Space-frequency coupling, conical waves, and small-scale filamentation in water

Numerical simulations of fs laser propagation in water have been made to explain the small-scale filaments in water we have observed by a nonlinear fluorescence technique. Some analytical descriptions combined with numerical simulations show that a space-frequency coupling mainly from the interplay among self-phase modulation, dispersion and phase mismatching will reshape the laser beam into a conical wave which plays a major role of energy redistribution and can prevent laser beam from self-guiding over a long distance. An effective group velocity dispersion is introduced to explain the pulse broadening and compression in the filamentation. (c) 2005 American Institute of Physics.

Few-cycle spatiotemporal soliton wave excited by filamentation of a femtosecond laser pulse in materials with anomalous dispersion

The nonlinear dynamics of 1.6-mu m fs laser pulses propagating in fused silica is investigated by employing a full-order dispersion model. Different from the x-wave generation in normally dispersive media, a few-cycle spatiotemporally compressed soliton wave is generated with the contrary contributions of anomalous group velocity dispersion (GVD) and self-phase-modulation. However, at the tailing edge of the pulse forms a shock wave which generates separate and strong supercontinuum peaked at 670 nm. It is also the origin of conical emission formed both in time and frequency domain with the contribution of normal GVD at visible light.

Ultrafast control of multiple filamentation by ultrafast laser pulses

Control of multiple filamentation by laser-induced microlens effect due to a nonlinear interaction of two overlapping laser beams inside a glass plate was demonstrated. Individual or multiple spots on the white light pattern which is a product of multiple filamentation through a mesh can be switched on and off with a very high contrast ratio on a femtosecond time scale. This phenomenon can find applications such as ultrafast optical switch and high-speed sampling. (C) 2005 American Institute of Physics.

Temperature controlled filamentation in argon gas

Temperature controlled filamentation is experimentally demonstrated in a temperature gradient gas-filled tube. The proper position of the tube is heated by a furnace and two ends of the tube are cooled by air. The experimental results show that multiple filaments are shrunken into a single filament or no filament only by increasing the temperature at the beginning of the filament. This technique offers another degree of freedom of controlling the filamentation and opens a new way for intense monocycle pulse generation through gradient temperature in a noble gas.

Polarization-dependent pulse compression in an argon-filled cell through filamentation

Pulse compression through filamentation in an argon-filled cell was experimentally demonstrated by using circularly and linearly polarized pulses. A 53 fs circularly polarized pulse was successfully compressed to 15 fs. By using circularly polarized pulse input, the broadened spectrum was much wider and the incident energy in the gas cell can be increased by more than 3/2 times. Much shorter pulse could be compressed by using circularly polarized pulse input. [GRAPHICS] The temporal profile of the compressed pulse (C) 2008 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA.

Formation of X-waves at fundamental and harmonics by infrared femtosecond pulse filamentation in air

We experimentally observe the formation of X-waves at fundamental, third harmonic, and fifth harmonic wavelengths by infrared (central wavelength at similar to 1500 nm) femtosecond laser pulse filamentation in air. By fitting the angularly resolved spectra of the fundamental and harmonic waves using X-wave relations, we confirm that all the X-waves have nearly the same group velocity, indicating that they are locked in space and time during their propagation in filament.

Spectral analysis and control to obtain sub-5 fs pulses by femtosecond filamentation

A spectral-filter method is numerically demonstrated to obtain sub-5 fs pulses by using femtosecond filamentation in fused silica. Instead of employing spectral phase compensation, by properly employing a high-pass filter to select the broadened high-frequency spectra that are located almost in phase in the tailing edge of the self-compressed pulses owing to self-steepening, as short as single-cycle pulses can be obtained. For instance, for an input pulse with a duration of 50 fs and energy 2.2 mu J, the minimum pulse duration can reach to similar to 4 fs (about 1.5 cycles) by applying a proper spectral filter. (C) 2008 Optical Society of America

Spectral evolution of angularly resolved third-order harmonic generation by infrared femtosecond laser-pulse filamentation in air

We experimentally investigate the evolution of an angularly resolved spectrum of third harmonic generated by infrared femtosecond laser pulse filamentation in air. We show that at low pump intensity, phase matching between the fundamental and third-harmonic waves dominates the nonlinear optical effect and induces a ring structure of the third-harmonic beam, whereas at high pump intensity, the dispersion properties of air begin to affect the angular spectrum, leading to the formation of a nonlinear X wave at third harmonic.

