Dr. Ehsan Alimohammadian Profile

Dr. Ehsan Alimohammadian

at Meta Materials Inc

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Publications (5)

Proceedings Article | 29 August 2022 Poster + Paper

Tunable fibre Bragg grating arrays for spectral cross-correlation

Polina Zavyalova, Suresh Sivanandam, Peter Herman, Ehsan Alimohammadian, Abdullah Rahnama

Proceedings Volume 12184, 1218458 (2022) https://doi.org/10.1117/12.2630688

KEYWORDS: Fiber Bragg gratings, Astronomy, Optical fibers, Astrophotonics

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Proceedings Article | 30 March 2021 Presentation + Paper

From filaments to light-sheets: tailoring the spectrum of fiber Bragg gratings with femtosecond lasers

Polina Zavyalova, Abdullah Rahnama, Ehsan Alimohammadian, JianZhao Li, Suresh Sivanandam, Peter Herman

Proceedings Volume 11676, 116760X (2021) https://doi.org/10.1117/12.2585179

KEYWORDS: Fiber Bragg gratings, Femtosecond phenomena, Spatial light modulators, Cladding, Beam shaping, Waveguides, Telecommunications, Structured optical fibers, Spectrometers, Refractive index

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Proceedings Article | 10 March 2020 Presentation

Harnessing femtosecond laser filaments for nano-structuring of "Lab-in-Fibre" sensors and "Spectrometer-in-Fibre" microsystems (Conference Presentation)

Peter Herman, Ehsan Alimonhammadian, Keivan Aghdami, Erden Ertorer, Young Hwan Kim, Jianzhao Li, Abdullah Rahnama

Proceedings Volume 11292, 1129202 (2020) https://doi.org/10.1117/12.2551249

KEYWORDS: Femtosecond phenomena, Sensors, Spectroscopy, Microsystems

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Proceedings Article | 21 April 2017 Presentation

Manipulating femtosecond laser interactions in bulk glass and thin-film with spatial light modulation (Conference Presentation)

Ehsan Alimohammadian, Stephen Ho, Erden Ertorer, Sebastian Gherghe, Jianzhao Li, Peter Herman

Proceedings Volume 10094, 100940Z (2017) https://doi.org/10.1117/12.2255877

KEYWORDS: Modulation, Spatial light modulators, Thin films, Femtosecond phenomena, Glasses, Beam shaping, Waveguides, Optical tracking, Spherical lenses, Plasma

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Spatial Light Modulators (SLM) are emerging as a power tool for laser beam shaping whereby digitally addressed phase shifts can impose computer-generated hologram patterns on incoming laser light. SLM provide several additional advantages with ultrashort-pulsed lasers in controlling the shape of both surface and internal interactions with materials. Inside transparent materials, nonlinear optical effects can confine strong absorption only to the focal volume, extend dissipation over long filament tracks, or reach below diffraction-limited spot sizes. Hence, SLM beam shaping has been widely adopted for laser material processing applications that include parallel structuring, filamentation, fiber Bragg grating formation and optical aberration correction.

This paper reports on a range of SLM applications we have studied in femtosecond processing of transparent glasses and thin films. Laser phase-fronts were tailored by the SLM to compensate for spherical surface aberration, and to further address the nonlinear interactions that interplay between Kerr-lens self-focusing and plasma defocusing effects over shallow and deep focusing inside the glass. Limits of strong and weak focusing were examined around the respective formation of low-loss optical waveguides and long uniform filament tracks. Further, we have employed the SLM for beam patterning inside thin film, exploring the limits of phase noise, resolution and fringe contrast during interferometric intra-film structuring.

Femtosecond laser pulses of 200 fs pulse duration and 515 nm wavelength were shaped by a phase-only LCOS-SLM (Hamamatsu X10468-04). By imposing radial phase profiles, axicon, grating and beam splitting gratings, volume shape control of filament diameter, length, and uniformity as well as simultaneous formation of multiple filaments has been demonstrated. Similarly, competing effects of spherical surface aberration, self-focusing, and plasma de-focusing were studied and delineated to enable formation of low-loss optical waveguides over shallow and deep focusing conditions.

Lastly, SLM beam shaping has been successfully extended to interferometric processing inside thin transparent film, enabling the arbitrary formation of uniform or non-uniform, symmetric or asymmetric patterns of flexible shape on nano-scale dimensions without phase-noise degradation by the SLM patterning. We present quantized structuring of thin films by a single laser pulse, demonstrating λ/2nfilm layer ejection control, blister formation, nano-cavities, and film colouring. Closed intra-film nanochannels with high aspect ratio (20:1) have been formed inside 3.5 um thick silica, opening new prospects for sub-cellular studies and lab-in-film concepts that integrate on CMOS silicon technologies.

Proceedings Article | 28 February 2014 Paper

Modeling of a CW Nd:YVO4 laser longitudinally pumped by high power VCSEL modules at 808 nm

E. Alimohammadian, A. Major

Proceedings Volume 8959, 89591D (2014) https://doi.org/10.1117/12.2036813

KEYWORDS: Crystals, Vertical cavity surface emitting lasers, Neodymium lasers, Laser crystals, Nd:YAG lasers, Output couplers, Continuous wave operation, Absorption, High power lasers, Semiconductor lasers

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