Leo A. Siiman

Coherent femtosecond pulse combining of multiple parallel chirped pulse fiber amplifiers

We report on femtosecond pulse combining with up to four parallel chirped-pulse fiber amplifier channels. Active phase locking is implemented using the LOCSET (Locking of Optical Coherence by Single-detector Electronic-frequency Tagging) single detector feedback technique, resulting in 96.4%, 94.0%, and 93.9% relative combining efficiency with two, three, and four channels respectively. Theoretical and experimental analysis of combining efficiency dependence on amplitude and phase noise shows convergence to a fixed value with increasing number of channels, indicating that multi-channel pulse combining with LOCSET feedback should be scalable to very large numbers of channels.

Femtosecond pulse spectral synthesis in coherently-spectrally combined multi-channel fiber chirped pulse amplifiers

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.

Ultrashort laser pulse diffraction by transmitting volume Bragg gratings in photo-thermo-refractive glass.

We report on the characteristics of ultrashort laser pulse diffraction by transmitting volume Bragg gratings recorded in photo-thermo-refractive glass. The angular and spectral selectivity properties of these phase volume gratings are shown to obey the predictions of a modified Kogelniks coupled wave analysis that accounts for polychromatic beams. Spatio-temporal distortions such as angular dispersion and pulse front tilt that occur after diffraction by a single volume grating are studied and corrected by using a volume grating pair. The angular filtering properties of volume gratings offer potential as spatial filtering elements inside ultrafast laser cavities.

Phase Fresnel lens recorded in photo-thermo-refractive glass by selective exposure to infrared ultrashort laser pulses

A new two-step approach for fabricating phase optical elements in photo-thermo-refractive glass by exposure to IR ultrashort laser pulses followed by thermal development is shown. A binary phase Fresnel lens was designed to focus light at 632.8 nm to a focal length of 400 cm. Conditions of ultrashort pulse irradiation and thermal development were chosen to achieve pi phase shift between zone boundaries. The focusing efficiency of the element was measured to be close to 50%.

Single-frequency and single-transverse mode Yb-doped CCC fiber MOPA with robust polarization SBS-free 511W output

We demonstrate 511W single-frequency (Δν << 40MHz), single-transverse mode and robust linear polarization output fiber MOPA based on 37µm diameter Yb-doped Chirally-Coupled-Core air-clad fiber.

Color center generation in sodium-calcium silicate glass by nanosecond and femtosecond laser pulses

It was found that high purity soda lime glass shows a markedly different induced absorption spectra when exposed to different types of ionizing radiation such as UV lamp or femtosecond and nanosecond laser pulses. The following irradiation was used in the experiments: nanosecond pulses at the fundamental and harmonics of a Nd:YAG laser (λ = 1064, 532, 355, and 266 nm), femtosecond pulses of a Ti:sapphire laser operating at λ = 780 nm, ultraviolet rays from a high pressure Xe lamp, X-rays, and Gamma rays. Features of radiation defect generations are discussed.

Femtosecond pulse coherent combining and spectral synthesis using four parallel chirped pulse fiber amplifiers

We demonstrate spectral synthesis of femtosecond pulses in a coherently combined four-channel fiber chirped pulse amplifier array. This approach offers a path to overcome gain narrowing limitations of individual fiber amplifier channels.

Non-collinear generation of third harmonic of IR ultrashort laser pulses by PTR glass volume Bragg gratings.

Three conditions for non-collinear third harmonic generation by a PTR glass volume Bragg grating are demonstrated using infrared ultrashort pulse illumination. Each condition corresponds to a different angle of grating orientation and a separate generation mechanism. We identify the mechanisms as corresponding to sum-frequency generation, Bragg diffraction of 3 omega, and a non-resonant Bragg condition involving three omega photons interacting with a nonlinear grating vector. Theoretical modeling is performed using wave vector additions and the results are compared to experimental measurements.

Femtosecond pulses from coherently combined parallel chirped pulse fiber amplifiers

Active coherent combining of femtosecond pulses from parallel chirped-pulse fiber amplifiers is demonstrated. This opens a new path for simultaneously increasing both energy and average power of ultrashort pulses from fiber based systems.

Femtosecond pulse spectral synthesis using coherently combined multi-channel fiber chirped pulse amplifiers

We synthesize femtosecond pulses by coherently combining spectra from three fiber chirped pulse amplifiers. Multi-channel spectral synthesis offers a way to overcome gain narrowing limitations in a single fiber amplifier.