Digital holography with ultimate sensitivity

We propose a variant of the heterodyne holography scheme that combines the properties of off-axis and phase-shifting holography. This scheme makes it possible to filter off numerically the zero-order image alias and the technical noise of the reference. It is then possible to record and reconstruct holographic images at an extremely low signal level. We show experimentally that the sensitivity of the method is limited only by the quantum nature of photons.Comment: 3 page

Cavity enhanced detection of cold molecules

Cold quantum gases are versatile tools not only to investigate quantum many-body physics and ultracold chemistry, but also for testing fundamental theories. Many degenerate quantum gases, however, consist of atoms and provide only short-range interactions between different particles limiting research opportunities. Hence, shortly after the production of the first atomic gases an interest arose in ensembles of cold polar molecules that exhibit adjustable long-range anisotropic dipole-dipole interactions to expand research fields further. Loading such a molecular cloud into an optical lattice provides an excellent experimental control regarding particle-particle interactions and to simulate condensed matter physics. Experiments with cold quantum gases require imaging techniques to determine properties like the number of atoms and molecules or the position of single particles. For atomic ensembles, absorption or fluorescence techniques are often utilised since atoms usually provide closed cycling transitions allowing to scatter a large number of photons for the imaging signal. The internal level structure of molecules, though, is more complex compared to atoms due to additional rovibrational states and many molecules do not provide closed cycling transitions. For these molecules new imaging techniques need to be developed. In the first part of the thesis a theoretical background of the imaging technique is provided, starting with a classical approach. The advantages of a classical theory are an intuitive understanding of the detection method and an applicability to spherical nanoparticles, which can then be utilised as test objects for the proposed imaging scheme. The resolution capability of the detection technique is discussed and the important role of small cavity waists for high resolutions is highlighted. In a next step, a full quantum mechanical approach is presented and compared to the classical theory. It is shown that both theories are equivalent except for vacuum fluctuations, a pure quantum physical effect important to determine quantum noise correctly. After introducing theoretical backgrounds, cavity geometries suitable for the detection of molecules are discussed. Properties, directly important for the imaging process, e.\;g. waist, mode number and linewidth, and technical aspects like misalignment sensitivity are taken into account. A simultaneous optimisation of all these properties is not possible since they are partially contradicting each other. However, a balance between these different aspects is found. Two cavity geometrics, feasible for imaging NaK molecules, a hemispherical resonator and a concentric cavity are proposed. Finally, an experimental setup to demonstrate the general feasibility of the imaging technique is developed. Titania and silver are identified as materials for nanoparticles best suited to imitate NaK molecules. Imaging resonators are designed and an alignment procedure for these cavities is presented

On the Digital Holographic Interferometry of Fibrous Material, I. Optical Properties of Polymer and Optical Fibers

The digital holographic interferometry (DHI) was utilized for investigating the optical properties of polymer and optical fibers. The samples investigated here were polyvinylidene fluoride (PVDF) polymer fiber and graded-index (GRIN) optical fiber. The phase shifting Mach-Zehnder interferometer was used to obtain five phase-shifted holograms, in which the phase difference between two successive holograms is pi/2, for each fiber sample. These holograms were recorded using a CCD camera and were combined to gain a complex wavefield, which was numerically reconstructed using the convolution approach into amplitude and phase distributions. The reconstructed phase distribution was used to determine the refractive index, birefringence and refractive index profile of the studied samples. The mean refractive index has been measured with accuracy up to 4 {\times} 10-4. The main advantage of DHI is to overcome the manual focusing limitations by means of the numerical focusing. The results showed accurate measurements of the optical properties of fibers.Comment: abstract, reference

Noise and aliases in off-axis and phase-shifting holography

We have compared the respective efficiencies of off-axis and phase-shifting holography in terms of noise and aliases removal. The comparison is made by analyzing holograms of an USAF target backlit with laser illumination, recorded with a charge-coupled device camera. We show that it is essential to remove the LO beam noise, especially at low illumination levels

