Abstract
We report on some interesting phenomena in the focusing and scattering of femtosecond laser pulses in free space that provide insights on intense laser plasma interactions. The scattered image in the far field is analyzed and the connection with the observed structure of the plasma at the focus is discussed. We explain the physical mechanisms behind the changes in the colorful and intricate image formed by scattering from the plasma for different compressions, as well as orientations of plano-convex lens. The laser power does not show significant effect on the images. The pulse repetition rate above 500 Hz can affect the image through slow dynamics The spectrum of each color in the image shows oscillatory peaks due to interference of delayed pulse that correlate with the plasma length. Spectral lines of atomic species are identified and new peaks are observed through the white light emitted by the plasma spot. We find that an Ar gas jet can brighten the white light of the plasma spot and produce high resolution spectral peaks. The intricate image is found to be extremely sensitive and this is useful for applications in sensing microscale objects.
Highlights
Femtosecond laser pulses amplified through chirp pulse amplification (CPA) technique in Ti:Sa system has sufficient power and intensity to ionize atomic and molecular gases through multiphoton and tunnelling ionization processes, despite its fixed central wavelength λ = 800 nm at near infrared region
Similar results were reported on the breakup of the pulse into two conical sections by slightly tilting the lens with the corresponding spectra that depend on the position of the pulses diffracted by the focused spot[5]
The self-focusing ultrafast Ti: Sapphire laser pulses in air and gas can produce plasma column composed of highly excited ions, providing useful photoemission spectra of atomic and molecular species[6]
Summary
Femtosecond Laser Pulses received: 24 June 2015 accepted: 02 August 2016 Published: 30 August 2016. Spectral lines of atomic species are identified and new peaks are observed through the white light emitted by the plasma spot. The self-focusing ultrafast Ti: Sapphire laser pulses in air and gas can produce plasma column composed of highly excited ions, providing useful photoemission spectra of atomic and molecular species[6]. We study the spectra of white light generated from a focused femtosecond laser pulses into air. The underlying mechanism of a single pulse may be different from laser induced breakdown spectroscopy (LIBS)[8] but perhaps not the train of pulses with 1 kHz. The laser-plasma interaction process provides a potentially important spectroscopic method where a plasma column is created at the focal spot in a gas by direct photoionization, producing spectra with smaller line broadening and a low level of continuum. By passing through an Ar gas jet, we study the changes in the spectral peaks and the presence of new compounds interacting with Argon gas
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