Two-color Ultrashort Laser Pulses Research Articles

Remote terahertz spectroscopy from extended two-color plasma filaments: The ALTESSE 2 project

Coherent time-domain spectroscopy (TDS) using terahertz radiation is valuable for fundamental science, security, and medical applications. This study investigates the performance of air-biased coherent detection terahertz spectroscopy (ABCD-THz) when an extended plasma filament is created in the air over long distances. We report on the latest results obtained within the follow-up of the ALTESSE project (Bergé L. et al., EPL, 126 (2019) 24001) whose objective is to measure a set of spectral signatures characterizing suspicious materials over meter-long distances. As one of the most critical steps towards routinely applying this technique, we verified the feasibility of a remote THz time-domain spectroscopy by loosely focusing two-color ultrashort laser pulses at more than 3 meters from the laser source. The absorption spectra of amino acids and explosives analyzed in such a filamentation geometry are compared with those obtained using a standard ABCD scheme where the plasma is generated at much shorter distances of .

Characterization of two-color ultrashort laser pulses using polarization-gating and transient-grating frequency-resolved optical gating

Two-color ultrashort laser pulses have emerging applications in numerous areas of science and technology. In many cases, the slightest change in the combined electric field of a two-color pulse greatly affects its interaction mechanism with the system. Therefore, a precise characterization of the temporal/spectral profile of the combined electric field is of great importance. In this work, we demonstrate that a full characterization is possible using the well-known transient-grating (TG) or polarization-gating (PG) frequency-resolved optical gating (FROG) techniques, and by employing the recently developed Retrieved-Amplitude N-grid Algorithmic (RANA) approach for the retrieval process. We demonstrate the validity of using these techniques and this approach for multi-cycle and few-cycle pulses in the absence and presence of noise.

Study of terahertz generation via the interaction of two-color ultra-short laser pulses with water vapor plasmas

In this work, using a two dimensional particle in cell-Monte Carlo collision simulation scheme, the Terahertz (THz) generation process via the interaction of a two-color ultra-short laser pulses with the water vapor gas (H2O) is examined. The background gas pressure and various laser parameters, e.g., its pulse shape, duration, and waist, are varied, and their effects on the temporal variation of the generated current density, THz electric field, and THz spectral intensity are studied. It is shown that the best pulse shape generating the THz signal radiation with the highest intensity is a trapezoidal pulse. Moreover, the intensity of generated THz radiation is increased at the higher pulse durations and waists. In addition, at the higher water vapor gas pressures, the time to peak of the generated current density is shifted to the earlier moments. Finally, it is observed that, for the laser pulses with the intensities of about 8 × 1013 W/cm2, the water vapor triatomic molecules are a proper source for the THz radiation generation under the illumination of high power ultra-short two-color laser pulses.

Kinetic study of terahertz generation based on the interaction of two-color ultra-short laser pulses with molecular hydrogen gas

In this work, using a two dimensional particle in cell-Monte Carlo collision simulation scheme, interaction of two-color ultra-short laser pulses with the molecular hydrogen gas (H2) is examined. The operational laser parameters, i.e., its pulse shape, duration, and waist, are changed and, their effects on the density and kinetic energy of generated electrons, THz electric field, intensity, and spectrum are studied. It is seen that the best pulse shape generating the THz signal radiation with the highest intensity is a trapezoidal pulse, and the intensity of generated THz radiation is increased at the higher pulse durations and waists. For all the operational laser parameters, the maximum value of emitted THz signal frequency always remains lower than 5 THz. The intensity of applied laser pulses is taken about 1014 w/cm2, and it is observed that while a small portion of the gaseous media gets ionized, the radiated THz signal is significant.

Directional bond breaking by polarization-gated two-color ultrashort laser pulses

We experimentally investigate directional bond breaking in dissociative single ionization of H2 driven by circularly polarized two-color ultrashort pulses of counter- and co-rotating laser fields. Trefoil or semilunar patterns of directional proton emission in a two-dimensional space spanned by the laser fields are observed, which can be finely controlled by varying the relative phase of the counter- or co-rotating circularly polarized two-color fields, respectively. Our results open new possibilities to manipulate two-dimensional directional bond breaking of molecules by strong laser fields.

Parametric study of broadband terahertz radiation generation based on interaction of two-color ultra-short laser pulses

In this work, using a two-dimensional kinetic model based on particle in cell-Monte Carlo collision simulation method, the influence of different parameters on the broadband intense Terahertz (THz) radiation generation via application of two-color laser fields, i.e., the fundamental and second harmonic modes, is studied. These two modes are focused into the molecular oxygen (O2) with uniform density background gaseous media and the plasma channels are created. Thus, a broadband THz pulse that is around the plasma frequency is emitted from the formed plasma channel and co-propagates with the laser pulse. For different laser pulse shapes, the THz electric field and its spectrum are both calculated. The effects of laser pulse and medium parameters, i.e., positive and negative chirp pulse, number of laser cycles in the pulse, laser pulse shape, background gas pressure, and exerted DC electric field on THz spectrum are verified. Application of a negatively chirped femtosecond (40 fs) laser pulse results in four times enhancement of the THz pulse energy (2 times in THz electric field). The emission of THz radiation is mostly observed in the forward direction.

Modulation on Optical Limiting and Two-Photon Absorption Behavior of a Molecular Medium by Two-Color Ultrashort Laser Pulses

The dynamical behavior of two-color ultrashort laser pulse propagating in a molecular medium 4,4'-bis(di-n -butylamino)stilbene (BDBAS) has been studied by employing an iterative predictor-corrector finite-difference time domain (FDTD) tech- nique to solve the Maxwell-Bloch equations. The results indicate that the spectrum of electric field shows oscillation feature around the two-photon resonant frequency when the delay time exists due to the interaction between two sub-pulses. The opti- cal limiting window turns narrower and the saturation value of output intensity gets larger with the presence of delay time compared with no delay time case. The dynam- ical TPA cross section is smaller with the increase of delay time. The studies suggest a method to modulate the nonlinear optical properties of the medium by controlling the delay time of the two-color pulse. PACS: 33.80.-b, 82.50.Pt, 31.15.A-

Broadband coherent light generation in a Raman-active crystal driven by two-color femtosecond laser pulses

We demonstrate broadband light generation by focusing two-color ultrashort laser pulses into a Raman-active crystal, lead tungstate (PbWO(4)). As many as 20 anti-Stokes and 2 Stokes fields are generated due to strong near-resonant excitation of a Raman transition. The generated spectrum extends from the infrared, through the visible region, to the ultraviolet, and it consists of discrete spatially separated sidebands. Our measurements confirm good mutual spatial and temporal coherence among the generated fields and open possibilities for synthesis of subfemtosecond light waveforms.

Absolute phase control of spectra effects in a two-level medium driven by two-color ultrashort laser pulses

Using a ω – 3 ω combination scenario, we investigate the absolute phase control of the spectra effects for ultrashort laser pulses propagating in a two-level medium. It is found that the higher spectral components can be controlled by the absolute phases. In particular, different absolute phase combinations can lead to the buildup or split of the even harmonics.

Formation of higher spectral components in a two-level medium driven by two-color ultrashort laser pulses

Using a $\ensuremath{\omega}\ensuremath{-}2\ensuremath{\omega}$ combination scenario, we investigate the spectra of two-color ultrashort laser pulses in a two-level medium. It is found that higher spectral components can be produced even for small area pulses due to the interference effect of the two laser pulses. Moreover, these higher spectral components depend crucially on the relative phase $\ensuremath{\varphi}$ of the two laser pulses: continuum and distinct peaks can be achieved through the control of the relative phase.