Squeezed states of the electromagnetic field have been generated by nondegenerate four-wave mixing due to Na atoms in an optical cavity. The optical noise in the cavity, comprised of primarily vacuum fluctuations and a small component of spontaneous emission from the pumped Na atoms, is amplified in one quadrature of the optical field and deamplified in the other quadrature. These quadrature components are measured with a balanced homodyne detector. The total noise level in the deamplified quadrature drops below the vacuum noise level.

Observation of squeezed states generated by four-wave mixing in an optical cavity

Nanostructures have attracted huge interest as a rapidly growing class of materials for many applications. Several techniques have been used to characterize the size, crystal structure, elemental composition and a variety of other physical properties of nanoparticles. In several cases, there are physical properties that can be evaluated by more than one technique. Different strengths and limitations of each technique complicate the choice of the most suitable method, while often a combinatorial characterization approach is needed. In addition, given that the significance of nanoparticles in basic research and applications is constantly increasing, it is necessary that researchers from separate fields overcome the challenges in the reproducible and reliable characterization of nanomaterials, after their synthesis and further process (e.g. annealing) stages. The principal objective of this review is to summarize the present knowledge on the use, advances, advantages and weaknesses of a large number of experimental techniques that are available for the characterization of nanoparticles. Different characterization techniques are classified according to the concept/group of the technique used, the information they can provide, or the materials that they are destined for. We describe the main characteristics of the techniques and their operation principles and we give various examples of their use, presenting them in a comparative mode, when possible, in relation to the property studied in each case.

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Characterization techniques for nanoparticles: comparison and complementarity upon studying nanoparticle properties

Particle tracking is of key importance for quantitative analysis of intracellular dynamic processes from time-lapse microscopy image data. Because manually detecting and following large numbers of individual particles is not feasible, automated computational methods have been developed for these tasks by many groups. Aiming to perform an objective comparison of methods, we gathered the community and organized an open competition in which participating teams applied their own methods independently to a commonly defined data set including diverse scenarios. Performance was assessed using commonly defined measures. Although no single method performed best across all scenarios, the results revealed clear differences between the various approaches, leading to notable practical conclusions for users and developers.

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Objective comparison of particle tracking methods

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Methods of Numerical Integration

The theory of image formation is formulated in terms of the coherence function in the object plane, the diffraction distribution function of the image-forming system and a function describing the structure of the object. There results a four-fold integral involving these functions, and the complex conjugate functions of the latter two. This integral is evaluated in terms of the Fourier transforms of the coherence function, the diffraction distribution function and its complex conjugate. In fact, these transforms are respectively the distribution of intensity in an 'effective source', and the complex transmission of the optical system-they are the data initially known and are generally of simple form. A generalized 'transmission factor' is found which reduces to the known results in the simple cases of perfect coherence and complete incoherence. The procedure may be varied in a manner more suited to non-periodic objects. The theory is applied to study inter alia the influence of the method of illumination on the images of simple periodic structures and of an isolated line.

On the diffraction theory of optical images

Image formation in the coherence probe microscope (CPM) and in optical coherence tomography (OCT) are compared. These systems differ in that CPM is a conventional interference microscope, but OCT is a confocal interference microscope. A major disadvantage of CPM for imaging through thick object structures is that there is no optical sectioning for the background image, which can saturate the detector. The behavior of the interference term in the presence of aberrations also exhibits some differences: Aberrations can be compensated in CPM, but not in OCT.

Image formation in low-coherence and confocal interference microscopes

Interferometric profilers suffer from phase ambiguities if the measurement range involves a change in the optical path difference greater than a wavelength This limitation has been overcome by using white light and scanning the object in height We show how an achromatic phase shifter operating on the geometric phase can be used to evaluate the fringe contrast directly and to locate the position of the zero-order white-light fringe along the scanning axis

White-light Phase-stepping Interferometry for Surface Profiling

Characterisation of Fe-oxide nanoparticles coated with humic acid and Suwannee River natural organic matter.

Strictly, to obtain true confocal imaging the detector pinhole must be infinitesimally small, which would of course result in a vanishingly weak image signal. On the other hand, a very large pinhole degrades the confocal imaging effect. So in practice it is necessary to adopt some optimum diameter for the pinhole, which will depend on the design of the microscope, how it is operated, and the type of specimen. The resultant imaging performance then also depends on these various factors. In this way we can compare the performance of different designs of confocal microscope, and also compare them with widefield (WF) microscopes that have electronic image capture coupled with digital three-dimensional (3D) image restoration. In addition, we can understand how best to use the microscope in order to achieve optimum imaging performance.

Signal-to-Noise Ratio in Confocal Microscopes

https://opus.lib.uts.edu.au/bitstream/10453/26659/3/Assessing%20the%20aggregation%20behaviour%20of%20Fe2O3NPs%20-%20Final%20MS%20-%20without%20track%20changes%20v6.pdf

Maitreyee Roy

Papers

Image formation in low-coherence and confocal interference microscopes

White-light Phase-stepping Interferometry for Surface Profiling

Characterisation of Fe-oxide nanoparticles coated with humic acid and Suwannee River natural organic matter.

Signal-to-Noise Ratio in Confocal Microscopes

Assessing the aggregation behaviour of iron oxide nanoparticles under relevant environmental conditions using a multi-method approach