Fragmentation of neutral amino acids and small peptides by intense, femtosecond laser pulses.

High power femtosecond laser pulses have unique properties that could lead to their application as ionization or activation sources in mass spectrometry. By concentrating many photons into pulse lengths approaching the timescales associated with atomic motion, very strong electric field strengths are generated, which can efficiently ionize and fragment molecules without the need for resonant absorption. However, the complex interaction between these pulses and biomolecular species is not well understood. To address this issue, we have studied the interaction of intense, femtosecond pulses with a number of amino acids and small peptides. Unlike previous studies, we have used neutral forms of these molecular targets, which allowed us to investigate dissociation of radical cations without the spectra being complicated by the action of mobile protons. We found fragmentation was dominated by fast, radical-initiated dissociation close to the charge site generated by the initial ionization or from subsequent ultrafast migration of this charge. Fragments with lower yields, which are useful for structural determinations, were also observed and attributed to radical migration caused by hydrogen atom transfer within the molecule.

Double slit interferometry to measure the EUV refractive indices of solids using high harmonics.

Accurate values of the extreme ultraviolet (EUV) optical properties of materials are required to make EUV optics such as filters and multilayer mirrors. The optical properties of aluminum studied in this report are required, in particular, as aluminum is used as an EUV filter material. The complex refractive index of solid aluminum and the imaginary part of the refractive index of solid iron between 17 eV and 39 eV have been measured using EUV harmonics produced from an 800 nm laser focused to 10(14) Wcm(2) in an argon gas jet impinging on a double slit interferometer.

Absolute spin calibration of an electron spin polarimeter by spin-resolved photoemission from the Au(111) surface states.

Here we report the absolute characterization of a spin polarimeter by measuring the Sherman function with high precision. These results have been obtained from the analysis of the spin and angle-resolved photoemission spectra of Au(111) surface states. The measurements have been performed with a 250 kHz repetition rate Ti:sapphire amplified laser system combined with a high energy-, angle-, and spin-resolving time-of-flight electron spectrometer.