Diamond photodetector response to deep UV excimer laser excitation

Diamond photoconductive detectors have previously been shown to be suitable for detection of deep ultraviolet nanosecond-scale pulses from excimer lasers, which are to be used in next generation lithographic systems. Using simple test circuitry and low bias voltages easily measurable responses were observed when these detectors were illuminated with laser pulses at typical laser fluence levels. However, as the laser fluence is increased the detector response appears to broaden and change shape as well as increase in magnitude. In this paper we present analysis of the response of these detectors. This analysis shows that over the laser fluence range used the magnitude of the detector response exhibited a linear response. By approximating the temporal evolution of the laser pulse and simulating the transfer characteristics of the test circuit it can be seen that the pulse broadening and shape change seen with increasing fluence can be explained by the test circuit. The shape of the detector response, therefore, closely resembles the temporal shape of the laser pulse, demonstrating that these devices are fast enough to give a true representation of 10–15 ns laser pulses at a wavelength of 193 nm.