Dr. Alok Kumar Pandey Profile

Dr. Alok Kumar Pandey

at Imagine Optic SA

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Author

Publications (5)

Proceedings Article | 11 April 2024 Poster

Experimental investigation of nonlinear ionization of transparent dielectrics exposed to single-shot ultrashort laser excitation

Olivier Uteza, Thibault Genieys, Julia Ferrer-Ortas, Alok Pandey, Nicolas Sanner

Proceedings Volume PC12939, PC129391P (2024) https://doi.org/10.1117/12.3012759

KEYWORDS: Dielectrics, Ionization, Ultrafast phenomena, Laser ablation, Silica, Plasma, Optical properties, Micromachining, Femtosecond phenomena, Transform theory

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Non-linear ionization is the physical excitation mechanism by which an ultrashort laser locally transforms a dielectric from an initial insulating to a highly conductive state with considerable changes on its local electrical and optical properties. When controlled, this local excitation of the material yields well-calibrated macroscopic post-mortem transformation on which every optimized process of laser micromachining builds on. The work presented here is part of this perspective to get control of such laser-induced transformation, aiming to propose an accurate experimental evaluation of laser energy deposition at the surface of a dielectric material exposed to ultrashort pulses, and in particular of its produced free-electron – hole plasma density. For that objective, we conceive appropriate single-shot energy balance experiments with specifically designed dielectric targets consisting of wedged and plane-parallel samples of different thickness (below and above the Rayleigh of the focused laser) in order to observe the free-electron hole plasma produced at the dielectric front surface and also to act on the ratio between photo-ionization and total beam losses. Experiments consists in measuring the incident, reflected and transmitted energy on a wide range of incident fluence (<< Fth to ~ Fth, where Fth indicates the laser-induced ablation threshold) by means of calibrated and identical photodiodes in order to establish a precise energy balance of the interaction. We choose fused silica material because of its popularity for micromachining and photonics applications and we also use ultrashort femtosecond pulses ( 15 - 100 fs, 800 nm) to vary the photo-ionization rate and to well decorrelate ionization process from hydrodynamics and any energy transfer and recombination processes. The information retrieved from these experiments and further confronted to Drude-Lorentz theoretical framework helps us understanding ionization processes (photo-ionization, impact ionization) and their respective importance for dielectric macroscopic transformation in the ablation regime.

Proceedings Article | 8 June 2023 Presentation + Paper

Amplification of HOH carrying orbital angular momentum in plasma-based amplifiers

Santiago López, Agustín Alonso, Elena de la Fuente, Alok Kumar Pandey, Olivier Guilbaud, Eduardo Oliva

Proceedings Volume 12582, 1258202 (2023) https://doi.org/10.1117/12.2665543

KEYWORDS: Plasmas, Krypton, Refraction, Angular momentum, Modal decomposition, Waveguides, Extreme ultraviolet, Distortion, Simulations, Polarization

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Proceedings Article | 8 June 2023 Presentation

Extreme ultraviolet vector-vortex beams from laser high order harmonic generation

Olivier Guilbaud, Alok-Kumar Pandey, Alba De Las Heras Munoz, Julio San Román, Francisco Javier Serrano Rodriguez, Elsa Baynard, Moana Pittman, Guillaume Dovillaire, Luis Plaja, Charles Durfee, Sophie Kazamias, Carlos Hernández García

Proceedings Volume PC12582, PC1258209 (2023) https://doi.org/10.1117/12.2666752

KEYWORDS: Extreme ultraviolet, Harmonic generation, Polarization, Spiral phase plates, Wavefronts, Short wave infrared radiation, Infrared radiation, X-ray lasers, Wavefront sensors, Wave propagation

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Proceedings Article | 8 July 2021 Open Access

Solid-target seeded soft X-ray laser for short pulses and optical vortex amplification

Olivier Guilbaud, Alok-Kumar Pandey, Elsa Baynard, Irene papagiannouli, Fabrice Sanson, Julien Demailly, Sophie Kazamias, Moana Pittman, Olivier Neveu, Bruno Lucas, Annette Calisti, Andrea Le Marec, Annie Klisnick, Olivier Larroche, F. Harms, G. Beaugrand, G. Dovillaire, Ph. Balcou, David Ros

Proceedings Volume 11886, 118860B (2021) https://doi.org/10.1117/12.2593356

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Proceedings Article | 8 July 2021 Open Access

Single-shot wavefront characterization of high topological charge extreme-ultraviolet vortex

A. K. Pandey, O. Guilbaud, F. Sanson, I. Papagiannouli, A. Kabacinski, F. Tissandier, F. Harms, G. Beaugrand, G. Dovillaire, E. Baynard, J. Demailly, B. Lucas, O. Neveu, M. Pittman, D. Ros, S. Sebban, Ph. Balcou, S. Kazamias

Proceedings Volume 11886, 118860L (2021) https://doi.org/10.1117/12.2592326

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