Phase-modulated Laser Pulses Research Articles

Numerical modeling of optical coherent transient processes with complex configurations—II. Angled beams with arbitrary phase modulations

This work is a continuation of the development of the theoretical model for optical coherent transient (OCT) processes with complex configurations. A theoretical model for angled beams with arbitrary phase modulation has been developed based on the model presented in our previous work for the angled beam geometry. A numerical tool has been devised to simulate the OCT processes involving angled beams with the frequency detuning, chirped, and phase-modulated laser pulses. The simulations for pulse shaping and arbitrary waveform generation (AWG) using OCT processes have been performed. The theoretical analysis of programming and probe schemes for pulse shaper and AWG is also presented including the discussions on the rephasing condition and the phase compensation. The results from the analysis, the simulation, and the experiment show very good agreement.

Features of nonstationary SHG of phase-modulated laser pulses under self-action conditions

The influence of self-action effects on the efficiency of SHG of phase-modulated laser pulses in a nonstationary regime is analysed using a generalised method of strong interaction of nonlinear waves. An analytic solution for the SHG efficiency is obtained taking into account the depletion of pump radiation, the influences of the linear phase mismatch, mismatch of group velocities, and higher linearities. It is shown that the effects of self-action, mismatch of group velocities, and linear phase mismatch can compensate for each other, resulting in an increase in the efficiency of SHG of phase-modulated pulses.

Multiphoton Intrapulse Interference. 1. Control of Multiphoton Processes in Condensed Phases

We explore and demonstrate the use of phase-modulated ultrafast laser pulses for controlling nonlinear optical processes in large molecules, proteins, and solid materials. Our experiments illustrate that in condensed phases, when spectra are broad, the spectrum of the nth-order electric field, determined by multiphoton intrapulse interference, plays a major role in controlling multiphoton excitation. These findings determine key parameters (amplitude, period, and symmetry of the phase function) for coherent femtosecond laser control in condensed phases.

Programmable amplitude- and phase-modulated femtosecond laser pulses in the mid-infrared

We present a scheme to produce programmable phase- and amplitude-modulated femtosecond laser pulses in the mid-infrared regime of 3-10mum by difference frequency mixing. The 80-fs signal output of an optical parametric amplifier is shaped with a liquid-crystal mask and mixed in an AgGaS(2) crystal with a temporally stretched idler pulse. Without changing the mechanical alignment, we produce programmable amplitude modulations and chirped pulses at lambda=3mum with energy as high has thas 1muJ . This scheme, further, allows the generation of controllable pulse sequences. The results are in good agreement with theoretical simulations.

Femtosecond pump–probe photoelectron spectroscopy on Na2: a tool to study basic coherent control schemes

Femtosecond pump–probe photoelectron spectroscopy has become a common tool in ultrafast gas-phase science because of its sensitivity both to structural and electronic changes in a molecule upon excitation. Here a summary and extended discussion of our experiments is presented. We focus on the potential of this method to study basic femtosecond coherent control schemes. Multi-photon excitation of the Na2 molecule with femtosecond laser pulses leads to preparation of vibrational wave packets. Mapping of the vibrational wave-packet dynamics by time-resolved photoelectron spectroscopy offers the high spatial and temporal resolution required to investigate a variety of laser-control parameters in great detail. Besides an illustration of the Tannor–Kosloff–Rice scheme we demonstrate electronic transitions at Franck–Condon forbidden internuclear distances due to the intensity of the applied laser pulses. Further we discuss the influence of simple phase-modulated (linearly chirped) laser pulses on a molecular multi-photon process. An enhanced population transfer is derived due to synchronization of the wave-packet motion on an electronic potential to an appropriate chirp of the laser pulses. In addition, the influence of the temporal profile on the population transfer and the role of the pulse duration are studied.

Chronocyclic description of laser pulse compression

The compression of phase modulated laser pulses with a grating compressor is analysed with the aid of the Wigner distribution function. The time-frequency display of the compressed pulses gives clear indication of the optimum compressor parameters, which would lead to a routine for the optimisation of time-requency devices such as compressors, stretchers and pulse shapers. The description of the compressor in terms of the Wigner function overcomes the problem of the missing information about instant frequencies of the Fourier transform, allowing for a more complete characterisation of those devices.

Control of atomic transitions by the symmetry of excitation pulses

It is shown that any N-level atom or molecule coherently driven by laser pulses, whose Rabi frequencies and detunings are arbitrary odd functions of time, is restored completely to its initial state after the pulses have been turned off. Interaction of atoms or molecules with amplitude and phase modulated laser pulses provides a physical example in which this effect can be observed.

Amplification of ultrashort phase-modulated laser pulses in media with a discrete spectrum

A theory of the amplification of phase-modulated ultrashort laser pulses is developed for media having a discrete and approximately equidistant gain band structure. It is shown that fundamentally new propagation regimes are feasible in this case. Depending on the parameters of an input pulse, trains of ultrashort pulses of fixed period or having a period governed by the phase modulation of the input pulse may be formed as a result of the amplification. A general method is proposed for the study of the propagation of phase-modulated pulses in media having an arbitrary gain band structure. It is also shown that phase modulation of an input pulse may increase appreciably the energy of the amplified pulses.

Propagation of phase-modulated coherent radiation pulses in resonant media

A theoretical analysis is made of the propagation of phase-modulated laser pulses in a resonant two-level medium. It is shown that phase modulation results in the appearance of qualitatively new amplification (absorption) regimes. In one of these regimes, trains of ultrashort pulses may be generated at a high repetition frequency. An analysis is also made of the feasibility of compression of amplified pulses.

Preparation of constant-bandwidth total inversion, independent of optical density, with phase-modulated laser pulses.

Preparation of constant-bandwidth total inversion, independent of optical density, with phase-modulated laser pulses.

Implementation of a phase and amplitude modulated π pulse for coherent optical spectroscopy

We have implemented an amplitude and phase modulated laser pulse of the form [sech(αt)]1+3i. Such a pulse shape creates uniform population inversion within a selected bandwidth, compensates for Rabi frequency inhomogeneity, and leaves transitions outside the bandwidth unaffected. The unique features of this pulse shape are verified by measuring total fluorescence in iodine vapor as a function of laser power.

Nonsteady genration of total frequency with phase-modulated supershort laser pulse

Nonsteady genration of total frequency with phase-modulated supershort laser pulse