Papers by Almantas Galvanauskas
ABSTRACT We present a detailed model of a multi-fiber interferometric resonator with a saturable ... more ABSTRACT We present a detailed model of a multi-fiber interferometric resonator with a saturable absorber in the output arm. The results demonstrate coherent combining and the generation of mode locked pulses.
We show stacking of multiple equal-amplitude pulses into a single pulse using properly configured... more We show stacking of multiple equal-amplitude pulses into a single pulse using properly configured sequences of Gires-Tournois interferometers, which in conjunction of chirped pulse amplification in fibers can enable large increase in extractable pulse energies.
Ultrafast Phenomena, 1994
Here we study the use of tunable three-section distributed-Bragg-reflector (DBR) diode lasers as ... more Here we study the use of tunable three-section distributed-Bragg-reflector (DBR) diode lasers as pulse sources for chirped pulse amplification (CPA) in a fiber amplifier. The broad continuous-tuning range of the laser allows the generation of nanosecond linearly chirped pulses, which are amplified in a fiber amplifier up to microjoule energies and then compressed to transform-limited subpicosecond duration. The energy of these ultrashort pulses is more than two orders of magnitude higher than any previously reported energies from a compact diode laser and fiber source.
Conference on Lasers and Electro-Optics, 2021
We show equivalence of coherent pulse stacking system to a deep recurrent neural network, and exp... more We show equivalence of coherent pulse stacking system to a deep recurrent neural network, and experimentally demonstrate real-time learning on stacking cavities and input pulses, necessary for high fidelity coherent temporal combining with ∼102 pulses.
Conference on Lasers and Electro-Optics, 2020
Small-signal parametric gain at 10.6 pm in GaSe crystal pumped at 2.75 pm is experimentally demon... more Small-signal parametric gain at 10.6 pm in GaSe crystal pumped at 2.75 pm is experimentally demonstrated. Simulation predicts that nanosecond optical parametric chirped-pulse amplification in GaSe supports sub-three-cycle pulses.
Applied Optics, Oct 25, 2018
An all-in-fiber method of generating orbital angular momentum (OAM) is proposed. A simple device ... more An all-in-fiber method of generating orbital angular momentum (OAM) is proposed. A simple device composed with a section of helically symmetric fiber and another section of regular fiber is designed to convert input light to optical vortices. Finite element method calculation of first-and second-order OAM generation based on the coordinates transformation technique is taken to show that the eigenmodes of the helically symmetric fiber structures carry orbital and spin angular momentum. Simulation using the self-developed beam propagation method algorithm is also performed to verify the orbital angular momentum generation and evaluate the performance of the OAM generator.
We report on a fibre amplifier system generating picosecond pulses with 100µJ energy. A mode-lock... more We report on a fibre amplifier system generating picosecond pulses with 100µJ energy. A mode-locked fibre oscillator is used to seed a multi-stage acousto-optically gated fibre amplifier. The final stage comprises a cladding pumped multimode Er3+/Yb3+ co-doped fibre pumped with 4 W of power at 982 nm and produces up to 250µJ pulse energy
ABSTRACT In this paper we report the first demonstration of efficient hard X-ray generation using... more ABSTRACT In this paper we report the first demonstration of efficient hard X-ray generation using a femtosecond fiber laser. The hard X-ray source has yield efficiencies similar to those obtained with solid state laser drivers with comparable pulse energies and intensities. Further experiments on increasing X-ray yield efficiency with higher pulse energies from the current system are in progress. Since this fiber laser technology is scalable to >100-W of average power this demonstration opens a path towards compact high-brightness hard X-ray sources for imaging and time resolved diffraction experiments.
We report demonstration of a new spectrally-controllable device, based on a sequence of linear po... more We report demonstration of a new spectrally-controllable device, based on a sequence of linear polarizers and birefringent plates, which allows to accurately and adjustably tailor its spectral filtering properties for achieving complete gain-narrowing compensation over ~30nm of signal bandwidth in an Yb-doped fiber system with the total gain reaching 150dB. The experimental demonstration was performed in a regenerative Yb-fiber amplifier system with controllable number of passes, allowing to characterize both signal spectral-narrowing, and as well as spectral compensation at varying levels of achieved total gain. This result opens a pathway towards 100fs duration multi-mJ pulses from fiber CPSA systems.
Proceedings of SPIE, Feb 7, 2008
Single-polarization single-transverse-mode rod-type photonic crystal fiber with mode-fieldarea of... more Single-polarization single-transverse-mode rod-type photonic crystal fiber with mode-fieldarea of 2300 µm 2 O.
