High-sensitivity ultrashort mid-infrared pulse characterization by modified interferometric field autocorrelation.

We report on spectral phase retrieval of 43 MHz, ∼100 fs, 3.3 µm pulses at energies down to 8.9 pJ by a modified interferometric field autocorrelation method. The simple setup consists of a Michelson interferometer, a 266 µm thick AgGaSe2 crystal, and a homemade spectrometer with an InGaAs point detector, which is readily applicable to measuring a 20 fs (1.8 cycles) pulse at 3.3 µm. The feasibility is verified by comparing with the results obtained by simulation and frequency-resolved optical gating for the spectral phase modulation because of a 4 mm thick germanium plate.

Compact optical function generator.

We demonstrate the use of a nonlinear photonic crystal to generate a harmonic comb and an ultrabroad-band acousto-optic modulator for the field amplitudes and phases of the comb to succeed in synthesizing femtosecond and subfemtosecond optical field waveforms. Nonsinusoidal fields of various shapes are synthesized and verified using shaper-assisted linear cross-correlation. The compact all-solid-state system could lead to the realization of a portable arbitrary optical waveform synthesizer that is analogous in many aspects to an RF function generator.

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

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.

Controlling the carrier-envelope phase of Raman-generated periodic waveforms.

We demonstrate control of the carrier-envelope phase of ultrashort periodic waveforms that are synthesized from a Raman-generated optical frequency comb. We generated the comb by adiabatically driving a molecular vibrational coherence with a beam at a fundamental frequency plus its second harmonic. Heterodyne measurements show that full interpulse phase locking of the comb components is realized. The results set the stage for the synthesis of periodic arbitrary waveforms in the femtosecond and subfemtosecond regimes with full control.

Sub-single-cycle optical pulse train with constant carrier envelope phase.

We describe the synthesis of periodic waveforms consisting of a train of pulses that are 0.83 cycles long and have an electric field pulse width of 0.44 fs using 7 Raman sidebands generated by molecular modulation in H2. We verify by optical correlation that the carrier-envelope phase is constant in these waveforms when they are synthesized from commensurate sidebands. The estimated overall shift of the carrier-envelope phase is less than 0.18 cycles from the first to the last pulse of nearly 10(6) pulses in the pulse train.