Solid-State Excitation Laser for Laser-Ultrasonics

The inspection speed of laser-ultrasonics compared with conventional ultrasonic testing is limited by the pulse repetition rate of the excitation laser. The maximum pulse repetition rate reported up to now for CO2-lasers, which are presently used for nearly all systems, is in the range of 400 Hz. In this paper a new approach based on a diode-pumped solid-state laser is discussed, which is currently being developed. This new excitation laser is designed for a repetition rate of 1 kHz and will operate at a mid-IR wavelength of 3.3 m. The higher repeti-tion rate enables a higher inspection speed, whereas the mid-IR wavelength anticipates a better coupling efficiency. The total power for pumping the laser crystals is transported via flexible optical fibres to the compact laser head, thus allowing operation on a robot arm. The laser head consists of a master oscillator feeding several lines of power amplifiers and in-cludes nonlinear optical wavelength conversion by an optical parametric process. It is char-acterized by a modular construction which provides optimal conditions for operation at high average power as well as for easy maintenance. These features will enable building reliable, long-lived, rugged, smart laser ultrasonic systems in futur

Time resolved digital holography applied to droplets fragmentation by shockwave

International audienceDroplets atomization by shockwave can occur in different issues commonly encountered in the industry such as leak, tank leakage or triple aggression (high speed impact, rupture and surrounded secondary explosion) of tanks. For the last case, shockwave can interact with liquid jets of drops and propagates the liquid far away from the container zone. Very fine secondary droplets can be produced in the worst case of atomization. These small particles can generate secondary effects like explosion in case of petrol derivatives in fire or toxic effects in case of direct breathing. High speed imaging is well suited to study transient phenomenon like explosions and shockwave. A dedicated shockwave generator has been designed to cope with interferometric measurement on holographic bench. This demonstrator is made of thick plastic tubes. The high pressure chamber is isolated from the guiding tube by domestic aluminum foils, the thickness and number of which drive the pressure rupture. Previous works have been carried on by time resolved shadowgraphy to characterize generated shockwave at the guiding tube outlet. This paper deals with time resolved digital holography to perform higher accuracy measurements and of course to reach 3D reconstruction of the whole phenomenon. Lensless in-line digital holography is carried on to improve the stability of the holographic set-up. Different Phantom high speed cameras have been tested as recording sensors, following pixel pitch, pixel size and of course the maximal throughput, from 7kfps (frame per second) up to 26kfps at full 1Mpixel resolution. Different regimes of droplet trains and droplet sizes have been tested. This has also been carried on for different liquids to show the effect of the physico-chemical properties of the liquid subjected to shockwave

Imaging Gold Nanoparticles in Living Cells Environments using Heterodyne Digital Holographic Microscopy

This paper describes an imaging microscopic technique based on heterodyne digital holography where subwavelength-sized gold colloids can be imaged in cell environment. Surface cellular receptors of 3T3 mouse fibroblasts are labeled with 40 nm gold nanoparticles, and the biological specimen is imaged in a total internal reflection configuration with holographic microscopy. Due to a higher scattering efficiency of the gold nanoparticles versus that of cellular structures, accurate localization of a gold marker is obtained within a 3D mapping of the entire sample's scattered field, with a lateral precision of 5 nm and 100 nm in the x,y and in the z directions respectively, demonstrating the ability of holographic microscopy to locate nanoparticles in living cells environments

Shot Noise in Digital Holography

We discuss on noise in heterodyne holography in an off-axis configuration. We show that, for a weak signal, the noise is dominated by the shot noise on the reference beam. This noise corresponds to an equivalent noise on the signal beam of one photoelectron per pixel, for the whole sequence of images used to build the digital hologram

Video-rate laser Doppler vibrometry by heterodyne holography

We report a demonstration video-rate heterodyne holography in off-axis configuration. Reconstruction and display of 1 Megapixel holograms is achieved at 24 frames per second, with a graphics processing unit. Our claims are validated with real-time screening of steady-state vibration amplitudes in a wide-field, non-contact vibrometry experiment.Comment: Optics Letters (2011) 00

Imaging of a vibrating object by Sideband Digital Holography

We obtain quantitative measurements of the oscillation amplitude of vibrating objects by using sideband digital holography. The frequency sidebands on the light scattered by the object, shifted by n times the vibration frequency, are selectively detected by heterodyne holography, and images of the object are calculated for different orders n. Orders up to n=120 have been observed, allowing the measurement of amplitudes of oscillation that are significantly larger than the optical wavelength. Using the positions of the zeros of intensity for each value of n, we reconstruct the shape of vibration the object.Comment: 6 page