A. Ramalingam

Gain studies of Rhodamine 6G dye doped polymer laser

Solid state dye doped polymer is an attractive alternative to the conventional liquid dye solution. In this paper, the laser characteristics of Rhodamine 6G (Rh6G) doped polymethyl methacrylate (PMMA) rods, modified with ethyl alcohol (EtOH), are examined by nitrogen laser, and second harmonic Nd : YAG laser excitations in a transverse pumping configuration and the variation of small signal gain of the dye in solid medium for different pump powers are studied. The photobleaching of dye doped polymer rod is also studied.

Dual amplified spontaneous emission from 7-amino-4-methyl coumarin dye

Abstract This paper reports on the dual amplified spontaneous emission observed from solutions of 7-amino-4-methyl coumarin dye (coumarin 440) in certain solvents such as n -butyl acetate, dioxane etc. when exposed to high power nitrogen laser excitation. The results suggest that twisted intramolecular charge transfer coumarin photoisomers which form exciplexes with the solvent molecules have enough gain to produce amplified spontaneous emission even where there is apparently no detectable fluorescence.

Role of dipole moment of solvents in formation and stabilization of the TICT states in Coumarin 445 under nitrogen laser excitation

In this paper we report the observation of dual Amplified Spontaneous Emission (ASE) from solutions of 7-ethylamino-4-methyl coumarin dye (Coumarin 445) in certain solvents such as n-butyl acetate, dioxane etc. when pumped by high power nitrogen laser. The two ASE bands appear to be from two different excited species (ICT and TICT conformation) one of which is the precursor of the other. The spectral characteristics of dye Coumarin 445 depend upon the solvent environment. The TICT coumarin photoisomers, which form exciplexes with the solvent molecules, have enough gain to produce amplified spontaneous emission even when there is apparently no detectable fluorescence. The behaviour of this dye in the excited state is studied by measuring the small signal gain and variation of the gain slope with temperature in different solvents. It is observed that polarity of the solvent plays a more dominant role in formation and stabilization of TICT states.

Photophysics of TICT states of 7-diethylamino-4-methyl coumarin dye by energy transfer techniques

Coumarin 1 exhibited dual amplified spontaneous emission (ASE) in certain solvents under nitrogen laser excitation. These emissions are known as normal and anomalous emissions. The anomalous emission corresponds to TICT state and it does not have a corresponding fluorescence peak. Energy transfer techniques have been used to study the photophysics of TICT states and the characteristics of dual ASE bands of the dye coumarin 1.

Energy transfer rates in a 7-diethylamino-4-methylcoumarin-rhodamine 6G binary dye mixture laser

Abstract In this paper an attempt is made to calculate the radiative and non-radiative Forster-type energy transfer rates in a binary dye mixture laser. The dyes used were 7-diethylamino-4-methylcoumarin (DAMC) and rhodamine 6G (R6G) and the solvent employed was 2-methoxyethanol. The Forster transfer rate was found to be almost five times as large as the radiative transfer rate in this DAMC-R6G dye laser system.

An instrument for online measurement of structural orientation in translucent polymer sheets

In many applications of polymer materials, a high tensile strength is required. There is a definite correlation between the degree of orientation of molecular chains achieved in the orientation process and the tensile strength obtained. In this work, we describe design and fabrication details of a device, ‘Laser based polymer orientation grader’, for online measurement of the degree of orientation to obtain a high consistent tensile strength as output. This instrument has been designed making skilful use of the optical anisotropic property of the oriented polymer strip. The principle is based on the fact that the spatial distribution of laser light passing through the translucent polymer sheet depends on the degree of orientation of long chain molecules in the sheet. The method has potential online application in monitoring and controlling of anisotropy in manufacturing processes.

Energy transfer in coumarin 503 dye doped polymer laser

Solid state dye doped polymer is an attractive alternative to the conventional liquid dye solution. In this paper, the laser characteristics of Coumarin 1(C1), Coumarin 503 and a mixture of C1 and C503 doped polymethyl methacrylate rods modified with ethyl alcohol are studied under nitrogen laser excitation in a transverse pumping configuration and the variation of gain of the dye in solid medium for different pumping powers are studied. The photo bleaching of dye doped polymer rod is also studied.

Surface hardening of oil-hardened nonshrinking steel using ruby laser

Surface modification of metals and alloys using lasers has acquired considerable importance because the changes achieved are highly localized and superficial. In this process the mechanical and structural properties of the bulk are retained as such because of the high temperature gradient and high rate of change of temperature that are unattainable by conventional methods. The present report is on surface hardening of oil-hardened nonshrinking (OHNS) steel using Ruby laser in normal mode. It is found that surface hardening increases thrice the size of base material and the microstructure of the laser-heated zone changes from pearlite phase to martensite phase.

Effect of solvents on the photophysical properties of substituted imidazonaphthyridine derivatives.

The absorption and fluorescence characteristics of three substituted imidazonaphthyridine derivatives are studied in a series of organic solvents. The variation of Stokes shift with the polarity parameter of the solvent is studied and the excited state dipole moment of these derivatives is higher than the ground state dipole moment. The fluorescence lifetime profile shows single exponential decay in all the solvents. The fluorescence quantum yield, radiative and non-radiative rate constants are also calculated and these parameters show much variation in the change in substitution of these derivatives.

Calibration of angular motion of a scanning mirror mechanism using a lateral-effect position-sensitive photodetector

This paper describes a noncontact and computer compatible test setup to calibrate the angular motion of a life test model of a scanning mirror mechanism using a lateral-effect position sensitive photodetector (LPSD). Laser based measurements of its movements using the LPSD adds up the suitability of this mechanism to very high resolution radiometer effectively. The description of the scan mirror mechanism and the existing calibration test methods are briefed. The characteristic properties of the LPSD are discussed. Experimental details and the results obtained are presented.