Shih-Hsuan Chia

Toward Waveform Nonlinear Optics Using Multimillijoule Sub-Cycle Waveform Synthesizers

Waveform nonlinear optics aims to study and control the nonlinear interactions of matter with extremely short optical waveforms custom-tailored within a single cycle of light. Different technological routes to generate such multimillijoule sub-optical-cycle waveforms are currently pursued, opening up unprecedented opportunities in attoscience and strong-field physics. Here, we discuss the experimental schemes, introduce the technological challenges, and present our experimental results on high-energy sub-cycle optical waveform synthesis based on (1) parametric amplification and (2) induced-phase modulation in a two-color-driven gas-filled hollow-core fiber compressor. More specifically, for (1), we demonstrate a carrier-envelope-phase (CEP)-stable, multimillijoule three-channel parametric waveform synthesizer generating a >2-octave-wide spectrum (0.52-2.4 μm). After two amplification stages, the combined 125-μJ output supports 1.9-fs FWHM waveforms; energy scaling to >2 mJ is achieved after three amplification stages. FROG pulse characterization of all three second-stage outputs demonstrates the feasibility to recompress all three channels simultaneously close to the Fourier limit and shows the flexibility of our intricate dispersion management scheme for different experimental situations. For (2), we generate CEP-stable 1.7-mJ waveforms covering 365-930 nm (measured at 1% of the peak intensity) obtained from induced-phase modulation in a two-color-driven gas-filled hollow-core fiber. Using custom-designed double-chirped mirrors and a UV spatial light modulator will permit compression close to the 0.9-fs FWHM transform limit. These novel sources will become versatile tools for controlling strong-field interactions in matter and for attosecond pump-probe spectroscopy using VIS/IR and XUV/soft-X-ray pulses.

Energetic ultrafast fiber laser sources tunable in 1030–1215 nm for deep tissue multi-photon microscopy

We demonstrate an energy scalable approach to implement ultrafast fiber laser sources suitable for deep tissue multi-photon microscopy imaging. Enabled by fiber-optic nonlinearities (dominated by self-phase modulation), these unique ultrafast sources produce nearly transform-limited pulses of 50-90 fs in duration with the center wavelength tunable in the wavelength range of 1030-1215 nm. The resulting pulse energy can be scaled up to 20 nJ by optimizing fiber dispersion, shortening fiber length, and using large-mode-area fibers. We applied such an energetic source to a proof-of-principle study of ex vivo human skin based on harmonics (i.e., second-harmonic generation and third-harmonic generation) imaging. This new type of fiber-format energetic ultrafast source provides a robust solution for multiphoton microscopy applications.

Multi-mJ parametric synthesizer generating two-octave-wide optical waveforms

We demonstrate a phase-stable, multi-mJ 3-channel parametric synthesizer generating a 2-octave-wide spectrum (0.52-2.4μm). After two amplification stages, the combined 125-μJ output supports 1.9-fs waveforms. Energy scaling to 2 mJ is achieved after three amplification stages.

Spectro-Temporal Characterization of All Channels in a Sub-Optical-Cycle Parametric Waveform Synthesizer

We present FROG characterization of all three amplification channels of a two-stage sub-optical-cycle parametric waveform synthesizer covering more than two octaves in bandwidth. A flexible dispersion compensation scheme will permit compression at the multi-mJ level.

Jitter analysis of timing-distribution and remote-laser synchronization systems

We present a powerful jitter analysis method for timing-distribution and remote-laser synchronization systems based on feedback flow between setup elements. We synchronize two different mode-locked lasers in a master-slave configuration locally and remotely over a timing-stabilized fiber link network. Local synchronization reveals the inherent jitter of the slave laser as 2.1 fs RMS (>20 kHz), whereas remote synchronization exhibits an out-of-loop jitter of 8.55 fs RMS integrated for 1 Hz - 1 MHz. Our comprehensive feedback model yields excellent agreement with the experimental results and identifies seven uncorrelated noise sources, out of which the slave lasers jitter dominates with 8.19 fs RMS.

High-Energy Carrier-Envelope Phase-Stable Optical Waveforms Compressible to <1 fs Using Induced-Phase Modulation in Argon-Filled Hollow-Core Fiber

We demonstrate phase-stable, ~0.4-mJ optical waveforms based on induced-phase modulation for generating sub-fs optical pulses. Using custom-designed double-chirped mirrors and spatial light modulator, such optical waveforms will become a versatile tool for strong-field attoscience.

40-µJ passively CEP-stable seed source for ytterbium-based high-energy optical waveform synthesizers.

We demonstrate experimentally for the first time a ~40-µJ two-octave-wide passively carrier-envelope phase (CEP)-stable parametric front-end for seeding an ytterbium (Yb)-pump-based, few-optical-cycle, high-energy optical parametric waveform synthesizer. The system includes a CEP-stable white-light continuum and two-channel optical parametric chirped pulse amplifiers (OPCPAs) in the near- and mid-infrared spectral regions spanning altogether a two-octave-wide spectrum driven by a regenerative amplifier. The output pulses are compressed and fully characterized to demonstrate the well-behaved spectral phase of this seed source.

Broadband continuum generation in mode-locked lasers with phase-matched output couplers

The concept of intracavity phase matching is proposed and demonstrated both theoretically and experimentally with a broadband phase-matched dielectric output coupler for linear-cavity few-cycle Ti:sapphire oscillators. The spectrum in the matched wavelength range is enhanced by >10  dB while maintaining good beam quality via resonantly enhanced continuum generation. The enhanced spectral components can be continuously tuned by varying the intracavity dispersion. Because dielectric coatings offer flexible design capabilities, this approach is applicable to various lasers with different gain media to obtain custom-tailored spectra, which have the potential to benefit several applications, such as shorter pulse generation, seeding of ytterbium lasers for pumping optical parametric amplifiers, and direct f-2f detection of the carrier-envelope phase.

Above-Millijoule Optical Waveforms Compressible to Sub-fs Using Induced-Phase Modulation in a Neon-Filled Hollow-Core Fiber

We demonstrate 1.7-mJ optical waveforms based on induced-phase modulation for generating sub-femtosecond optical pulses. Using custom-designed double-chirped mirrors and a spatial light modulator, such optical waveforms will become a versatile tool for strong-field attoscience.

High Energy Sub-cycle Optical Waveform Synthesizer

High-energy sub-cycle optical waveform synthesis is demonstrated with a three-channel OPA pumped by an 18-mJ cryogenically cooled Ti:sapphire laser. The system aims towards multi-mJ, 2-fs, phase-stable pulses covering the wavelength range from 0.52 - 2.4µm