IEEE Journal of Quantum Electronics, Feb 1, 2018
Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks severa... more Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy from fiber lasers. We develop a robust, scalable, and distributed digital control system with firmware and software integration for algorithms, to support the CPS application. We model CPS as a digital filter in the Z domain and implement a pulse-pattern-based cavity phase detection algorithm on an fieldprogrammable gate array (FPGA). A two-stage (2+1 cavities) 15-pulse stacking system achieves an 11.0 peak-power enhancement factor. Each optical cavity is fed back at 1.5 kHz, and stabilized at an individually-prescribed round-trip phase with 0.7 deg and 2.1 deg rms phase errors for Stages 1 and 2, respectively. Optical cavity phase control with nanometer accuracy ensures 1.2% intensity stability of the stacked pulse over 12 h. The FPGA-based feedback control system can be scaled to large numbers of optical cavities.
Femtosecond (~670 fs) fiber-CPA at 1.063 μm is demonstrated using broadband chirped-volume-Bragg-... more Femtosecond (~670 fs) fiber-CPA at 1.063 μm is demonstrated using broadband chirped-volume-Bragg-gratings for pulse stretching and compression. 32 W recompressed pulses are achieved corresponding to a 75% compression efficiency.
Applied Optics, Sep 25, 2018
An all-in-fiber method of generating orbital angular momentum (OAM) is proposed. A simple device ... more An all-in-fiber method of generating orbital angular momentum (OAM) is proposed. A simple device composed with a section of helically symmetric fiber and another section of regular fiber is designed to convert input light to optical vortices. Finite element method calculation of first-and second-order OAM generation based on the coordinates transformation technique is taken to show that the eigenmodes of the helically symmetric fiber structures carry orbital and spin angular momentum. Simulation using the self-developed beam propagation method algorithm is also performed to verify the orbital angular momentum generation and evaluate the performance of the OAM generator.
Proceedings of SPIE, Mar 22, 2013
3C fiber technology advances the performance frontier of practical, high-pulse-energy fiber laser... more 3C fiber technology advances the performance frontier of practical, high-pulse-energy fiber lasers by providing very large core fibers with the handling and packaging benefits associated with single mode fibers. First-generation fibers demonstrate scaling to > 240 W average power coincident with 100-kW peak power in 1-mJ, 10-ns pulses while maintaining single-mode beam quality, polarized output, and efficiencies > 70%. Peak powers over 0.5 MW with negligible spectral distortion can be achieved with sub ns, near-transform-limited pulses. In-development secondgeneration 3C Yb-fiber based on core sizes around 55 μm 1 have produced >8 mJ, 13 ns pulses with peak powers exceeding 600 kW.
Optics Express, Feb 8, 2013
We demonstrate coherent spectral beam combining and femtosecond pulse spectral synthesis using th... more We demonstrate coherent spectral beam combining and femtosecond pulse spectral synthesis using three parallel fiber chirped pulse amplifiers, each amplifying different ultrashort-pulse spectra. This proof-of-concept experiment opens a path to simultaneously overcome individual-amplifier energy and power limitations, as well as limitations on amplified pulse spectra due to the gain narrowing in a single fiber amplifier.
9th Int. Particle Accelerator Conf. (IPAC'18), Vancouver, BC, Canada, April 29-May 4, 2018, Jun 1, 2018
Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks severa... more Coherent pulse stacking (CPS) is a new time-domain coherent addition technique that stacks several optical pulses into a single output pulse, enabling high pulse energy and high average power. We model the CPS as a digital filter in the Z domain, and implement two deterministic algorithms extracting the cavity phase from limited data where only the pulse intensity is available. In a 2-stage 15-pulse CPS system, each optical cavity is stabilized at an individually-prescribed round-trip phase with 0.7 deg and 2.1 deg RMS phase errors for Stage 1 and Stage 2 respectively. Optical cavity phase control with nm accuracy ensures 1.2% intensity stability of the stacked pulse over 12 hours.
9th Int. Particle Accelerator Conf. (IPAC'18), Vancouver, BC, Canada, April 29-May 4, 2018, Jun 1, 2018
Coherent temporal pulse stacking combines the energy from a train of pulses into one pulse throug... more Coherent temporal pulse stacking combines the energy from a train of pulses into one pulse through a series of optical cavities. To stabilize the output energy, the cavity roundtrip phases must be precisely locked to particular values. Leveraging the LLRF expertise we have for conventional accelerators, a FPGA-based control system has been developed for optical cavity phase control. A phase measurement method, "Modulated Impulse Response", has been developed and implemented on FPGA. An experiment demonstrated that it can measure and lock the optical phases of four stacking cavities, leading to combination of 25 pulses into one pulse with 1.5 % RMS stability over 30 hours.
We have temporally combined 25 equal-amplitude pulses using four cavities, stabilizing cavity rou... more We have temporally combined 25 equal-amplitude pulses using four cavities, stabilizing cavity round-trip phase by measuring the response to a probe pulse train. Energy enhancement of 18.4 is maintained within 1% RMS.
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Papers by Almantas Galvanauskas