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In this paper, we present an analysis of, to the best of our knowledge, a novel class of the thin multi-trench-assisted optical coupler for multi-sensing of chemical detection. The design structure is an optical waveguide coupler consisting of closely coupled trenches filled with different liquids for chemical sensing. The refractive index profile of the coupler is allowed to vary due to the chemical filled in these trenches. The scalar finite difference method (FDM) is used to analyze the TE (s polarized) as well as TM (p polarized) modes, and thereafter propagate them along the structure through various trenched sections. We excite the structure with the eigenmode profile, which can be well approximated by the Gaussian shape pulse. The trenches with different chemicals and separation between them are well demonstrated in several examples. The main finding of this paper is that the coupling period of the structure can be changed by altering the refractive index of the trench region. In the FDM analysis, we have used the variable discretization step for better accuracy of these results. A new approach based on a thin multi-trench-assisted optical coupler scheme to analyze and design the chemical sensor is then proposed for the first time, to the best of our knowledge, for the detection of adulteration present in, for example, beverages, and in the medical industry.

We report Doppler-free spectroscopy of neutral europium carried out using the saturation absorption technique. In the present experiment, Eu/Ne hollow cathode discharge is used as an atomic vapor source of europium. The Eu transition 4f 7 6s 2 (S8 7/2° )→4f 7 6s6p(P8 9/2 ) at 601.815 nm and 4f 7 5d6s(aD10 13/2° )→4f 7 5d6p(zD8 11/2 ) at 580.027 nm are investigated. The frequency separation between the adjacent hyperfine transitions as well as hyperfine structure (HFS) constants are calculated from the obtained experimental spectra. The HFS constant obtained for the state 4f 7 6s6p(P8 9/2 ) are A 151 =664.8  MHz; B 151 =293.5  MHz, and for state 4f 7 5d6p(zD8 11/2 ), the values are A 151 =7.6  MHz; B 151 =-60  MHz. These obtained values are in good agreement with the results reported in the literature using laser induced atomic beam fluorescence technique.

We present an analysis on the saturation of refractive index modulation of fiber Bragg gratings written in nonhydrogenated Ge-B co-doped single-mode photosensitive optical fiber by partially coherent pulsed UV beams. The UV beams of different spatial coherence properties were generated by second harmonic conversion of high repetition rate, high average power copper vapor laser (CVL) oscillators with different optical resonators. It is observed that for UV beams of higher spatial coherence, the fiber Bragg grating reflectivity growth was faster and saturation of refractive index modulation was higher. The experimental results are explained with the help of a physical model based on exponential decay of defect centers per unit volume on UV absorption in the fiber core. The subsequent increase in the refractive index was attributed to the structural modification and densification of the fiber core.

This paper presents a study on the quality of interference fringes formed from a pulsed UV (255 nm, 5.6 kHz, and 40 ns) source for an application in writing fiber Bragg gratings (FBGs). The interference fringes of separation of about 8 microm, formed by a biprism of apex angle 2 degrees , were studied for their contrast, evolution of contrast, and positional and intensity stability over a period of 5 min (over 10(6) pulses). Second harmonic UV (255 nm) sources of different spatial coherence and pointing stability characteristics were employed as the inputs. It is established that the UV fringes contrast and interference pattern stability with time is largely controlled by the optical resonator geometry of the fundamental wavelength (510 nm) copper vapor laser (CVL) oscillator. In particular, the generalized diffraction filtered resonator (GDFR) CVL produced the highest quality second harmonic beam with the highest fringes contrast and stability. The implications of these results were studied by employing these UV sources for the fabrication of the C-band FBGs by a 24 degrees apex angle biprism.

The conversion efficiency in second-harmonic generation of an amplified beam in a master-oscillator power amplifier copper-vapor laser (CVL) is lower than that of the oscillator beam alone. This lower efficiency is often vaguely attributed to wave-front degradation in the amplifier. We investigate the role of wave-front degradation and thermal dephasing in the second-harmonic generation of a CVL from a beta-barium borate crystal. Choosing two beams with constant intrapulse divergence, one from a generalized diffraction filtered resonator master oscillator alone and other obtained by amplifying oscillator by use of a power amplifier, we show that at low flux levels the decrease in efficiency is due to wave-front degradation. At a fundamental power above the critical power for thermal dephasing, the decrease is due to increased UV absorption and consequent thermal dephasing. Thermal dephasing is higher for the beam with the lower coherence width.

We present results of comparative time-resolved coherence studies on a single pulse from amaster oscillator power amplifier (MOPA) copper vapor laser with generalized diffraction-filtered and unstable resonators as master oscillators. It is shown that, unlike the conventionally used unstable-resonator MOPA reported in literature, the coherence of a generalized diffraction-filtered resonator MOPA pulse is fairly independent of the delay between the oscillator and the amplifier. It also remains constant throughout the pulse, with the result that the flux is constant over a large range of the delay.

The results of a study on the spatial coherence of a generalized diffraction-filtered resonator (GDFR) copper vapor laser (CVL) for various magnifications are presented. The coherence width and output power are compared with that of unstable resonators (UR's) of equivalent magnifications. It is established, by use of reversal shear interferometry, that the GDFR CVL beam has better spatial coherence and average power characteristics than the UR CVL beam for equivalent resonator magnifications.

A simple experimental procedure is described for the precise measurement of focal lengths of medium-sized convex mirrors. This procedure is a modification of the conventional method reported in the literature. It has enabled us to minimize the errors introduced because of bench corrections and depth of focus of optical components that are generally encountered with conventional methods. The accuracy of the procedure has been found to be ±0.3%. The results of the measurements on a few test convex mirrors and experimental parameters are reported.

Photoacoustic spectroscopy, using a PZT transducer, is a quick, direct, and accurate technique to measure ink colors from the absorption region and maximum absorption position.