Weak Ultrashort Pulses Research Articles

Nonadiabatic optical transitions as a turn-on switch for pulse shaping

A strong nonresonant, asymmetric ultrashort pulse drives an atomic transition and causes a complete population inversion because of a sudden nonadiabatic jump. This jump is probed in real time by propagating a weak ultrashort pulse in the system which is resonant on an adjacent transition. The probe at the exit of the medium presents an oscillatory structure with the nonadiabatic jump marked in time by the onset of oscillations. The nonadiabatic jump thus acts as a ``turn-on'' switch for the shaping of the probe.

Beyond the pulse-area theorem: Role of the absorption and the dispersion in the propagation of weak ultrashort resonant pulses

We present here some fundamental but yet underlooked features of the propagation of weak ultrashort pulses (with Δ d τ << 1, where Δ d is the Doppler width and τ is the pulse duration) in resonant atomic media. We show that the pulse area behaviour and the pulse spectrum at resonance are governed by the usual optical depth ( α 0 L, where α 0 is the absorption coefficient at resonance and L the length of the medium), whereas the pertinent parameter that governs the severity of the dispersion effects and the distortion of the pulse is the dispersion parameter e disp = ( α 0 L) Δ d τ that we introduce. Paradoxical effect such as distortionless propagation (e.g. e disp << 1) with vanishing pulse area (when α 0 L >> 1) can then explained within this formalism.

Photon acceleration of ultrashort laser pulses by relativistic ionization fronts.

We present experimental results from the collision of weak ultrashort pulses with relativistic ionization fronts in copropagation and counterpropagation. The observed frequency upshifts of the probe pulses provide not only information about the electron density of the ionization front but also reveal the fine structure of the front. The connection between the correlation lengths for copropagation and counterpropagation and the longitudinal and transverse dimensions of the ionization front is also demonstrated thus showing the feasibility of using the frequency upshift experienced by short probe pulses to fully characterize relativistic ionization fronts and other relativistic coherent structures in laser-produced plasmas.

Amplitude and phase characterization of weak blue ultrashort pulses by downconversion

We present difference-frequency generation cross-correlation frequency-resolved optical gating, a new method of characterizing the amplitude and phase of weak ultrashort pulses in the blue spectral region. The method uses the spectrally resolved downconversion signal of the blue pulse and a fully characterized reference pulse with a lower center frequency. The amplitude and phase of the blue test pulse are retrieved from the corresponding spectrogram and electric field of the reference pulse with an interactive Fourier-transform algorithm.

Coherent effects in ultrashort pulse propagation through an optically thick three-level medium

A theoretical study is made of the propagation of a weak ultrashort pulse through an optically thick, inhomogeneously broadened three-level medium of the V configuration driven by a self-induced transparency pulse on the coupled transition. The weak coherent pulse experiences a greatly enhanced transparency. The new transparency effect is discussed in detail and the results are found to be in good agreement with recent experimental observations.

XFROG — A New Method for Amplitude and Phase Characterization of Weak Ultrashort Pulses

XFROG — A New Method for Amplitude and Phase Characterization of Weak Ultrashort Pulses

XFROG ? A New Method for Amplitude and Phase Characterization of Weak Ultrashort Pulses

We present a new method to characterize the amplitude and phase of weak ultrashort pulses. Our method is based on the spetrally resolved crosscorrelation signal of a weak test pulse with a fully characterized intensive reference pulse and requires no spectral overlap between the signal and the reference. To retrieve the amplitude and phase of the test pulse, we use an iterative Fourier transform algorithm with generalized projections.

Measurement of the intensity and phase of ultraweak, ultrashort laser pulses: erratum

We show that frequency-resolved optical gating combined with spectral interferometry yields an extremely sensitive and general method for temporal characterization of nearly arbitrarily weak ultrashort pulses even when the reference pulses is not transform limited. We experimentally demonstrate measurement of the full time-dependent intensity and phase of a train of pulses with an average energy of 42 zeptojoules (42 × 10−21 J), or less than one photon per pulse.

Measurement of the intensity and phase of ultraweak, ultrashort laser pulses

We show that frequency-resolved optical gating combined with spectral interferometry yields an extremely sensitive and general method for temporal characterization of nearly arbitrarily weak ultrashort pulses even when the reference pulses is not transform limited. We experimentally demonstrate measurement of the full time-dependent intensity and phase of a train of pulses with an average energy of 42 zeptojoules (42 x 10(-21) J), or less than one photon per pulse.