1,721,302 research outputs found
Single-pixel imaging pattern sets and their implications on scene reconstruction
Full text linkAlternatives to focal-plane detector arrays have emerged in recent years and are now being widely investigated. One of the most promising of these are single-pixel imaging techniques. Single-pixel techniques recreate a scene using the knowledge of projected patterns and the measured backscattered signals. This research investigates the implications of using idealised patterns, Fourier-transformed patterns and camera-captured patterns generated by plane wave decomposition methods. Hadamard patterns are projected into the far-field of the phased-array modulator source and used for robust reconstruction in a reflective arrangement. The choice of the optimal pattern sets from these sources are used for single-pixel imaging reconstruction and compressed sensing. The technique is robust to poor signal-to-noise conditions and is applicable in cases where a limited number of measurements are possible. Our technique and methodology can be further applied to any region of the electromagnetic spectrum where phased-array sources are available, such as in the radar regime
Bell inequality in chiral liquids
Full text linkOptical activity is a macroscopic property of chiral molecules which manifests as a rotation of the plane of linear polarization when light passes through a sample. We have developed a compact Bell inequality experiment for quantum probing of chiral liquids, based on polarization measurements. In particular, we show that we can use a Bell-type inequality configuration to measure the optical activity of D-Limonene, a chiral molecule which is a major component in the oil of citrus fruit peels
Photon bunching in a rotating reference frame
No full textAlthough quantum physics is well understood in inertial reference frames (flat spacetime), a current challenge is the search for experimental evidence of nontrivial or unexpected behavior of quantum systems in noninertial frames. Here, we present a novel test of quantum mechanics in a noninertial reference frame: we consider Hong-Ou-Mandel (HOM) interference on a rotating platform and study the effect of uniform rotation on the distinguishability of the photons. Both theory and experiments show that the rotational motion induces a relative delay in the photon arrival times at the exit beam splitter and that this delay is observed as a shift in the position of the HOM dip. This experiment can be extended to a full general relativistic test of quantum physics using satellites in Earth’s orbit and indicates a new route toward the use of photonic technologies for investigating quantum mechanics at the interface with relativity
Topology of optical vortex lines formed by the interference of three, four, and five plane waves
No full textWhen three or more plane waves overlap in space, complete destructive interference occurs on nodal lines, also called phase singularities or optical vortices. For super positions of three plane waves, the vortices are straight, parallel lines. For four plane waves the vortices form an array of closed or open loops. For five or more plane waves the loops are irregular. We illustrate these patterns numerically and experimentally and explain the three-, four- and five-wave topologies with a phasor argument
Laser beams: knotted threads of darkness
No full textDestructive interference may lead to complete cancellation when light waves travelling in different directions cross, and in three-dimensional space this occurs along lines that are vortices of electromagnetic energy flow. Here we confirm theoretical predictions by experimentally creating combinations of optical laser beams in which these dark threads form stable loops that are linked and knotted
Multipoint viscosity measurements in microfluidic channels using optical tweezers
No full textWe demonstrate the technique of multipoint viscosity measurements incorporating the accurate calibration of micron sized particles. We describe the use of a high-speed camera to measure the residual motion of particles trapped in holographic optical tweezers, enabling us to calculate the fluid viscosity at multiple points across the field-of-view of the microscope within a microfluidic system
Static Fourier transform spectrometers and laser wavelength meters
Full text linkThis thesis reports the development of novel static Fourier transform spectrometers based upon Wallaston prisms and compact detector arrays. The path difference between orthogonal polarisation states of the input light varies smoothly across the aperture of the prism forming an interferogram in the spatial, rather than temporal, domain that is recorded with the detector array. A Fourier trans¬ form of this interferogram gives the spectral distribution of the incident light. The elimination of moving parts from the design makes the recorded interferogram inherently stable.
I have developed an improved spectrometer utilising Wallaston prisms fabricated from materials of opposite sign birefringence. This new instrument has a significantly increased field of view compared with previous Wollaston prism based spectrometers.
Additionally my work has involved the construction and evaluation of spectrometers for operation in the ultraviolet, visible and infrared regions of the spectrum. These spectrometers have been applied to the analysis of gasolines. Important properties such as gasoline brand and octane number have been identified from ultraviolet and near-infrared spectra using principal component analysis. Finally, I adapted the spectrometer design to make a fibre-coupled laser wavelength meter based on a modified Wollaston prism. For a narrow linewidth source a fringe period measurement technique, used as an alternative to the Fourier transform algorithm, obtains precision measurement (1 part in 10^6) of the centre wavelength. The wavelength meter and spectrometers have numerous applications in the held of general laboratory instrumentation and their robust, compact nature makes them particularly suitable where held based operation is required
Implementing optical tweezers at high pressure in a diamond anvil cell
No full textDiamond anvil cells allow us to study the behaviour of materials at pressures up to hundreds of gigaPascals in a small and convenient instrument, however physical access to the sample is impossible once it is pressurised. Optical tweezers use tightly focussed lasers to trap and hold microscopic objects, and their ability to measure nanometric displacements and femtonewton forces makes them ubiquitous across the nano and bio sciences. We show that optical tweezers can be used to hold and manipulate particles in such a cell, in the ``macro tweezers'' geometry allowing us to use objective lenses with a higher working distance. Traps are structured to overcome the limitations imposed by the sample cell. Wedemonstrate the effectiveness of the technique by measuring water's viscosity up to 1.2 GPa. The maximum pressure reached was limited by the water crystallising under pressure
Optical spanners and improved optical tweezers
Full text linkThis thesis describes the experimental and theoretical work that investigated the transfer of orbital angular momentum from light to matter. This was achieved by combining two established areas of laser physics which were "optical tweezers" and Laguerre-Gaussian laser modes. The optical tweezers are essentially a tightly focussed laser beam from a high numerical aperture microscope objective lens, which traps particles in three dimensions just below the beam focus. By incorporating a Laguerre- Gaussian laser mode into the tweezers system, the trapping efficiency was doubled. These improved optical tweezers have been successfully demonstrated both theoretically and experimentally. In addition to the spin angular momentum which is associated with the polarisation state, the Laguerre-Gaussian laser modes also possess orbital angular momentum. The "optical spanners" utilised this property by transferring orbital angular momentum from the laser beam to the trapped particle, causing it to rotate whilst being held in the optical trap. This effect was theoretically modelled and experimentally observed. Using the optical spanners, the spin angular momentum of the laser was used to directly cancel the orbital angular momentum in the beam, which was observed as a cessation in rotation of the trapped particle. This demonstrated the mechanical equivalence of the spin and orbital components of angular momentum in a light beam, and gave experimental evidence for the well defined nature of the orbital angular momentum present in Laguerre-Gaussian laser modes
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