Milliwatt-peak-power pulse characterization at 1.55 microm by wavelength-conversion frequency-resolved optical gating

All-fiber frequency-resolved optical gating pulse characterization from chalcogenide glass

We report, to the best of our knowledge, the first all-fiber frequency-resolved optical gating device from nonlinear processing in chalcogenide glass. The strong four-wave mixing efficiency of an 11 cm long chalcogenide microwire enables a high sensitivity characterization of pulses in the 2 μm wavelength band. The amplitude and phase of chirped and unchirped picosecond pulses are accurately characterized with a high sensitivity of 0.16  mW².

Frequency-resolved optical gating technique for retrieving the amplitude of a vibrational wavepacket

We propose a novel method to determine the complex amplitude of each eigenfunction composing a vibrational wavepacket of / molecular ions evolving with a ~10 fs time scale. We find that the two-dimensional spectrogram of the kinetic energy release (KER) of H⁺/D⁺ fragments plotted against the time delay of the probe pulse is equivalent to the spectrogram used in the frequency-resolved optical gating (FROG) technique to retrieve the complex amplitude of an ultrashort optical pulse. By adapting the FROG algorithm to the delay-KER spectrogram of the vibrational wavepacket, we have successfully reconstructed the complex amplitude. The deterioration in retrieval accuracy caused by the bandpass filter required to process actual experimental data is also discussed.

Highly sensitive ultrafast pulse characterization using hydrogenated amorphous silicon waveguides

We experimentally demonstrate frequency resolved optical gating (FROG) via four-wave mixing (FWM) in ultrahigh nonlinearity hydrogenated amorphous silicon waveguides. We demonstrate FROG characterization using a FWM architecture that mimics second harmonic generation (SHG) FROG for pulsewidths as low as 360 fs. Additionally, we demonstrate for the first time a FWM architecture analogous to third harmonic generation (THG) FROG and validate its ability to overcome the direction of time ambiguity of the SHG-like architecture. Both architectures allow for sensitivities suitable for future telecommunications signals.

Combined frequency conversion and pulse compression in nonlinear tapered waveguides

We suggest an application of pump-degenerate four-wave mixing process in tapered waveguides for generation of ultrashort pulses with central frequency tunable over the material transparency range. Our method can produce strongly compressed frequency-converted pulses in presence of group-velocity mismatch and group-velocity dispersion. Additionally, the proposed technique does not require pulse phase synchronization and effectively operates for strongly chirped pump pulses, thus enabling the use of longer nonlinear media for high conversion efficiency.

Ultrasensitive second-harmonic generation frequency-resolved optical gating by aperiodically poled LiNbO3 waveguides at 1.5 microm

We retrieve intensity and phase profiles of 280 fs, 50 MHz optical pulses with 124 aJ coupled pulse energy (960 photons) by second-harmonic generation (SHG) frequency-resolved optical gating, using aperiodically poled LiNbO3 waveguides. The strong nonlinear interaction that is due to confinement within the micrometer-sized waveguide structure and the linearly chirped poling period contribute, respectively, to high SHG efficiency and broad phase-matching bandwidth. The achieved sensitivity is 2.7 x 10(-6) mW2, improving on the previous record for self-referenced complete pulse characterization by 5 orders of magnitude.

Highly sensitive differential tomographic technique for real-time ultrashort pulse characterization

We demonstrate a highly sensitive real-time optical pulse characterization technique based on differential chronocyclic tomography. The spectral intensity and phase of the pulse under test are reconstructed analytically from two experimental traces measured simultaneously in the spectral domain. The high sensitivity and accuracy are made possible by lock-in detection of the differential spectra in the simplified chronocyclic tomography. An accuracy of approximately 0.04 rad of spectral phase recovery is achieved with a 10-Hz refresh rate and 10-microW sensitivity. We also show that the measurement technique is applicable to pulses as short as approximately 100 fs.

Cross-correlation frequency-resolved optical gating coherent anti-Stokes Raman scattering with frequency-converting photonic-crystal fibers

Photonic-crystal fibers provide a high efficiency of frequency upconversion of regeneratively amplified femtosecond pulses of a Cr: forsterite laser, permitting the generation of subpicosecond anti-Stokes pulses with a smooth temporal envelope and a linear positive chirp, ideally suited for femtosecond coherent nonlinear spectroscopy. These pulses from a photonic-crystal fiber were cross correlated in our experiments with the femtosecond second-harmonic output of the Cr: forsterite laser in toluene solution, used as a test object, in boxcars geometry to measure the spectra of coherent anti-Stokes Raman scattering (CARS) of toluene molecules (XFROG CARS).