Evan Hale

Fibertek (United States)

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Elan D. Louis

The University of Texas Southwestern Medical Center

Ivan Divliansky

University of Central Florida

Leonid Glebov

University of Central Florida

Gina Liu

Shanghai Library

George Venus

IPG Photonics (United States)

Deepti Varathan

Yale University

Marc SeGall

University of Central Florida

Brian Anderson

Victoria University of Wellington

Christine Kim

Georgetown University

Hollie Dowd

Yale University

Cooperative Institutions

University of Central Florida

Photonics (United States)

Fibertek (United States)

University of Michigan–Ann Arbor

Lawrence Livermore National Laboratory

Friedrich Schiller University Jena

Yale University

Columbia University

Helmholtz Institute Jena

Fraunhofer Institute for Applied Optics and Precision Engineering

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Higher order mode selection for power scaling in laser resonators using transmitting Bragg gratings

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2015)

Brian Anderson George Venus Dan Ott Evan Hale Ivan Divliansky

Power scaling using a higher order mode in a ribbon fiber has previously been proposed. However, methods of selecting the higher order mode and converting to a single lobe high brightness beam are needed. We propose using a multiplexed transmitting Bragg grating (MTBG) to convert a higher order mode into a single lobe beam. Using a ribbon fiber with core dimensions of 107.8 μm by 8.3 μm, we use the MTBG to select a higher order mode oscillating within the resonator with 51.4% efficiency, while simultaneously converting the higher order mode to a beam with diffraction limited divergence of 10.2 mrad containing 60% of the total power.

Fiber Bragg Grating

Ribbon

Beam divergence

10.1117/12.2177060

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Citations (1)

Under-Recognition of Cervical Dystonia: An Essential Tremor Patient with Numerous Textbook Features of Cervical Dystonia.

PubMed (2019)

Evan Hale Gina Liu Christine Kim Elan D. Louis

Physical examination findings of dystonia are often underrecognized, especially in the setting of other movement disorders such as essential tremor (ET).A patient with ET exhibited numerous textbook features of cervical dystonia, which were misattributed to ET by a primary care physician and two neurologists.To provide a clear and unmistakable visual example of the clinically significant characteristics of cervical dystonia in the setting of concomitant ET.

Cervical dystonia

Concomitant

Movement Disorders

10.7916/tohm.v0.733

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Citations (3)

Severe Essential Tremor: Illustrative Videos

Tremor and Other Hyperkinetic Movements (2019)

Evan Hale Elan D. Louis

Background: Essential tremor (ET) can be profoundly disabling in severe cases; however, such cases may not often be encountered by general practitioners, primary care physicians, or general neurologists, leading to misdiagnosis. Phenomenology shown: Severe kinetic, postural, and intention tremors in patients with ET. Educational value: To provide visual examples of severe, long-standing ET for general practitioners, primary care clinicians, and general neurologists.

General hospital

10.5334/tohm.517

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Citations (3)

High brightness sub-nanosecond Q-switched laser using volume Bragg gratings

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2016)

Brian Anderson Evan Hale George Venus Daniel Ott Ivan Divliansky

The design of Q-switched lasers capable of producing pulse widths of 100's of picoseconds necessitates the cavity length be shorter than a few centimeters. Increasing the amount of energy extracted per pulse requires increasing the mode area of the resonator that for the same cavity length causes exciting higher order transverse modes and decreasing the brightness of the output radiation. To suppress the higher order modes of these multimode resonators while maintaining the compact cavity requires the use of intra-cavity angular filters. A novel Q-switched laser design is presented using transmitting Bragg gratings (TBGs) as angular filters to suppress the higher order transverse modes. The laser consists of a 5 mm thick slab of Nd:YAG, a 3 mm thick slab of Cr:YAG with a 20% transmission, one TBG aligned to suppress the higher order modes along the x-axis, and a 40% output coupler. The gratings are recorded in photo-thermo-refractive (PTR) glass, which has a high damage threshold that can withstand both the high peak powers and high average powers present within the resonator. Using a 4.1 mrad TBG in a 10.8 mm long resonator with an 800μm x 400 μm pump beam, a nearly diffraction limited beam quality of M² = 1.3 is obtained in a 0.76 mJ pulse with a pulse width of 614 ps.

