Second harmonic conversion of 10 µm emissions of pulsed and CW CO₂lasers in ZnGeP₂

Abstract

The paper reports on the satisfactory performance of a ZnGeP 2 crystal towards second harmonic conversion of a pump beam at 10 μm wavelength and thus establishes its utility in the generation of coherent radiation not only around 4.5 μm but also in the neighbourhood of the 5 μm region of mid-infrared. Experimental results comparing performance of a thin crystal when pumped alternately with the emissions of continuous wave (CW) and TEA CO 2 lasers are presented. The performance was also studied as a function of the duration of the pump TEA CO 2 laser pulse and the observed anomaly is qualitatively explained. The significant increase in conversion efficiency in the case of pulsed operation is attributed to the much higher irradiating intensity to which the crystal is subjected to in comparison with the CW case. Of particular interest is the finding that the pump intensity below which the second harmonic generation process ceases is lower by almost 3 orders of magnitude in case of the CW operation.