Single shot M2 measurement for near infrared high energy laser pulses

Siva Sankar Nagisetty; Taisuke Miura; Martin Smrz; Vaclav Kubecek; Akira Endo; Tomáš Mocek

doi:10.1117/12.2079669

3 March 2015 Single shot M² measurement for near infrared high energy laser pulses

Siva Sankar Nagisetty, Taisuke Miura, Martin Smrz, Vaclav Kubecek, Akira Endo, Tomáš Mocek

Proceedings Volume 9343, Laser Resonators, Microresonators, and Beam Control XVII; 93431F (2015) https://doi.org/10.1117/12.2079669
Event: SPIE LASE, 2015, San Francisco, California, United States

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.

Citation Download Citation

Siva Sankar Nagisetty, Taisuke Miura, Martin Smrz, Vaclav Kubecek, Akira Endo, and Tomáš Mocek "Single shot M² measurement for near infrared high energy laser pulses", Proc. SPIE 9343, Laser Resonators, Microresonators, and Beam Control XVII, 93431F (3 March 2015); https://doi.org/10.1117/12.2079669

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KEYWORDS

Cameras

Laser beam propagation

Glasses

Optical testing

Pulsed laser operation

Time metrology

Luminescence

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