Parametric transformation and spectral shaping of supercontinuum by high-intensity femtosecond laser pulses (original) (raw)

Characteristics of femtosecond laser pulses propagating in multiply ionized rare gases

Nuclear Instruments and Methods in Physics Research Section B: Beam Interactions with Materials and Atoms, 2017

A three-dimensional non-adiabatic model in combination with a rate equation model is used to characterize high-intensity (>10 16 W/cm 2) femtosecond laser pulse propagation in atomic gas medium. In these conditions the atoms in the target gas will become multiply charged ions, while the laser pulse will propagate in a medium with high electron concentration created by itself. We obtain pulse characteristics in time, frequency and space domain for two representative cases: 800 nm and 267 nm (third harmonic) multicycle pulses which are both of practical importance. We show that the spatial-temporal variation of the refractive index in the macroscopic medium is the primary reason for pulse temporal/spectral and spatial shaping during propagation.

Supercontinuum generation of ultrashort laser pulses in air at different central wavelengths

2007

Supercontinuum generation by femtosecond filaments in air is investigated for different laser wavelengths ranging from ultraviolet to infrared. Particular attention is paid on the role of third-harmonic generation and temporal steepening effects, which enlarge the blue part of the spectrum. A unidirectional pulse propagation model and nonlinear evolution equations are numerically integrated and their results are compared. Apart from the choice of the central wavelength, we emphasize the importance of the clamped intensity reached by self-guided pulses, together with their temporal duration and propagation length as key players acting on both supercontinuum generation of the pump wave and emergence of the third harmonic. Maximal broadening is observed for large wavelengths and long filamentation ranges. Ó 2007 Published by Elsevier B.V.

Self-Trapping of Supercontinuum Generated by Femtosecond Pulses in a Noble Gas

International Conference on Ultrafast Phenomena, 2010

The observation of ultra-broadband supercontinuum generation in gases was first reported by Corkum et al. . The possibility to produce high energy white-light continua (WLC) using ultra-short pulses has sparked interest in applications such as remote sensing in the atmosphere [2] and nonlinear spectroscopy . In contrast to white-light generation in solid-state fibers, the nature of WLC generation in gases is not fully understood. The opportunity of having a broadband source of radiation confined in one beam with high spectral energy density has paved the way for replacing conventional sources of radiation such as optical parametric generators/amplifiers (OPGs/OPAs) . The use of parametric devices requires phase matching of nonlinear crystals to generate and amplify certain frequencies which lead to the repeated realignment of optical experiments. In addition, the importance of having good spatial quality beams for nonlinear optical experiments often requires spatial filtering. The spatial properties of WLC from gases have been shown to be excellent over most of their bandwidth. Thus, having a single white-light filament as a tunable source requires only the use of narrow band-pass filters in order to perform nonlinear spectroscopic characterization of materials . Based on this, there is an ongoing effort to understand the mechanisms and limitations involved in producing a high energy ultra-broadband source of radiation.

Super-Continuum femtosecond Laser generation

2020

A novel methodology to produce a high-power femtosecond using supercontinuum generation in hollowfiber has been developed. In this work, femtosecond high energy laser pulses have been observed. These pulses were generated due to supercontinuum caused by self –phase modification (SPM) in neon gas filled in a one-meter hollowfiber followed by two chirped-mirrors for dispersion compensation. The created pulses reached high energy of submJ at 1 KHz repetition rate. The characterization of femtosecond pulses in the regime of few-cycle pulses is considered using spectral phase interferometry for direct electric-field reconstruction (SPIDER). The SPIDER was used to observe precise measurements of pulse duration. The spectral bandwidth found to reach ultra-wide range from 600 – 950 nm. It has been found that the output pulse width is affected by the pulse duration of the injected femtosecond pulses into the optical fiber under different gas pressures. The observed results revealed that the ...

Supercontinuum Emission from Focused Femtosecond Laser Pulses in Air

AIP Conference …, 2011

We present our experimental results from the measurements of Supercontinuum emission (SCE) from air resulting from propagation of tightly focused femtosecond (40 fs) laser pulses. The effect of linearly polarized (LP) and circularly polarized (CP) light pulses on the SCE in two different external focal geometries (f/6, f/15) is presented. A considerable shift in the minimum wavelength of SCE is observed with external tighter focusing.

Supercontinuum emission from tightly focused femtosecond pulses in air: beyond intensity clamping

Proceedings of SPIE, 2010

We present the evolution of supercontinuum emission (SCE) from tightly focused fs laser pulses propagating in air. 45 fs laser pulses at 806 nm, 10 Hz repetition rate, from Ti:Sapphire laser (Thales Laser, Alpha 10) with a nanosecond contrast ratio better than 10 −6 : 1 are focused in air by a lens to an f/12 focusing geometry in one case, and by an off-axis parabolic mirror leading to an f/6 focusing in another. The laser input power is varied in the range of 10 -90 P Cr and 6 -60 P Cr in the f/12 and f/6 focusing geometries, respectively, where the critical power for selffocusing in air is P Cr = 3 GW for 806 nm. The effect of the tight focusing condition on the SCE spectrum and the dependence on the input laser polarization are studied. Within the input power range used in the study, the blue edge (the maximum positive frequency shift) of the SCE spectrum is found to decrease continuously when the laser energy is increased. This result is in contrast with previous measurements of SCE in condensed matter and gases with loose focusing geometry, for which a constant blue edge was interpreted as due to intensity clamping. We propose a model, which show that for tight focusing conditions, external focusing prevails over the optical Kerr effect annihilating plasma defocusing and self-focusing, thereby giving access to a new propagation regime featured by an efficient laser energy deposition in fully ionized air and intense 10 15 W/cm 2 pulses at the focus.

Atom driven by superstrong laser fields as a source of ultrashort-pulse XUV radiation

1996

Recent progress in the technique of generation and amplification of ultrashort laser pulses has resulted in the production of pulse duration of the order of or even shorter than 10 fs [1,2]. The use of Ti:Sa active crystals and broad-band optical elements, perfect compensation of wave dispersion in laser cavities and thorough comprehension of mode locking at self-focusing nonlinearity (Kerr-lens-mode-locking) have provided pulses having only few (∼3) optical cycles. Application of such a remarkable instrument opens up new prospects for experimental research on the interaction of ultrashort pulses with matter. It is also evident that a time has come for a serious theoretical analysis of these interaction models. Our report addresses the problem on nonlinear spectrum conversion of high intensity ultrashort laser pulses during the process of rapid optically-induced gas ionization.