Anatoly Efimov

Programmable shaping of ultrabroad-bandwidth pulses from a Ti:sapphire laser

We have used a commercially available liquid-crystal spatial light modulator within a reflective optics pulse-shaping apparatus to shape ultrashort pulses with temporal resolution approaching 10 fs. Using the spatial light modulator as a phase modulator, we produce a variety of complex ultrafast waveforms, including odd pulses, high repetition rate (>23 THz) pulse trains, and asymmetric pulse trains. We also show that it is possible to compensate for large amounts of high-order phase dispersion (in excess of 60π) by appropriate cubic- and quartic-phase modulations of the pulse. Finally, we examine the limitations of shaping ultrabroad-bandwidth pulses. We find that, for specific classes of waveforms, Fourier-transform pulse-shaping techniques can be used for pulses with 5-fs durations, which exceed the current state of the art in ultrashort pulse generation. However, synthesis of general waveforms with 5-fs resolution will require compensating for nonlinear spatial dispersion of frequency in the masking plane.

Adaptive Control of Pulse Phase In A Chirped Pulse Amplifier

Using experimental feedback, we demonstrate that a chirped-pulse amplifier can adaptively learn to compensate for the higher-order phase dispersion that is inherent in the amplification process. A genetic algorithm-based search routine is used to repetitively update the pulse phase in a programmable pulse stretcher during a plasma breakdown experiment to maximize the magnitude of spectral blueshift. Reductions in pulse duration from 37 to 30 fs and substantially better wing structure are typically obtained as a result of the optimization.

Pulse shaping with the Gerchberg–Saxton algorithm

Generation of arbitrarily complex intensity profiles by using phase-only Fourier-domain pulse shaping has thus far been performed by using optimization algorithms to find the optimal phase profile. We present an alternative method based on the Gerchberg–Saxton (GS) algorithm that converges at least several hundred times faster and is independent of the number of phase points and gray levels. The numerical and experimental performance of the GS algorithm is characterized and compared against a genetic algorithm. An application of amplified GS-synthesized waveforms to large-amplitude coherent phonon generation and destruction is demonstrated.

Programmable dispersion compensation and pulse shaping in a 26-fs chirped-pulse amplifier

We have constructed a 26-fs chirped-pulse amplifier that incorporates a programmable liquid-crystal spatial light modulator in the pulse stretcher. The modulator serves a dual purpose. First, we apply frequency-dependent phase shifts to compensate for cubic, quartic, and nonlinear phase dispersion in the amplifier, which results in a reduction in pulse duration from 32 to 26 fs, in agreement with the transform limit of the amplified pulse spectrum. Second, we are able to produce high-fidelity compressed amplified shaped pulses by applying phase masks directly within the stretcher. Shaped pulse energies of greater than 1 mJ are routinely obtained.

Spectral adaptive optics: phase compensation for ultrashort chirped pulse amplifier systems

We propose a method for compensating phase dispersion in chirped pulse amplifier systems which is based on adaptive optics. By placing a feedback-controlled arbitrarily deformable mirror in the stretcher where frequency components are highly dispersed, arbitrarily high- order phase dispersion within the amplifier can be canceled by introducing the appropriate phase delay. To demonstrate this concept, we model a 10 fsec chirped pulse amplifier and show that transform limited pulses are obtainable. We also show that deleterious effects such as angular beam divergence and spatially dependent broadening are negligible. Finally, we discuss design considerations for a 1D adaptive optic mirror.

Adaptive control of lasers and their interactions with matter

Summary form only given. We present several results obtained in our laboratory on the use of adaptive feedback methods in controlling lasers and their interactions with matter. First, we describe a genetic algorithm-based feedback loop for optimizing laser pulses in a femtosecond pump-probe experiment. In particular, we study the effectiveness of feedback control under a variety of experimental conditions. We find that for simple control experiments, feedback can achieve the desired goal even in the presence of experimental noise. Second, we describe experiments in which feedback is used to control the motion of charge carriers in quantum wells. Finally, we describe experiments in which adaptive feedback is used to compensate phase dispersion in chirped pulse amplifiers by monitoring the ionization rate of molecules in a spectral blueshift experiment.

Shaping of ultrabroad bandwidth pulses: toward single-cycle control of optical fields

We demonstrate the shaping of ultrabroad bandwidth femtosecond optical pulses with temporal resolution approaching 10 fsec and explore the limitations of femtosecond ultrabroad bandwidth pulse shaping. Using a commercially available liquid crystal spatial light modulator within a reflective optics pulse shaping apparatus, we synthesize a variety of complex waveforms and show that it is possible to compensate for large amounts of high order phase dispersion by appropriate cubic and quartic phase modulation of the pulse. Finally, we theoretically examine inherent limitations of pulse shaping. Surprisingly, Fourier transform pulse shaping techniques are robust and can be used for pulses with 5 fsec durations, beyond the current capabilities of ultrafast laser systems.