Holography

Holography - Basic Principles and Contemporary Applications is a collection of fifteen chapters, describing the basic principles of holography and some recent innovative developments in the field. The book is divided into three sections. The first, Understanding Holography, presents the principles of hologram recording illustrated with practical examples. A comprehensive review of diffraction in volume gratings and holograms is also presented. The second section, Contemporary Holographic Applications, is concerned with advanced applications of holography including sensors, holographic gratings, white-light viewable holographic stereograms. The third section of the book Digital Holography is devoted to digital hologram coding and digital holographic microscopy

Ultrafast Broadband Terahertz Spectroscopy

This dissertation centers on broadband terahertz spectroscopy and is arranged in four main sections. In the first section, we describe terahertz generation from a two-color laser air breakdown plasma. This is modeled with a plasma current that includes plasma density and dispersion in propagation. The terahertz spatial profile has a ring-like structure with a frequency dependent radius. Parameters for optimal terahertz generation are also presented. The next two sections discuss broadband terahertz detection techniques: optically biased coherent detection and electro-absorption in a semiconductor. The subject of the fourth section is terahertz imaging with electroabsorption. Optically biased coherent detection is distinguished from air-breakdown coherent detection by replacing the electrical bias for an optical field. The importance of phase control in this technique is demonstrated. In addition, we found the terahertz-induced second harmonic to be spectrally delay-dependent. This is due to the phase matching condition and is discussed in detail. Terahertz-induced electro-absorption is performed in GaAs/AlGaAs multiple double quantum wells and an AlGaAs bulk semiconductor. To the best of the author\u27s knowledge, this is the first demonstration of large modulation induced by a single cycle terahertz pulse in such structures. The underlying mechanism is identified as the Franz-Keldysh effect that has been successfully modeled in both the temporal and spectral regimes. Terahertz imaging of the plasma profile is accomplished with electro-absorption in these structures. The observed ring pattern is reproduced with the model described in the first section of this dissertation. Terahertz raster scan imaging of a large object is also presented

Program Annual Technology Report: Physics of the Cosmos Program Office

From ancient times, humans have looked up at the night sky and wondered: Are we alone? How did the universe come to be? How does the universe work? PCOS focuses on that last question. Scientists investigating this broad theme use the universe as their laboratory, investigating its fundamental laws and properties. They test Einsteins General Theory of Relativity to see if our current understanding of space-time is borne out by observations. They examine the behavior of the most extreme environments supermassive black holes, active galactic nuclei, and others and the farthest reaches of the universe, to expand our understanding. With instruments sensitive across the spectrum, from radio, through infrared (IR), visible light, ultraviolet (UV), to X rays and gamma rays, as well as gravitational waves (GWs), they peer across billions of light-years, observing echoes of events that occurred instants after the Big Bang. Last year, the LISA Pathfinder (LPF) mission exceeded expectations in proving the maturity of technologies needed for the Laser Interferometer Space Antenna (LISA) mission, and the Laser Interferometer Gravitational-Wave Observatory (LIGO) recorded the first direct measurements of long-theorized GWs. Another surprising recent discovery is that the universe is expanding at an ever-accelerating rate, the first hint of so-called dark energy, estimated to account for 75% of mass-energy in the universe. Dark matter, so called because we can only observe its effects on regular matter, is thought to account for another20%, leaving only 5% for regular matter and energy. Scientists now also search for special polarization in the cosmic microwave background to support the notion that in the split-second after the Big Bang, the universe inflated faster than the speed of light! The most exciting aspect of this grand enterprise today is the extraordinary rate at which we can harness technologies to enable these key discoveries

Optics and Fluid Dynamics Department annual progress report for 2002

research within three scientific programmes: (1) laser systems and optical materials, (2) optical diagnostics and information processing and (3) plasma and fluid dynamics. The department has core competences in: optical sensors, optical materials, optical storage, biophotonics, numerical modelling and information processing, non-linear dynamics and fusion plasma physics. The research is supported by several EU programmes, including EURATOM, by Danish research councils and by industry. A summary of the activities in 2002 is presented. ISBN 87-550-3197-8 (Internet

