Pulse stretcher with variable pulse length for excimer laser applications.

Area of Science:

• Optics and Photonics
• Laser Physics
• Materials Science

Background:

• Excimer laser systems frequently utilize pulse stretchers to mitigate high pulse peak intensities, crucial for applications like lithography and Raman spectroscopy.
• Material research demands precise control over laser pulse characteristics, including length and intensity, for advanced optical material development.
• Deep-ultraviolet (DUV) optical materials require specialized characterization techniques due to their sensitivity and specific application requirements.

Purpose of the Study:

• To develop and evaluate an imaging-based pulse stretcher for excimer lasers, suitable for pulse length-dependent applications, particularly in material research.
• To assess the compatibility of two 193 nm single-tube excimer lasers (Lambda Physik LPX 240i and Cymer ELS 5600) with the developed pulse stretcher.
• To demonstrate the effectiveness of stretched 193 nm laser pulses in retarding the aging of calcium fluoride (CaF(2)) crystals.

Main Methods:

• Development of an imaging pulse stretcher featuring motorized translation stages for beam splitters, allowing switching between four pulse lengths.
• Characterization of two 193 nm excimer lasers for their suitability with the pulse stretcher, focusing on beam profile and divergence consistency.
• Evaluation of the Lambda Physik LPX 240i excimer laser's combinability with the pulse stretcher using a single cylindrical lens for beam shaping.
• Experimental demonstration of the effect of stretched 193 nm laser pulses on CaF(2) crystal aging.

Main Results:

• The developed pulse stretcher provides identical beam profiles and divergences across different pulse lengths, crucial for consistent material processing.
• The Lambda Physik LPX 240i demonstrated straightforward integration with the pulse stretcher, unlike the Cymer ELS 5600, which exhibited wavefront instability.
• Stretched 193 nm laser pulses were shown to significantly retard the aging process of CaF(2) crystals, indicating potential for enhanced material longevity.

Conclusions:

• The developed imaging pulse stretcher is a versatile tool for pulse length-dependent applications in material research, offering consistent beam characteristics.
• The Lambda Physik LPX 240i is a suitable excimer laser source for integration with this pulse stretcher, facilitating advanced optical material studies.
• The use of stretched 193 nm laser pulses offers a promising method for improving the durability and lifespan of deep-ultraviolet optical materials like CaF(2).