Study on the Wavelength-Dependent Temporal Waveform Characteristics of a High-Pressure CO₂ Master Oscillator Power Amplifier System

This study systematically investigates the temporal characteristics of a high-pressure CO₂ master oscillator power amplifier (MOPA) system under tunable spectral lines. Based on a continuously tunable CO₂ oscillator–amplifier system, we experimentally measured the variation in the laser pulse width before and after amplification at different spectral lines, with the oscillator and amplifier operating at pressures of 7 atm and 3 atm, respectively. The results indicate that, for most spectral lines, the laser pulse width remained nearly unchanged after amplification. However, at certain spectral lines, a distinct phenomenon was observed: pulse broadening for strong lines and pulse narrowing for weak lines. To explain this phenomenon, theoretical calculations were conducted based on a high-pressure CO₂ six-temperature model, and the experimental results were analyzed from the perspective of small-signal gain dynamics. This study reveals that variations in the laser pulse width primarily originated from differences in the gain build-up time across different spectral lines, which in turn influenced the amplification of both the pulse pedestal and the main pulse. For strong spectral lines, the amplifier gain built up rapidly, leading to more uniform amplification of the entire laser pulse and resulting in pulse broadening. Conversely, for weak spectral lines, the amplifier gain built up more slowly, with amplification primarily concentrated in the main pulse, causing a reduction in the pulse width. This finding has significant implications for optimizing narrow-pulse CO₂ lasers and provides crucial insights into the temporal characteristics of applications, such as laser isotope separation and extreme ultraviolet (EUV) light source generation.