Abstract

Abstract
We model the photocurrent of a depth-scan (A-scan) from an optical coherence tomography (OCT) system, using a linearly polarized thermal source, as an electronically filtered doubly-stochastic Poisson process, and we obtain its time-varying second-order statistics. We derive an expression for the instantaneous signal-to-noise ratio (SNR) of time-domain OCT which is more general than the previously reported time-averaged expressions. Unlike previous work, our analysis combines shot noise, due to detection of coherent light, and photon excess noise, due to fluctuations in the optical field, into a single noise source that we refer to as the photoelectron noise. Similar to previous results, our SNR is dominated by a term similar to shot-noise when the reference optical power is low and by a term similar to photon excess noise when the reference power is high. © 2005 SPIE and OSA.

Abstract
In optical coherence tomography (OCT). it is often assumed that the signal-to-noise ratio is limited by shot noise. However, a high data acquisition rate and a low target reflectivity require operation under high optical power. Balance detection is used with the aim to bring the noise close to shot noise regime, but this is not all the time achievable in practice. If the balance detection is ideal, the limiting factor is the beat noise. This is proportional to the stray reflectance in the object arm and inverse proportional to the effective noise bandwidth. It was often noticed that the limiting theoretical value for the S/N ratio for a given stray reflectance and optical source bandwidth could not be experimentally achieved. In the present study, we develop a new model where we address this issue by taking into account the limited spectral response of fiber based balanced detection receivers. We show that due to mismatches in the balanced receiver, excess photon noise has a larger contribution than normally expected. with important implications in the maximum achievable SNR. The theoretical model developed leads to a redefinition of the effective noise bandwidth to take into account the non-flat response of the directional coupler used in the balanced stage. The model is capable to explain the limitation of SNR observed in practice when stray reflectances within the interferometer are brought to infinitesimal values. The model guides optimization of parameters in order to maximize system performance. for a given optical source power and directional coupler characteristics. In this paper we present experimental results to validate the theoretical model. Such S/N analysis is paramount in the modem OCT technology. which makes use of wide bandwidth sources in the quest for high-depth resolution.

Abstract
Two and three SLD diodes are grouped together in order to obtain a compounded source of wide band for OCT investigations. One SLD has a two-lobe spectrum around 840 nm and a compounded spectrum is achieved by using SLDs of smaller wavelengths. This has two advantages: (1) the smaller the wavelength the lower the loss of power through the vitreous due to water absorption; (2) medium band, standard SLDs if used bring a more significant reduction to the coherence length than their counterparts, of medium band but centered at longer wavelength. We show that it is possible to obtain high resolution OCT images with an inexpensive, compact, and easy to operate source.

Abstract
The bottom electrode crystallization method was used for the heat-treatment of amorphous Pb(Zr-0(52)., Ti-0.48)O-3 thin films deposited by radio-frequency magnetron sputtering on Pt/Ti/SiO2/Si substrates. Two different heating and cooling rates were applied and two different contact wires (W and Pt) were alternately used for the Joule heat generation in the Pt bottom electrode. The dielectric and ferroelectric properties of the films were compared with the properties of the films crystallized using halogen lamp annealing in the same conditions. All the PZT samples showed similar ferroelectric properties at room temperature, with high dielectric constant and remanent polarization values as well as good resistance to ferroelectric fatigue, the Al/PZT/Pt/Ti/SiO2/Si capacitors having low leakage currents. The experimental results obtained show that the bottom electrode crystallization method is a cheap and low power consumption method which can successfully replace the classical crystallization methods.

Abstract
We derive the effects of time refraction in a dispersive medium. A new type of radiation process is described that extends the concept of Unruh radiation to a non-accelerated but superluminal perturbation of the optical properties of a medium. The case of a plasma is considered as an example.