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Quantum key distribution (QKD) has raised increased attention over the past years as one of the most attractive quantum technologies for practical implementation. QKD has already been implemented in intra-city networks all around the world. But up to now, bridging global distances with quantum communication remains an outstanding challenge. A promising candidate to provide this link is via optical...
Quantum interference forces two indistinguishable input photons to depart a beamsplitter in the same (of two possible) spatial output modes; this is known as the Hong-Ou-Mandel (HOM) effect. It provides a quantitative way of measuring the distinguishability between two photons and also has been utilised to determine their relative temporal delays [1, 2]. HOM interferometry offers numerous advantages...
Fluorescence microscopy is a widely used tool in cell biology to resolve subcellular structures and reveal dynamic processes, such as molecular transport in or between cells. In the last decade, several techniques were developed that have enabled us to overcome the optical diffraction limit and to resolve even finer spatial structures.
Continuous monitoring or tracking of a quantum system is essential to high-sensitivity measurement of time-varying quantities. We estimate spin precession of a magnetically-sensitive atomic ensemble by measuring spin projectors Fα at different times. Such projectors do not commute, and thus quantum measurement back-action (QMBA) necessarily enters the spin measurement record, introducing errors and...
Quantum-optical states, such as single-photons or quadrature-squeezed light, used for processing quantum-information easily reach optical bandwidths, however homodyne-detection — a major quantum-information tool, is sub-GHz limited. Using optical parametric-amplification we demonstrate effectively bandwidth unlimited optical-homodyne measurement.
When coherent light propagates through a disordered system, such as white paint or biological tissue, its spatial properties are mixed and the resulting transmitted field forms a speckle pattern. Although the size of a speckle grain is diffraction-limited, this complex interference figure is detrimental for all conventional imaging systems. Over the last decade, wavefront shaping techniques have opened...
Optical imaging through complex media such as biological tissue or white paint remains a daily challenge as spatial information gets mixed because of multiple scattering. Without any ballistic light, common microscopy techniques become useless. Over the last decade, spatial light modulators (SLM) have become the indispensable tool to overcome scattering thanks to their millions of degrees of freedom...
In the process of the lens production it is extremely important that a total time of measuring the lens thickness, taking into account also the time needed to insert the lens into a system, should be short enough to test the substantial part of the series of products. Currently used methods of measuring lens thickness apply various solutions [1, 2], but none of them offers a fast and cost effective...
Femtosecond mode-locked fiber lasers have been actively employed in many practical applications such as micro-machining, corneal surgery and multi-photon imaging, thanks to their compactness, alignment-free operation, and low cost. To enhance the long-term stability and self-starting operation of mode-locked lasers, saturable absorber (SA) devices, such as semiconductor saturable absorber mirrors...
Infrared spectroscopic measurements are a key tool for species identification and substance detection. Growing importance falls to the mid-infrared 3–12 μm range, where strong, fundamental spectroscopic features are found. One issue especially in stand-off remote sensing scenarios with low-intensity backscattered signals is the limited sensitivity of available detectors for the (MIR) wavelength range...
The use of stimulated Raman scattering (SRS) for Kerr comb generation is very attractive because it allows us to generate long-wavelength light, particularly in the mid-infrared wavelength regime, where the wavelengths are useful for sensing applications. Recently, the generation of comb light and the interaction between transverse modes with the SRS process using a crystalline microcavity have been...
Measurements of quantum states of photons are conventionally performed with series of optical elements in bulk setups [1] or optical chips incorporating multiple tunable beam splitters. Here, we suggest and develop experimentally, for the first time to our knowledge, a new concept of quantum-polarization measurements with a single all-dielectric resonant metasurface [2]. The operating principle is...
The spatial structure of a photon has proved to be indispensable resource allowing the experimental realization of free-space quantum cryptography or high dimensional entanglement. Although efficient methods for manipulating spatial characteristic of individual photons can be easily transferred from the field of classical optics, their spatial structure cannot be measured using the standard interferometric...
We demonstrate an optomechanical system with quantum cooperativity Cq = 4g2/κγ >> 1 already at moderate cryogenic temperature [1]. It is realised as a membrane-in-the-middle system [2] with a high-stress silicon nitride membrane. Here, y = kBT/ħQ is the quantum decoherence rate of the mechanical system due to its thermal bath at temperature T∼4 K, and Q∼107 the mechanical quality factor. In...
When a photosensitive (PS) fiber is exposed to UV-irradiation, a permanent refractive index change is induced in the core. As a result, according to Kramers-Kronig relations, the absorption coefficient (α) is also increased. This increment of the absorption can lead to a significant heating of the fiber when it is illuminated by a moderate optical power. Thermal effects may produce spectral changes...
Steam Quality (dryness fraction) is defined by the presence of water droplets in steam. It is undesirable as lower steam quality leads to poor heat transfer characteristics, erosion of piping and critical equipment such as turbine blades [1]. Sample based measurement, such as separating calorimeter [2], throttling calorimeter and online measurements (optical based [3]) are different methods for dryness...
Spatially entangled photon states are used in experiments addressing fundamental properties of quantum mechanics as well as practical applications [1]. Thereby, the use of these states demands for time-saving detection mechanisms, capable of measuring coincidences between spatially separated photons with high spatial and temporal resolution. In this work, we demonstrate coincidence detection of spatially...
In the last decade, ultrashort pulsed lasers have been developing to a precise tool for material processing. Experimental and theoretical studies on the laser ablation efficiency of metals have demonstrated a high degree of dependency on the laser pulse duration. Within these studies, the transient energy deposition in the material defines the thermal and mechanical material response after laser irradiation.
Metal laser additive manufacturing (LAM) provides unique possibilities for the fabrication of complex parts in many key industrial areas such as aerospace, automotive, and healthcare. However, due to variations in part geometry, local environment, and the inherent stochasticity of the laser melting process, reproducibility in final part morphology and characteristics is a major concern. In this paper,...
Conventional sampled grating distributed-Bragg-gratings (C-SGDBRs) are widely used in tunable DBR lasers [1], and more recently have been used to precisely control the wavelength spacing in arrays of DBR lasers for use in WDM systems [2], and as the reflectors in THz repetition frequency (Fr) semiconductor mode locked lasers (SMLLs) [3]. However, the effective coupling coefficient, κ, of a C-SGDBR...
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