Chien-Jen Lai

Synthesis and measurement of ultrafast waveforms from five discrete optical harmonics.

Optical fields have been manipulated like radio frequencies into sawtooth and square-wave patterns. Achieving the control of light fields in a manner similar in sophistication to the control of electromagnetic fields in the microwave and radiofrequency regimes has been a major challenge in optical physics research. We manipulated the phase and amplitude of five discrete harmonics spanning the blue to mid-infrared frequencies to produce instantaneous optical fields in the shape of square, sawtooth, and subcycle sine and cosine pulses at a repetition rate of 125 terahertz. Furthermore, we developed an all-optical shaper-assisted linear cross-correlation technique to retrieve these fields and thereby verified their shapes and confirmed the critical role of carrier-envelope phase in Fourier synthesis of optical waveforms.

Generation of multi-octave-spanning laser harmonics by cascaded quasi-phase matching in a monolithic ferroelectric crystal

We report the generation of the second to the sixth harmonics of a fundamental frequency covering two and a half octaves in a multiply-periodically poled lithium tantalate crystal by cascaded quasi-phase-matched frequency mixing. A frequency comb that is composed of these harmonics will permit the synthesis of a train of periodic subcycle subfemtosecond pulses in a compact setting.

Optical interference in nonlinear photonic crystals.

A model to analyze the interaction of the parametric fields being generated in a two-dimensional nonlinear photonic crystal has been developed. The analysis provides details of the interference of the generated wave(s) both inside and in the region just outside the crystal. The results are verified by second-harmonic generation in a LiNbO3 crystal that has been poled with a tetragonal inverted domain structure.

Pulse shaper assisted characterization of single-cycle optical pulses

Shaper-assisted autocorrelation is developed to characterize single-cycle pulses. The correlation signal show significantly improved signal-to-noise ratio and thus accuracy in pulse characterization when compared to cross-correlation obtained by splitting the spectral components of the pulse.

Full control of the carrier-envelope phase of Raman-generated single-cycle waveforms

Precise control of the carrier-envelope phase of Raman genearated ultrashort pulses is achieved by generating a Raman frequency comb using an infrared laser pulse and its second harmonic to drive the Raman coherence.

Synthesis and measurement of ultrafast optical waveforms

Periodic femtosecond and subfemtosecond optical waveforms whose instantaneous electric fields are shaped in the form of sawtooth, square, or sub-cycle cosine and sine pulses are synthesized and are verified by a novel correlation technique.

Synthesis and Characterization of Optical Field Waveform

Periodic optical fields in the shapes of sawtooth, square, single-cycle sine and cosine are synthesized from laser harmonics generated by molecular modulation and measured using shaper-assisted cross-correlation.

Carrier-envelope-phase control of ultrashort periodic pulses synthesized from raman generated combs

The carrier-envelope phase of Raman generated ultrashort pulses is controlled by driving the Raman coherence with a beam at near the raman resonance frequency and its second harmonic.

Optical interference in nonlinear photonic crystals

We report a generalized quantitative analysis of the origin of optical interference in two-dimensional nonlinear photonic crystals. The results are verified by a second harmonic generation experiment in a 2-D periodically-poled LiNbO3 crystal.