Output coupler

Q-switching

Optical cavity

Nanosecond

10.1117/12.2212660

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Development of a frequency-locked Er:YAG laser for methane and water vapor DIAL

Nathan Harkema Evan Hale T. E. Moore Travis Jones Mary Erfani

Information on the spatial distributions of methane and vertical profiles of water vapor are essential in better understanding the carbon cycle, atmospheric dynamics and their roles in climate change and numerical weather prediction. Fibertek is developing Er:YAG laser technology for differential absorption lidar (DIAL) that can simultaneously access methane (1645.55 nm) and water vapor (822.92 nm) absorption lines. In this paper we will present data on a hardened 1kHz single-frequency oscillator that is frequency doubled to produce 3 mJ at 823 nm and 3 mJ at 1645 nm for airborne DIAL on the NASA Langley HALO platform. Status and challenges addressed in power scaling experiments on the Er:YAG system for a space-based mission will also be presented. Finally, we will present small signal gain measurements in Er:YAG which show the benefits of low temperature operation for power scaling.

Dial

Sulfur hexafluoride

Frequency Conversion

10.1117/12.3002925

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Novel Solid State Lasers Based on Volume Bragg Gratings

Evan Hale

Source

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Post-stroke sleep disturbance and recurrent cardiovascular and cerebrovascular events: A systematic review and meta-analysis

Sleep Medicine (2023)

Evan Hale Elie Gottlieb John Usseglio Ari Shechter

Stroke

Positive airway pressure

Sleep study

10.1016/j.sleep.2023.02.019

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Citations (23)

Characterization of laser diodes under short-pulsed conditions with high pulse energies

Proceedings of SPIE, the International Society for Optical Engineering/Proceedings of SPIE (2013)

Tobias Koenning Evan Hale David Irwin Kim Alegria Steve Patterson

New applications require diode lasers to be driven with short pulses in the sub-micro second range. The goal is to minimize both the cost and size of the diode laser module by minimizing the number of laser bars required while maintaining the lifetime that is desired for the application. Products demanded by the market using such short pulses range from QCW stacks to fiber coupled modules. While many short pulsed applications use high fill factor bars, these bars are not suited for high brightness applications or coupling into small fiber cores. The focus of this work is the analysis of CW diode designs commonly used for high brightness fiber coupled modules under short pulsed conditions. Three key parameters need to be known in order to design a diode laser module that is suited for high peak powers. First is the damage threshold of the facet. The damage threshold determines the maximum power level at which the laser can be operated safely, considering a proper safety margin dependent on application. The damage threshold is a function of the input pulse width and amplitude. The second parameter which is influenced by the drive current is the slow axis divergence of the diode laser. Knowledge of this parameter is critical when designing the system optics. The third parameter is the effective emitter size which may increase with operating current. An increase in emitter size will lead to larger divergences after collimating optics for a given focal length lens and may result in a larger spot when coupling into an optical fiber. All these parameters have to be considered when designing a new product. Presented here is a study on these three critical parameters as a function of operating conditions. Results for different diode designs will be presented. The data presented includes damage thresholds, as well as near field and far field data at various operating currents. A design study for fiber coupled modules with high pulse energies based on the test results will be shown for various wavelengths.

Collimated light

Laser diode

Beam divergence

10.1117/12.2005059

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Citations (2)

Are cerebellar signs seen in pre-manifest essential tremor cases? A study of unaffected first-degree relatives of cases (1089)

Neurology (2020)

Elan D. Louis Evan Hale Hollie Dowd Gina Liu Deepti Varathan

Thursday, April 30April 14, 2020Free AccessAre cerebellar signs seen in pre-manifest essential tremor cases? A study of unaffected first-degree relatives of cases (1089)Elan Louis, Evan Hale, Hollie Dowd, Gina Liu, and Deepti VarathanAuthors Info & AffiliationsApril 14, 2020 issue94 (15_supplement)https://doi.org/10.1212/WNL.94.15_supplement.1089 Letters to the Editor

Thursday

First-degree relatives

10.1212/wnl.94.15_supplement.1089

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Citations (0)

Wavefront shaping optical elements recorded in photo-thermo-refractive glass

Applied Optics (2019)

Ivan Divliansky Fedor Kompan Evan Hale Marc SeGall Axel Schülzgen

The paper presents an overview of the benefits of recording phase masks into the bulk of photo-thermo-refractive glass. We demonstrate that both binary and gray-scale phase masks can be encoded into the medium, and that such masks can be used for mode conversion and beam shaping with near-theoretical efficiency. We further demonstrate that by encoding the phase mask profile into a transmitting volume Bragg grating, it is possible to create tunable and achromatic phase masks without requiring a complex phase pattern.

Achromatic lens

Light beam

10.1364/ao.58.000d61

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Citations (6)