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Proceedings Paper

Single shot M2 measurement for near infrared high energy laser pulses
Author(s): Siva Sankar Nagisetty; Taisuke Miura; Martin Smrz; Vaclav Kubecek; Akira Endo; Tomáš Mocek
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Paper Abstract

Since the principle of M2 measurement is to scan the beam discretely along with propagation direction, measurement time of several minutes is required which is not suitable for pulsed lasers. Several single-shot techniques have been proposed to measure M2 by using diffraction gratings and wavefront sensor, but were shown to be more complex and yield inaccurate results for multimode beams. Another approach to measure the M2 uses Rayleigh scattering from gas or liquid-filled cell. The scattered image by laser light in the cell, however, contains lots of speckle patterns which degrade the accuracy of M2 measurement. We developed a single shot M2 measurement based on a photosensitive glass. The measurement system consists of the photosensitive glass plate and the imaging camera with macro lens. When the pulsed laser beam focused into the cross-sectional direction of photosensitive glass plate, the visible fluorescence of the glass plate indicates the focusing property of laser beam. Then the visualized beam propagation in the glass is imaged precisely to measure the beam diameters around beam waist. Since the coherent laser beam is converted to the incoherent fluorescence, the beam propagation image is free from speckle patterns. The M2 can be calculated from the image within less than a second. This simple technique allows the possibility of the real time monitoring of the beam quality. We obtained M2=1.10 from a fiber coupled diode laser that is close to the actual value of M2=1.18 using the standard scanning method.

Paper Details

Date Published: 3 March 2015
PDF: 8 pages
Proc. SPIE 9343, Laser Resonators, Microresonators, and Beam Control XVII, 93431F (3 March 2015); doi: 10.1117/12.2079669
Show Author Affiliations
Siva Sankar Nagisetty, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Czech Technical Univ. in Prague (Czech Republic)
Taisuke Miura, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Martin Smrz, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Vaclav Kubecek, Czech Technical Univ. in Prague (Czech Republic)
Akira Endo, Institute of Physics of the ASCR, v.v.i. (Czech Republic)
Tomáš Mocek, Institute of Physics of the ASCR, v.v.i. (Czech Republic)


Published in SPIE Proceedings Vol. 9343:
Laser Resonators, Microresonators, and Beam Control XVII
Alexis V. Kudryashov; Alan H. Paxton; Vladimir S. Ilchenko; Lutz Aschke; Kunihiko Washio, Editor(s)

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