Development of a demountable and see-through hollow cathode (HC) discharge lamp suitable for optogalvanic (OG) spectroscopy is described. The design of the HC lamp is simple, compact, and inexpensive. Lithium, investigated rarely by the OG method, is selected for cathode material as its isotopes are important for nuclear industry. The HC lamp is characterized electrically and optically for discharge oscillations free OG effect. Strong OG signals of lithium as well as neon (as buffer gas) are produced precisely upon copper vapor laser pumped tunable dye laser irradiation. The HC lamp is capable of generating a clean OG resonance spectrum in the available dye laser wavelength scanning range (627.5-676 nm) obtained with 4-(Dicyanomethylene)-2-methyl-6-(4-dimethylaminostyryl)-4H-pyran dye. About 28 resonant OG lines are explicitly observed. Majority of them have been identified using j-l coupling scheme and assigned to the well-known neon transitions. One line that corresponds to wavelength near about 670.80 nm is assigned to lithium and resolved for its fine (S → P) transitions. These OG transitions allow 0.33 cm accuracy and can be used to supplement the OG transition data available from other sources to calibrate the wavelength of a scanning dye laser with precision at atomic levels.

Study of photosynthesis using thermoluminescence (TL) requires precise control of the experimental parameters, particularly the excitation source and the sample temperature. In this paper, we describe the design of an instrument that allows automatic control of various steps of the experiment and present illustrative results to demonstrate its versatility. The temperature sequence, the range and the rate of cooling and heating of the sample can be set and controlled anywhere between −150 and +90 • C. The sample temperature can also be held constant at any temperature in this range to within ±2 • C. Five light emitting diodes, covering discrete wavelengths from 470 to 660 nm and white light, are used for pulsed or continuous excitation. The ultra-high sensitivity and versatility of this instrument enabled two significant observations to be made, being reported for the first time in this paper, namely that (a) TL occurs in photosynthetic and non-photosynthetic materials even without pre-excitation and (b) TL also occurs during the sample cooling phase.

The coherence property of the laser light is an important aspect for the understanding of the optical physics. A modified geometry of the Mach-Zender interferometer has been proposed for measurement of the coherence of the laser. The geometry of the mirrors has been arranged in such a way that the reversible shear interferometer and the Michelson interferometer, both the types of the interferometers are set-up in a single geometry. Using this interferometer, the spatial and the temporal coherence of the laser beam can be measured .The interferometer is simple in design and is useful in the computer assisted visual learning of the coherence at the college and university level education and teaching in optics. Keywords Interferometry,Coherence , Optics SummaryThe coherence property of the laser light is important in understanding of the laser /optics and its various applications in holography etc. The reversible shear interferometer1 provides the measurement of the spatial coherence and the Michelson interferometer measures the temporal coherence of the laser. The conventional young slit method for spatial coherence measurement is not suitable for large diameter laser beams and it also requires multiple measurements. In this paper, a modified geometry of Mach Zender interferometer has been reported which can be used for the spatial coherence in a single measurement as well as for the temporal coherence measurement of the laser beam. The interferometer can be easily used in the large diameter laser beams .The schematic of the interferometer has been shown in the figure-1. Its mirror geometry is similar to the Mach Zender interferometer, the W1 and W2 are two wedges at 450 and mirror M3 is mounted on the translation stage. The incident laser beam is split at wedge W1 and recombine at wegde W2. The one part of the laser beam propagating in the path W1!M1!M2!W2 and the other beam propagating along the path W1!W2!M3!W2, both the beams combine at wedge W2. C is the compensating plate. The wavefront from the earlier path is inverted along a line of folding.