title: Wavefront measurement of single-mode quantum cascade laser beam for seed application in laser-produced plasma extreme ultraviolet system.
abstract: Quantum cascade laser (QCL) is a very attractive seed source for a multikilowatt pulsed CO2 lasers applied for driving extreme ultraviolet emitting plasmas. In this Letter, we investigate output beam properties of a QCL designed to address P18 and P20 lines of 10.6 micron band of CO2 molecule. In particular, output beam quality and stability are investigated for the first time. A well-defined linear polarization and a single-mode operation enabled a use of phase retrieval method for full description of QCL output beam. A direct, multi-image numerical phase retrieval technique was developed and successfully applied to the measured intensity patterns of a QCL beam. Very good agreement between the measured and reconstructed beam profiles was observed at distances ranging from QCL aperture to infinity, proving a good understanding of the beam propagation. The results also confirm a high spatial coherence and high stability of the beam parameters, the features expected from an excellent seed source.
authors.affiliation: Gigaphoton Inc., 400 Yokokura Shinden, Oyama 323-8558, Japan. kroptics@gmail.com
authors.forename: Krzysztof M
authors.initials: KM
authors.lastname: Nowak
authors.forename: Takeshi
authors.initials: T
authors.lastname: Ohta
authors.forename: Takashi
authors.initials: T
authors.lastname: Suganuma
authors.forename: Toshio
authors.initials: T
authors.lastname: Yokotsuka
authors.forename: Junichi
authors.initials: J
authors.lastname: Fujimoto
authors.forename: Hakaru
authors.initials: H
authors.lastname: Mizoguchi