Extreme ultraviolet light from a tin plasma driven by a 2-µm-wavelength laser

Area of Science:

• Plasma Physics
• Laser-Induced Breakdown Spectroscopy
• Materials Science

Background:

• Laser-produced plasmas are essential for generating extreme ultraviolet (EUV) radiation.
• Optimizing laser parameters is critical for enhancing the efficiency of EUV generation.

Purpose of the Study:

• To experimentally investigate and compare the generation of EUV radiation from laser-produced plasmas using 1-µm and 2-µm laser wavelengths.
• To determine the impact of laser wavelength and intensity on conversion efficiency (CE) for EUV generation at 13.5 nm.

Main Methods:

• Irradiation of a planar tin target using 4.8-ns laser pulses from a KTP-based 2-µm master oscillator power amplifier.
• Comparative spectroscopic analysis of plasmas driven by 1-µm and 2-µm lasers across intensities from 0.5 to 5 × 10¹¹ W/cm².
• Measurement of EUV spectra (5.5–25.5 nm) and assessment of plasma ionicities and conversion efficiency at a 60-degree observation angle.

Main Results:

• Similar EUV spectra and plasma ionicities were observed for both laser wavelengths when the intensity ratio I_1µm/I_2µm was maintained at 2.4(7).
• A two-fold increase in conversion efficiency (CE) for 13.5 nm EUV radiation was achieved with the 2-µm laser compared to the 1-µm laser.
• Findings on optimum laser intensity scaling with wavelength were extended using existing literature data.

Conclusions:

• The 2-µm laser wavelength offers significantly higher conversion efficiency for industrial EUV generation compared to the 1-µm laser.
• Understanding wavelength scaling is vital for optimizing laser-plasma interactions and developing advanced EUV sources.
• This research provides critical insights for the development of more efficient EUV lithography and other applications.