Terahertz for subsurface imaging and metrology applications

In the area of metrology and non-destructive testing, Terahertz wavelengths have been widely researched and used. However, the lack of 2D detectors working at room temperature and high power sources prevent the widespread application of Terahertz in industry. In that context, research on the development of new Terahertz equipment is moving at a fast pace. Within the scope of this thesis, applications of newly developed Terahertz technologies were explored using the scanning of single point detectors with the objective to establish the feasibility for their full-field applications in readiness for future 2D detectors. For the first time, a frequency tuneable, all-optical Terahertz source was implemented in multi-wavelength interferometry to overcome one wavelength ambiguity in precise thickness/distance measurements with sub-millimetre resolution. Phase-shifting digital holography is another interferometry technique which allows us to reconstruct not only the amplitude of one object, but also the phase and the depth of it, using existing mathematical algorithms. Digital holography was performed successfully at Terahertz wavelengths using a multiplier/mixer Terahertz source coupled with a single point pyroelectric detector for the applications of non-destructive testing and depth measurements. The novelty is that the phase-stepping technique for digital holography was implemented in THz frequencies for the first time to remove unwanted terms in the reconstructed image in order to improve image quality compare to conventional holography. In the current experiments, recording time for one set of phase-shifting holograms (4 holograms for 4 phase-steps algorithm) was 6 hours. When the technology is ready for 2D detectors, recording time of holograms could be reduced considerably, and the technique will play an important role in full-field applications in industry metrology and/or non-destructive testing and evaluation.EPSR

Fully integrated transducer platform with cavity optomechanical readout

Research and development of transducers based on cavity optomechanics is a topic of high interest particularly because these transducers enable measurement of mechanical motion down to the fundamental limit of precision imposed by quantum mechanics. The development of an on-chip cavity optomechanical transducer platform that combines high bandwidth and sensitivity near the standard quantum limit with compactness, robustness, small size, and potential for low cost batch fabrication inherent in MEMS is demonstrated as a proof of concept study. Design, fabrication and characterization of fully integrated and fiber pigtailed transducers is presented. The devices combine high sensitivity (0.14 - 40 fm·Hz^(-1/2), high bandwidth optomechanical readout and built-in thermal and electrostatic actuation. It is implemented by a double-side wafer-scale microfabrication process combining one e-beam, six stepper, and three contact mask aligner lithography steps. The SiN probes can be actuated using an electrical signal supplied to an integrated thermal or electrostatic actuator. The probe is evanescently coupled to a high-Q (10^5 - 2 x 10^6) optical whispering gallery mode of the optical microdisk cavity and the motion is detected by measuring the resonance frequency shift of the optical cavity mode. The actuator can be used to dynamically move the probe as well as to tune the distance between the cantilever and the optical cavity, to change the sensitivity and range of measurement of the cantilever. One side of the probe overhangs the edge of the chip, where it can be easily coupled to a variety of off-chip samples and physical systems of interest. The modular design of the transducer allows for parallelization, which enables the possibility of sensor arrays for simultaneous detection of multiple forces or other physical properties. Parallelization is shown on a 2x1 array, which can be easily extended to larger array architectures. The application of the probe arrays and single probes in a commercial scanning probe microscope is shown. In addition the flexibility of this transducer approach is demonstrated with membrane transducers and acceleration sensors. The performance of all presented transducers is studied, focusing on displacement sensitivity, frequency stability and readout gain tuning.Forschung und Entwicklung von Wandlern basierend auf kavität- optomechanischen Elementen ist ein Forschungsgebiet von hohem Interesse. Sie kombiniert hohe Bandbreiten und Empfindlichkeit nahe dem Standardquantumlimit mit Kompaktheit, Robustheit, kleinen Abmessungen und dem Potential für eine wirtschaftliche Massenproduktion systemimmanent bei mikroelektromechanischen Systemen. Vollintegrierte Wandler erlauben demnach Bewegungsmessungen bis hin zum fundamentalen Quantenlimit. In dieser Arbeit werden Design, Herstellung und Charakterisierung eines vollintegrierten und glasfasergekoppelten Wandlers in einer Machbarkeitsstudie dargestellt. Das System kombiniert hohe Verschiebungsauflösungen 0.14 - 40 fm· Hz^(-1/2), optomechanische Detektion mit hoher Bandbreite und eine eingebaute thermische und elektrostatische Anregung. Die Herstellung erfolgt in einem doppelseitigen mikro- und nanotechnischen Fertigungsverfahren auf Waferbasis, in einer Kombination aus einem Elektronenstrahllithographieschritt, sechs Projektionslithographieschritten und drei Kontaktlithographie Schritten. Die Siliziumnitrid-Sonden können mittels eines elektrischen Signals, angelegt an den integrierten thermischen oder elektrostatischen Aktuator, angeregt werden. Sie sind optisch über das evanecente Feld mit einer optischen Kavität hoher Güte (10^5 - 2 x 10^6) gekoppelt. Die Bewegung der Sonde wird detektiert über eine Veränderung der Resonanzfrequenz der Kavität. Die eingebauten Aktuatoren ermöglichen die Einstellung des Abstandes zwischen Sonde und optischer Kavität, welche die Einstellung der Sensitivität ermöglicht. Eine Seite der Sonde steht über die Kante des Siliziumchips, um die Kopplung mit einer Vielzahl von Proben und physikalischen Systemen zu erlauben. Die modulare Bauweise des Wandlers schafft die Grundlage zur Parallelisierung der Sonden für die gleichzeitige Messung mehrerer Kräfte oder physikalischer Eigenschaften. Die Parallelisierung wird in dieser Arbeit am Beispiel eines 2x1 Array gezeigt, welche mit geringem Aufwand auf größere Arrayarchitekturen angepasst werden kann. Zur Demonstration der Funktion von Einzelsonden und Sondenarrays, wird die Sondenanwendung in der Rasterkraftmikroskopie präsentiert. Des Weiteren wird die Flexibilität der Wandlerbauweise an der Herstellung von Membrane- und Beschleunigungswandlern belegt. Das Verhalten aller hergestellten Wandler wird hinsichtlich der Bewegungsempfindlichkeit, Frequenzstabilität, und Einstellbarkeit der Auslesung analysiert

