Characteristics and Absorption Coefficient of Co2 Laser in Natural Gas Mixtures

This work was arranged to develop scientific and engineering database on the study of cw / repetitively pulsed CO2 laser in terms of its characteristics and absorption coefficient in natural gas mixtures. The laser system is operated both in continuous wave mode as well as in pulse mode at 10.6µm wavelength range of infrared electromagnetic spectrum. The study on CO2 laser system consists of two parts. In the first part, the measurements on the characteristics of cw / repetitively pulsed CO2 laser system are done at 10.6 µm wavelength. The output parameters of CO2 laser are carried out in detail to determine the laser characteristics for getting maximum output energy and power subject to various variable such as pulse repetition rate, discharge current, duty cycle and pulse duration. Different aspects of CO2 laser are studied to determine the laser characteristics between various design parameters and the effect of varying one parameter on others. The frequency and current limits regarding maximum and minimum output energy and power are presented. The maximum pulse energy is achieved at 32mJ when the laser operated at 10mA discharge current with 50 Hz pulse repetition rate. A maximum power of about 11 watts is measured at a current of 10mA. The output energy and power is found to decrease with further increase in pulse repetition rate and discharge current. This is due to the saturation of the gas molecules inside the laser tube. In the second part of the project, the experimental work on the absorption coefficient of CO2 laser in compressed natural gas mixtures are measured at variable laser energy and pressures operated at 295K temperature. The measurements are done using optical transmission loss technique with 19% transmission loss due to the absorption by the optical system. The absorption data showed a strong dependence on both laser energy and pressure. It was found that natural gas mixtures absorb laser light the most, followed by pure natural gas and the lowest laser absorption coefficient is air. The results are found to follow the exponential law of absorption that is called as Beer-Lambert Law. The purpose of this study is to explore the application of CO2 laser especially in the area of combustion of natural gas. For the first step, the characteristics in terms of laser energy and power and its absorption in natural gas need to be studied.

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