CO2 Laser Design, Construction and Evaluation of Its Effect on Semiconductors Electrical Properties

Abstract

A homemade CO2 laser system have been designed, and constructed in the frame of this work, in addition to that, a locally made power supply was used. The performance of the constructed high voltage DC power supply from 0 - 30 KV and discharge current of 100 mA with high efficiency of electrical output power was achieved. The laser output power was achieved at 22 mbar pressure of gases mixture composed of: 10% CO2, 10%N2, 80%He with 15 mA current at high voltage of 4.14 KV with an efficient cooling temperature of 15 Co. The produced laser power was 13 watt. The system efficiency was measured from the input electrical power and electrical energy generated inside a laser cavity, which approximately equal 20%. Efficient cooling system was utilized to maintain proper cooling for the discharge tube. The output spectra of the discharge intensity have been investigated through constructed thermistor and semiconductor diode connected to the computer via CASSEY Lab. amplifier. In particular, the data were collected and analyzed using Cassey Lab and ORIGN program. In the approach of manufacturing infrared filter suitable for filtering CO2 laser output, a new method for selection of CO2 wavelengths in infrared region has been utilized using different chemical compounds. The spectra of three chemical compounds, ZnS, CaF2, and KBr, present in different concentrations and different ratios were measured in the region from 2.5 – 25 µm using IRFT spectrometer. The spectra show high transmission percentage for two mixtures, (CaF2 and KBr) for wavelength 9.4 μm and (ZnS, CaF2 and KBr) for 10.6 μm only. Then filters were manufactured from these compounds in different thickness and different concentrations in order to be used with the CO2 laser beam in any desirable wavelength form the two mentioned above, plus with the control of the filter thickness, the transmission percentage can be controlled. Investigation of CO2 laser effect on semiconductor Si and Ge properties, such as I-V characteristics, resistance under temperature dependency, were outlined in this thesis. In the present study the characteristic variations due to the improvement in material structure is particularly evidence of recrystallization process occurred in the semiconductor caused by a laser power during the annealing process.