X-shaped third harmonic generated by ultrashort infrared pulse filamentation in air

The authors report the measurement of the angularly resolved spectrum of the third harmonic generated in a femtosecond filament in air and its evolution with increasing pump power. Pumped by a focused infrared ultrashort pulse with a carrier wavelength of 1270 nm, a pulse duration of similar to 20 fs, and pulse energy up to 487 mu J, the generated third harmonic is composed of an on-axis emission and a conical ring emission. When the pump power is sufficiently high, angularly resolved spectra with significant X-like feature could be observed, indicating the formation of nonlinear X wave at third harmonic. (c) 2008 American Institute of Physics.

Generation of sub-5 fs pulses through cascade of filamentation and hollow fiber compression

A pulse-compression scheme based on cascade of filamentation and hollow fiber has been demonstrated, Pulses with duration of sub-5 fs and energy of 0.2 mJ near 800 nm have been generated by compressing the similar to 40 fs pulses from a commercial laser system. This method is promising to generate near monocycle high energy pulses. [GRAPHICS] Measured autocorrelation curve of the final compressed pulses with duration of sub-5 fs (black solid) and the simulated autocorrelation curve of 4.6 fs pulse near 800 rim (red dash) (C) 2008 by Astro Ltd. Published exclusively by WILEY-VCH Verlag GmbH & Co. KGaA

Filamentation control in the temperature gradient argon gas

A novel technique of controlling the evolution of the filamentation was experimentally demonstrated in an argon gas-filled tube. The entrance of the filament was heated by a furnace and the other end was cooled with air, which resulted in the temperature gradient distribution along the tube. The experimental results show that multiple filaments are merged into a single filament and then no filament by only increasing the temperature at the entrance of the filament. Also, the filament can appear and disappear after increasing the local temperature and input pulse energy in turn. This technique offers another degree of freedom to control the filamentation and opens a new way for multi-mJ level monocycle pulse generation through filamentation in the noble gas.

Pulse compression by filamentation in argon with an acoustic optical programmable dispersive filter for predispersion compensation

We have experimentally demonstrated pulses 0.4 mJ in duration smaller than 12 fs; with an excellent spatial beam profile by self-guided propagation in argon. The original 52 fs pulses from the chirped pulsed amplification laser system are first precompressed to 32 fs by inserting an acoustic optical programmable dispersive filter instrument into the laser system for spectrum reshaping and dispersion compensation, and the pulse spectrum is subsequently broadened by filamentation in an argon cell. By using chirped mirrors for post-dispersion compensation, the pulses are successfully compressed to smaller than 12 fs.

Compression of intense laser pulse through filamentation in an argon-filled cell

We demonstrate a pulse compression technique through filamentation in an argon-filled cell. By using a pair of chirped mirrors for dispersion compensation, we have successfully compressed the 53 fs pulse to 15 fs with good spatial qualities and good pulse stability. The total transmitted efficiency is more than 75%. The influence of the experiment parameters to the compressed pulses is also studied experimentally.

Control of filamentation induced by femtosecond laser pulses propagating in air

Filamentation formed by self-focusing of intense laser pulses propagating in air is investigated. It is found that the position of filamentation can be controlled continuously by changing the laser power and divergence angle of the laser beam. An analytical model for the process is given.

Femtosecond filamentation and supercontinuum generation in silver-nanoparticle-doped water

The authors report the investigation of filament and supercontinuum generation by focusing a femtosecond laser beam into water doped with silver nanoparticles. The silver nanoparticles enhance the nonlinear optical response of water, leading to broadening of supercontinuum spectra in self-focused femtosecond filaments. During the propagation of the supercontinuum light in the filament, the silver nanoparticles preferentially scatter the short-wavelength light near the plasmon resonant wavelength peak, followed by the scattering of the long-wavelength light. Thus, a side view of the filament shows a full-color spectrum in the visible range, which is herein called "rainbow filament." (c) 2007 American Institute of Physics.