of the atoms to the light field in the resonator to generate an effective interaction that entangles the atoms deterministically. Both methods are demonstrated experimentally, achieving metrologically relevant squeezing of 1.5(5) dB and 4.6(6) dB respectively, and simple analytical models, including the effects of scattering into free space, show that much greater squeezing is realistically achievable. To demonstrate the potential usefulness of such squeezing, a proof-of-principle atomic clock whose Allan variance decreases 2.8(3) three times faster than the standard quantum limit is also presented, together with a discussion of the conditions under which squeezing improves its performance.by Ian Daniel Leroux.Ph.D

Testing the Quantumness of Atom Trajectories

This thesis reports on a novel concept of state-dependent transport, which achieves an unprecedented control over the position of individual atoms in optical lattices. Utilizing this control I demonstrate an experimental violation of the Leggett Garg inequality, which rigorously excludes (i.e. falsifies) any explanation of quantum transport based on classical, well-defined trajectories. Furthermore, I demonstrate the generation of arbitrary low-entropy states of neutral atoms following a bottom-up approach by rearranging a dilute thermal ensemble into a predefined, ordered distribution in a one-dimensional optical lattice. Additionally, I probe two-particle quantum interference effects of two atom trajectories by realizing a microwave Hong-Ou-Mandel interferometer with massive particles, which are cooled into the vibrational ground state. The first part of this thesis reports on several new experimental tools and techniques: three-dimensional ground state cooling of single atoms, which are trapped in the combined potential of a polarization-synthesized optical lattice and a blue-detuned hollow dipole potential; A high-NA (0.92) objective lens achieving a diffraction limited resolution of 460 nm; and an improved super-resolution algorithm, which resolves the position of individual atoms in small clusters at high filling factors, even when each lattice site is occupied. The next part is devoted to the conceptually new optical-lattice technique that relies on a high-precision, high-bandwidth synthesis of light polarization. Polarization-synthesized optical lattices provide two fully controllable optical lattice potentials, each of them confining only atoms in either one of the two long-lived hyperfine states. By employing one lattice as the storage register and the other one as the shift register, I provide a proof of concept that selected regions of the periodic potential can be filled with one particle per site. In the following part I report on a stringent test of the non-classicality of the motion of a massive quantum particle, which propagates on a discrete lattice. Measuring temporal correlations of the position of single atoms performing a quantum walk, we observe a 6σ (standard deviation) violation of the Leggett-Garg inequality. The experiment is carried out using so-called ideal negative measurements – an essential requisite for any genuine Leggett-Garg test – which acquire information about the atom’s position while avoiding any direct interaction with it. This interaction-free measurement is based on our polarization-synthesized optical lattice, which allows us to directly probe the absence rather than the presence of atoms at a chosen lattice site. Beyond its fundamental aspect, I demonstrate the application of the Leggett-Garg correlation function as a witness of quantum superposition. The witness allows us to discriminate the quantumness of different types of walks spanning from merely classical to quantum dynamics and further to witness the decoherence of a quantum state. In the last experimental part I will discuss recent results on collisional losses due to inelastic collisions occurring at high two-atom densities and demonstrate a Hong-Ou-Mandel interference with massive particles. Our precise control over individual indistinguishable particles embodies a direct analogue of the original Hong-Ou-Mandel experiment. By carrying out a Monte Carlo analysis of our experimental data, I demonstrate a signature of the two-particle interference of two-atom trajectories with a statistical significance of 4σ. In the final part I will introduce several new experiments which can be realized with the tools and techniques developed in this thesis, spanning from the detection of topologically protected edge states to the prospect of building a one-million-operation quantum cellular automaton

NASA patent abstracts bibliography: A continuing bibliography. Section 1: Abstracts (supplement 34)

Abstracts are provided for 124 patents and patent applications entered into the NASA scientific and technical information systems during the period July 1988 through December 1988. Each entry consists of a citation, an abstract, and in most cases, a key illustration selected from the patent or patent application

Advanced control of ultrashort and high-power pulses in enhancement cavities

In the decade preceding this thesis, femtosecond enhancement cavities had emerged as a highly promising technology in the context of extreme ultraviolet light (XUV) sources for frequency comb metrology and attosecond physics. These applications require light of laser-like coherence, which can be provided by high-order harmonic generation (HHG), a highly nonlinear frequency conversion process driven by intense ultrashort laser pulses. The laser systems commonly used to drive HHG are limited to pulse repetition rates in the kilohertz range. In contrast, the enhancement of femtosecond pulses in passive optical cavities to average powers of many kilowatts delivers the necessary intensities even at repetition rates of tens to hundreds of megahertz. Achieving sufficient XUV flux with megahertz repetition rates would enable the extension of frequency comb metrology to the XUV, and dramatically reduce data acquisition times for experiments in attosecond physics. However, cavity-enhanced HHG comes with unique challenges, imposing cavity-related limitations to the power, peak intensity, and minimum duration of the driving pulses. In this thesis, several novel approaches to extending the capabilities of femtosecond enhancement cavities are presented. In a first experiment, we demonstrated the compensation of thermal lensing effects in enhancement cavities. Using intracavity Brewster plates, which also offer a robust solution for XUV output coupling in cavity-enhanced HHG setups, we gained control over the thermally-induced mode change at average powers of up to 160 kW. Subsequently, we investigated the effects of nonlinear phase modulations caused by ionization in an intracavity gas target, which is a prerequisite for HHG. We experimentally validated a numerical model of the plasma-cavity interaction, leading to a scaling law allowing for the layout of optimized cavity HHG systems, and a proposal for tailoring the spectral finesse of cavities to exploit the nonlinear phase modulation for intracavity pulse compression. In parallel, we worked on the design and characterization of highly reflective multilayer mirrors to optimize the cavity dispersion. Combining different mirrors with compatible spectral phase characteristics, we demonstrated enhancement cavities supporting waveform-stable pulses, and cavities supporting pulse durations approaching the few-cycle regime. These results represent vital technological developments towards the goal of isolated attosecond pulse generation with enhancement cavities. Finally, we applied the developed methods of dispersion control to design an enhancement cavity for intracavity pulse compression using self-phase modulation in a Brewster plate. Implementing a flexible locking scheme, we demonstrated for the first time the generation of temporal cavity solitons in free-space enhancement cavities. The temporal compression from 350 fs to 37 fs together with the spectrally tailored finesse resulted in a peak power enhancement factor of over 3000, significantly surpassing the enhancement in linear cavities supporting similar pulse durations. This intriguing result opens the door to a novel regime of nonlinear cavity operation, with potentially significant benefits to cavity-enhanced HHG. In addition, we proposed a concept for optomechanical cavity dumping, with the potential to aid efforts employing enhancement cavities for a new generation of high-pulse-energy lasers