Volumetric intensity dependence on the formation of molecular and atomic ions within a high intensity laser focus

Abstract

The mechanism of atomic and molecular ionization in intense, ultra-short laser fields is a subject which continues to receive considerable attention. An inherent difficulty with techniques involving the tight focus of a laser beam is the continuous distribution of intensities contained within the focus, which can vary over several orders of magnitude. The present study adopts time of flight mass spectrometry coupled with a high intensity (8 x 10(15) Wcm(-2)), ultra-short (20 fs) pulse laser in order to investigate the ionization and dissociation of the aromatic molecule benzene-d1 (C(6)H(5)D) as a function of intensity within a focused laser beam, by scanning the laser focus in the direction of propagation, while detecting ions produced only in a "thin" slice (400 and 800 microm) of the focus. The resultant TOF mass spectra varies significantly, highlighting the dependence on the range of specific intensities accessed and their volumetric weightings on the ionization/dissociation pathways accessed.

Z-scan method for nonlinear saturation intensity determination, using focused intense laser beams

“…For example, early quenching of the less efficient process can result in its effective I sat attenuation. Similarly, product depletion by sequential processes [30,36,38] with similar saturation may shift I sat of the initial product to lower values due to the rise of a secondary process. In this paper we demonstrate the Z-scan method measuring saturation intensities spanning two orders of magnitude for SF 6 − nonlinear single and nonsequential [17] multiple photodetachment processes.…”

“…Another efficient method for peak intensity variation is by displacement of a focusing element and moving the focal plane away from the target, a scheme often used in many cross-beam experiments and referred to as a "Z-scan" [11,33,[35][36][37][38][39][40]. Z-scan measurements were previously analyzed to extract threshold intensities based by comparison to numerical simulations [37], assuming all atoms exposed to intensities above a certain threshold are ionized.…”

Highly Reliable Dynamic Random Access Memory Technology for Application Specific Memory with Dual Nitrogen Concentration Gate Oxynitrides Using Selective Nitrogen Implantation

“…(2) Initially, multiphoton ionization is more important, with field ionization and fieldassisted dissociation growing in importance as the power densities increase [68][69][70][71]. At least to 10 12 -10 13 W cm −2our typical range of operation-there tends to be relatively little ionic fragmentation even for polyatomics, although there is the possibility of more fragmentation with larger molecules [69,72,73]. (3) Fragmentation is minimized if the wavelength of the fs excitation is well out of the chromophore absorbance region [70,[74][75][76][77].…”

Resolving Strong Field Dynamics in Cation States of CO_2 via Optimised Molecular Alignment

“…The resulting focal volume averaging is strongest in the propagation direction of the laser beam, which offers a convenient way to limiting this source of uncertainty in laser intensity. Due to the spatial separation of different intensity regions within the focus, one may insert a narrow slit in front of the TOF drift region and thereby limit the detection to a certain intensity slice of the focus [168,169]. This also offers a way of varying the effective intensity by translating the focus along its propagation direction in front of the slit.…”

“…Assuming a Gaussian beam profile perpendicular to the propagation direction and a Lorentzian profile along this direction, the intensity distribution is given as [169]:…”