Enabling Real-Time Terahertz Imaging With Advanced Optics and Computational Imaging

La bande des térahertz est une région particulière du spectre électromagnétique comprenant les fréquences entre 0.1 THz à 10 THz, pour des longueurs d’onde respectives de 3 mm à 30 um. Malgré tout l’intérêt que cette région a suscité au cours de la dernière décennie, de grands obstacles demeurent pour une application plus généralisée de la radiation THz dans les applications d’imagerie. Cette thèse aborde le problème du temps d’acquisition d’une image THz. Notre objectif principal sera de développer des technologies et techniques pour permettre l’imagerie THz en temps réel. Nous débutons cette thèse avec une revue de littérature approfondie sur le sujet de l’imagerie THz en temps réel. Cette revue commence par énumérer plusieurs sources et détecteurs THz qui peuvent immédiatement être utilisés en imagerie THz. Nous détaillons par la suite plusieurs modalités d’imagerie développés au cours des dernières années : 1) Imagerie THz en transmission, en réflexion et de conductivité, 2) imagerie THz pulsée, 3) imagerie THz par tomographie computationnelle et 4) imagerie THz en champ proche. Nous discutons par la suite plus en détail à propos de technologies habilitantes pour l’imagerie THz en temps réel. Pour cela, nous couvrons trois différents axes de recherche développés en littérature : 1)Imagerie en temps réel de spectroscopie THz dans le domaine du temps, 2) caméras THz et 3) imagerie en temps réel avec détecteur à pixel unique. Nous présentons ensuite le système d’imagerie que nous avons développé pour les démonstrations expérimentales de cette thèse. Ce système est basé sur la spectroscopie THz en temps réel et permet donc d’obtenir des images hyperspectrales en amplitude et en phase. Il utilise des antennes photoconductrices pour l’émission et la détection de la radiation THz. En outre, le détecteur est fibré, ce qui permet de le déplacer spatialement pour construire des images. Nous couvrons aussi brièvement plusieurs techniques de fabrication avancées que nous avons utilisées : impression 3D par filament, stéréolithographie, machinage CNC, gravure/découpe laser et transfert de métal par toner. Nous portons ensuite notre attention à l’objectif principal de cette thèse à travers trois démonstrations distinctes. Premièrement, nous concevons des composants THz à faibles pertes en utilisant des matériaux poreux. L’absence de détecteurs THz ultra-sensibles implique que les pertes encourues dans un système d’imagerie sont hautement indésirables. En effet, un moyennage temporel est généralement fait pour extraire de faibles signaux THz sévèrement enfouis sous le bruit technique. Ceci a pour impact de diminuer le nombre d’images à la seconde. ----------Abstract The terahertz band is a region of the electromagnetic spectrum comprising frequencies between 0.1 THz to 10 THz for respective wavelengths of 3 mm to 30 um. Despite all the interest and potential generated in the past decade for applications of this spectral band, there are still major hurdles impeding a wider use of THz radiation for imaging. This thesis addresses the problem of image acquisition time. Our main objective is to develop technologies and techniques to achieve real-time THz imaging. We start this thesis with a comprehensive review of the scientific literature on the topic of realtime THz imaging. This review begins by listing some off-the-shelf THz sources and detectors that could be readily used in THz imaging. We then detail some key imaging modalities developed in the past years: 1) THz transmission, reflection and conductivity imaging, 2) THz pulsed imaging, 3) THz computed tomography, and 4) THz near-field imaging. We then discuss practical enabling technologies for real-time THz imaging: 1) Real-time THz timedomain spectroscopy imaging, 2) THz cameras, and 3) real-time THz single-pixel imaging. We then present our fiber-coupled THz time-domain spectroscopy imaging setup. This system is used throughout the thesis for experimental demonstrations. We also briefly overview many advanced fabrication techniques that we have used, namely fused deposition modeling,stereolithography, CNC machining, laser cutting/engraving and metal transfer using toner. We then turn to the main objective of this thesis with three distinct demonstrations. First, we design low-loss THz components using porous media. The losses incurred in the imaging system are highly undesirable due to the lack of sensitive THz detectors. Indeed, time averaging is generally performed in order to retrieve THz signals severely buried under noise,which in return reduce the framerate. We propose to use low-refractive index subwavelength inclusions (air holes) in a solid dielectric material to build optical components. We show that these components have smaller losses than their all-solid counterparts with otherwise identical properties. We fabricate a planar porous lens and an orbital angular momentum phase plate, and we use our imaging system to characterize their effects on the THz beam. Second, we demonstrate a spectral encoding technique to significantly reduce the required number of measurements to reconstruct a THz image in a single-pixel detection scheme

