Chia-Lun Tsai

Erbium Fiber Oscillator With an Intracavity Pulse Shaper for High-Energy Low-Pedestal Wavelength-Tunable Femtosecond Pulse Generation

An erbium fiber oscillator with dominating gain fiber length and an intracavity pulse shaper is experimentally demonstrated. The Kerr nonlinear phase shift induced in the fibers is suppressed by the pulse shaper, enabling high-energy (8.9 nJ) high-compression efficiency (93%) pulses of less than 270 fs duration (after linear dechirping) at modest (320 mW) pump power. A stably mode-locked spectrum corresponding to 19 nJ, 83 fs transform-limited pulse is achieved at 720 mW pump power. Wave-breaking-free pulse energy can be further enhanced by introducing stronger spectral phase modulation via the pulse shaper if more pump budget is available. We also demonstrate manipulation of the central wavelength and bandwidth of the output pulse by intracavity spectral amplitude modulation via the pulse shaper.

31 nJ sub-200 fs pulse generation from an Erbium-doped fiber amplifier similariton oscillator

We demonstrated the highest femtosecond pulse energy from Erbium-doped fiber similariton or dissipative soliton oscillators (to our best knowledge). The output spectrum can be manipulated by waveplates and filter to support 86 fs transform-limited pulse.

Phase-matching spectral phase measurement and domain period reconstruction of aperiodic quasi-phase matched gratings by nonlinear spectral interferometry

We experimentally measured the phase-matching spectral phases of aperiodic quasi-phase matched gratings for the first time (to the best of our knowledge) by nonlinear spectral interferometry. The retrieved information is useful in determining the temporal shape of the nonlinearly converted ultrafast signal and reconstructing the slowly-varying domain period distribution. The method is nondestructive, fast, sensitive, accurate, and applicable to different nonlinear materials. Compared to taking microscopic images of the etched crystal surface, our method can directly measure the domain period distribution in the crystal interior and is free of the artificial random duty period error due to image concatenation.

Generation of octave-spanning intense supercontinuum from Yb:Doped solid-state lasers in multiple thin plates

Most few-cycle pulses are formed by compression of an ultrabroadband light source obtained in meter-long hollow-core fiber filled with noble gas [1]. However, the hollow-core fiber scheme requires a careful alignment and is extremely sensitive to the beam-pointing direction, limiting its long-term stability. Recently we reported a novel approach of using a set of plates for continuum generation (MPC, schematic is shown in fig. 1(a)) using 800 nm 28 fs pulses [2]. In this paper, we present a MPC generation scheme for driving with 1030 nm lasers that have pulse duration of as long as 170 fs. We demonstrate a spectrum spanning from 550 nm to 1250 nm, (bandwidth at −20 dB intensity) that is capable of supporting single-cycle pulses while maintaining good output beam quality.

Broadband mid-infrared polarization rotator based on optically addressable LCs.

This work proposes a mid-infrared polarization rotator that incorporates a twisted nematic liquid crystal (TNLC) cell with a photo-controllable alignment layer. The TNLC device with a sufficient phase retardation can act as an achromic polarization rotation device over a wide wavelengths range and thus can rotate the polarization of a mid-IR laser beam. The photo-alignment technique enables TNLCs with arbitrary twisting angles to be generated by the use of visible polarized addressing light to control the directors of the photo-alignment layer. Therefore, arbitrary rotation angles of the polarization axis of a linearly polarized mid-IR laser beam can be realized. Moreover, the rewritable property and reliability of this polarization rotator are experimentally verified. The flexibility of polarization control for broadband mid-IR opens up a large range of potential mid-IR applications.

Intense coherent supercontinuum via IR pulse propagation in multiple thin plates

We report on the coherent supercontinuum produced by ultra-fast IR pulses propagating through thin plates. The −20 dB supercontinuum spans from 750 to 1650 nm and has a total energy of 100 uJ.

Femtosecond Erbium-doped fiber oscillator with pulse energy up to 58 nJ

Mode-locked Erbium fiber oscillator with pulse energy up to 58 nJ is experimentally demonstrated, the highest value to our best knowledge. The broadest spectrum corresponds to a transform-limited pulse of 93 fs duration.

Two-photon excited ReaChR by a three-stage femtosecond optical parametric amplifier

A three-stage optical parametric amplifier is built to produce 1 kHz, 31 fs, ~200 μJ signal pulses with tunable wavelengths. Red-activatable channelrhodopsin in fruit fly is optimally two-photon excited to copulation behavior at 1250 nm.

Generation of 30 mW CW ultraviolet by a two-path geometry for cascaded χ (2) processes with periodically poled lithium niobate crystals

30 mW continuous wave ultraviolet radiation is generated via a two-path geometry for cascaded frequency doubling and sum-frequency generation (SFG) at 18.9 W pump, where SFG is enabled by a third-order periodically poled MgO:LiNbO3.

Measurements of phase-matching spectral phase and domain period distribution by nonlinear spectral interferometry

Phase-matching spectral phases of aperiodic quasi-phase matched gratings are experimentally measured by nonlinear spectral interferometry and microscopic images, respectively. The former enables accurate reconstruction of domain length distributions with 810-μm resolution.