Gennady Rasskazov

Spectral amplitude and phase noise characterization of titanium-sapphire lasers

There are few methods capable of characterizing pulse-to-pulse noise in high repetition rate ultrafast lasers. Here we use a recently developed method, termed fidelity, to determine the spectral amplitude and phase noise that leads to lack of pulse repeatability and degrades the performance of laser sources. We present results for a titanium sapphire oscillator and a regenerative amplifier system under different noise conditions. Our experimental results are backed by numerical calculations.

Quantifying noise in ultrafast laser sources and its effect on nonlinear applications

Nonlinear optical applications depend on pulse duration and coherence of the laser pulses. Characterization of high-repetition rate pulsed laser sources can be complicated by their pulse-to-pulse instabilities. Here, we introduce and demonstrate experimentally a quantitative measurement that can be used to determine the pulse-to-pulse fidelity of ultrafast laser sources. Numerical simulations and experiments illustrate the effect of spectral phase and amplitude noise on second and third harmonic generation.

Anomalous laser-induced group velocity dispersion in fused silica

We present 20fs(2) accuracy laser-induced group velocity dispersion (LI-GVD) measurements, resulting from propagation of a femtosecond laser pulse in 1mm of fused silica, as a function of peak intensity. For a 5.5 × 10(11) W/cm(2) peak intensity, LI-GVD values are found to vary from -3 to + 15 times the material GVD. Normal induced dispersion can be explained by the Kerr effect, but anomalous LI-GVD, found when the input pulses have negative pre-chirp, cannot. These findings have significant implications regarding self-compression and the design of femtosecond lasers.

Phase-only synthesis of ultrafast stretched square pulses.

We report the generation of square temporal-shape pulses with no loss of spectral bandwidth, using an analytic expression for the spectral phase modulation dependent only on the input spectrum and stretching factor. We demonstrate numerically and experimentally conversion of 40fs pulses into 150 times longer flat top pulses with sharp on and off fronts. Applications in pulse amplification and free electron lasers are considered.

Real-time single-shot measurement and correction of pulse phase and amplitude for ultrafast lasers

Abstract. The transition of femtosecond lasers from the laboratory to commercial applications requires real-time automated pulse compression, ensuring optimum performance without assistance. Single-shot phase measurements together with closed-loop optimization based on real-time multiphoton intrapulse interference phase scan are demonstrated. On-the-fly correction of amplitude, as well as second- and third-order phase distortions based on the real-time measurements, is accomplished by a pulse shaper.

Eye-safe near-infrared trace explosives detection and imaging

We report the development of a non-contact no-reagents system operating in the eye-safe 1560-1800 nm wavelength range for standoff trace detection of explosives and high-speed imaging. Experimental results are provided for a number of chemicals including explosives on a variety of surfaces at sub-microgram per cm2 concentration. Chemically specific images were collected at 0.06 ms per pixel. Results from this effort indicate that the combination of modern industrial fiber lasers and nonlinear optical spectroscopy can address next generation eye-safe trace detection of chemicals including explosives.

Mitigating self-action processes with chirp or binary phase shaping

We report the use of binary phase shaping to mitigate pulse degradation and self-focusing in fused silica. The results of simulation and estimated mitigation efficiency are supported by experimental results using both chirped and binary phase-shaped pulses. Possible applications are considered.

Characterization and adaptive compression of a multi-soliton laser source.

Ultrashort pulse generation in the 1600 nm wavelength region is required for deep-tissue biomedical imaging. We report on the characterization and adaptive compression of a multi-soliton output spanning >300 nm from a large-mode area photonic-crystal fiber rod for two separate laser setups. Sub-30 fs pulses are generated by first compressing of each soliton individually, and then followed by coherently combining all of the pulses in the train, which are separated by hundreds of femtoseconds. Simulations of the source, together with amplitude and phase coherence measurements are provided.

Deviations from theory by femtosecond lasers due to noise

We compare deviations from theory in the yield of second harmonic generation in order to characterize high-repetition rate femtosecond laser sources where the amplitude and phase differs from pulse to pulse. Experimental results are presented for cases with phase noise and a post-pulse.

Binary phase shaping for mitigating self-phase modulation

In applications involving lasers with high peak intensities, such as optical amplification or pulse delivery through an optical fiber, self-phase modulation is an unwanted phenomenon which affects the spectrum, phase, and temporal profile of laser pulses. Here we report on the use of binary phase shaping for mitigation of self-phase modulation. We provide theoretical simulation and estimated efficiency of the mitigation supported by experimental results using both chirped and binary phase shaped pulses.