Field resolving spectrometer for mid-infrared molecular spectroscopy

The interrogation of molecular samples with broadband mid-infrared (MIR) radiation results in highly specific “vibrational fingerprints,” containing a wealth of information on molecular structure and composition. This renders vibrational spectroscopy a powerful and versatile tool for applications ranging from fundamental science to the life sciences and to industrial applications. Conventional MIR spectroscopic techniques face severe limitations in detection sensitivity, in particular due to the poor coherence properties of common MIR sources as well as to the moderate detectivity and dynamic range of broadband MIR detectors. The research reported in this thesis has addressed the quest for novel routes towards tapping the potential of MIR spectral fingerprinting, harnessing modern, high-power femtosecond laser technology. The first part of the work reports the construction of octave-spanning, coherent femtosecond MIR sources, employing state-of-the-art 100-W-average-power-level thin-disk Yb:YAG modelocked oscillators. We demonstrated ultrabroadband coherent MIR sources with a brilliance exceeding that of MIR beamlines at 3rd-generation synchrotrons, and found that pulses emerging via intra-pulse difference frequency generation offer superior (and unparalleled) optical-waveform stability as compared to standard optical-parametric amplification. The temporal confinement of broadband MIR radiation to trains of sub-100-femtosecond pulses, together with field-resolved detection via electro-optic sampling (EOS) affords detection of the molecular fingerprint signal in the near-infrared region, where highly-efficient, high-dynamic-range detectors exist. Optimized EOS detection enabled a linear response over an intensity dynamic range of 150 dB at a central wavelength of 8.6 µm. This exceeds the previous state of the art by a large margin and has paved the way to high-signal-to-noise-ratio transmission measurements of aqueous biological samples like living cells and tissue. The waveform stability of the mid-infrared pulses plays a crucial role for real-life field-resolved spectroscopy measurements, and is of paramount importance for precision-metrological applications. In the second part of this thesis, high-quantum-efficiency EOS was employed for precision measurements of waveform jitter, evaluated for millions of pulses. This study demonstrated few-attosecond temporal jitter in the 1-Hz-to-0.625-MHz band, between the centre of mass of the driving near-infrared pulses, and individual field zero-crossings of the emerging, broadband mid-infrared field. This confirms the outstanding waveform stability achievable with second-order parametric processes with an order-of-magnitude improved accuracy compared to previous measurements. Furthermore, chirping the MIR pulse revealed attosecond-level optical-frequency-dependent waveform jitter, whose dynamics were quantitatively traced back to excessive intensity noise of the mode-locked oscillator. Thus, this study validated EOS as a broadband (both in the radio-frequency and in the optical domain), high-sensitivity measurement technique for the dynamics of optical waveforms beyond the standard, optical-spectrum-integrating carrier-envelope phase model. The instrument developed during this thesis was utilized for the first highly sensitive field-resolved measurements in the MIR molecular fingerprint region. It enabled the detection of molecular concentrations spanning 5 orders of magnitude down to 200-ng/mL in aqueous solutions and the examination of living biological systems with a thickness of up to 0.2 mm. Currently, the instrument is being used for the first large-scale studies on disease recognition based on vibrational fingerprinting of human blood serum. The implementation of intra-scan referencing, successfully carried out in the last weeks of this doctoral work, together with fast-scanning techniques and the extension of the MIR spectral bandwidth which are underway at our laboratory, promise to extend the technology pioneered in this thesis to new levels of sensitivity and reproducibility in vibrational spectroscopy. In addition to directly benefitting analytical applications, these developments are likely to afford novel insights into light-matter interactions