Om Prakash

Cylindrical-lens-based wavefront-reversing shear interferometer for the spatial coherence measurement of UV radiations

We present the design and results of a cylindrical-lens-based reversal shear interferometer for measuring the spatial coherence of partially or fully coherent UV beams. This is a modified Michelson interferometer consisting of only four optical components. The wavefront is reversed in one of the interferometers arm by the combination of a plane mirror located at the focal plane of a cylindrical lens. The selected wavefront can be sheared at any arbitrary angle with respect to the incident wavefront by rotating the cylindrical lens, thus enhancing the capability of this design for a real 3-D wavefront evaluation. This interferometer is used to measure the spatial coherence of 255-nm UV radiations obtained from the second harmonic of a copper vapor laser for pump beams of different spatial coherence characteristics, a result being reported for the first time.

Comparative study on second harmonic conversion and saturation characteristics of three copper vapor laser beams of same average power and different spatial coherence

This paper presents a comparative study on second harmonic conversion and saturation behavior of three copper vapor laser (CVL) beams of same average power up to 11 W (510 nm), however with different spatial coherence width of 17%, 35%, and 100% of the full beam cross-section. The nonlinear crystal employed is beta barium borate. It is observed that the trends in second harmonic (SH) conversion efficiency and its saturation are widely different for the three CVL pump beams. As expected, the conversion efficiency scaled up with increase in pump power. However, very interesting trends are observed in SH saturation characteristics with scaling of pump beams spatial coherence. For lower coherence CVL beam, the saturation of SH efficiency is observed at lower pump flux and at higher average power. Also, the saturation occurred at lower SH efficiency for CVL beam of lower spatial coherence. The fall in the SH efficiency after the peak is more rapid for lower spatial coherence pump beam. The experimental trends are explained in terms of combined effect degree of spatial coherence of pump beams and the thermal dephasing in the nonlinear crystal by high pump average power.

Influence of endosperm texture on milling, chemical composition and nutritive quality in maize.

Three maize varieties namely Vijay, SO/SN composite and Shakti, which differ in their nutritional quality and endosperm texture were processed to prepare semolina (sooji) and process-flour. The nutritional quality of these products was determined and compared with whole kernel flour of the respective variety. Distinct differences in milling and chemical composition of three varieties were recorded. In quality evaluation tests lysine and tryptophan content, biological value and true digestibility were better in semolina and process-flour. Moreover, decrease in acid value in semolina and process-flour compared with whole maize flour recorded in all the varieties suggested improvement in shelf-life.

Studies on Spatial, Spectral, and Energy Characteristics of Copper-HBr Laser Radiations

This paper presents, for the first time, a study on the pulse-to-pulse variation in the spatial, spectral, and energy characteristics (pointing instability, divergence, intensity, as well as the emission line-width and their fluctuations) of both green and yellow radiations of a copper-HBr laser (Cu-HBrL). The experimental study was performed in a high power (specific power: 70 W/L, total power: 72 W), 18 kHz repetition rate Cu-HBrL for different wall plug electrical input powers (6-9.5 kW) and HBr concentrations (5%-9%). These observations are supplemented with studies on near field spatial intensity and temporal profiles under all working conditions. It is observed that the characteristics are widely different for the two radiation components. The experimental observations are supported by comprehensive analysis in terms of input power coupling, laser gain and its radial distribution, thermally induced wave-front aberrations, optical noise contribution, and laser kinetics.

Effect of buffer gas pressure on the spatiotemporal evolution of small-signal gain in copper vapor laser

We report the effect of buffer gas neon pressure on the spatiotemporal small signal gain evolution characteristics of a copper vapor laser CVL. The CVL discharge tube of diameter 47 mm and length 150 cm is studied for neon pressure from 20 to 70 mbar. The gain evolution is mapped by a specially generated 6-ns, 510.6-nm probe pulse. The evolution of gain at the center and at the edge are found to be widely different for different gas pressures. At lower pressure 20 mbar, the gain at the edge is higher compared to that at the center, however, the situation is reversed at higher pressure 70 mbar. The increased laser-circuit impedance matching and the reduced discharge plasma skin effect with increase in buffer gas pressure are the possible mecha- nisms responsible for such a changeover.

Surface Modified Long Period Fiber Grating Sensor for Rapid Detection of Aspergillus Niger Fungal Spores

ABSTRACT We present development of a compact and label-free sensor based on the surface modification of copper vapor laser fabricated long period fiber gratings for detection of airborne Aspergillus niger (A. niger) fungal spores. Surface of sensors were functionalized with monoclonal glucose oxidases IgG1 for target-specific covalent binding. In process of functionalization and binding of 103 cfu/ml of pathogenic A. niger fungal spores, notable shorter wave transition in resonance wavelength from 1562.93 nm to 1555.97 nm, and significant reduction in peak loss from 61.72 dB to 57.48 dB were recorded. The implementation was cost effective and yielded instantaneous results.

A simple design of a reflectometer

A simple design for a double-beam reflectometer to measure absolute values of reflectance and transmittance of specularly reflecting surfaces at normal incidence without requiring any reference standard is discussed.