Two-color photoemission produced by femtosecond laser pulses on copper (original) (raw)
Related papers
Two-Color Two-Photon Excitation Using Femtosecond Laser Pulses
The Journal of Physical Chemistry B, 2008
The use of two-color two-photon (2c2p) excitation easily extends the wavelength range of Ti:sapphire lasers to the UV, widening the scope of its applications especially in biological sciences. We report observation of 2c2p excitation fluorescence of p-terphenyl (PTP), 2-methyl-5-t-butyl-p-quaterphenyl (DMQ) and tryptophan upon excitation with 400 and 800 nm wavelengths using the second harmonic and fundamental wavelength of a mode-locked Ti:sapphire femtosecond laser. This excitation is energetically equivalent to a one-photon excitation wavelength at 266 nm. The fluorescence signal is observed only when both wavelengths are spatially and temporally overlapping. Adjustment of the relative delay of the two laser pulses renders a cross correlation curve which is in good agreement with the pulse width of our laser. The fluorescence signal is linearly dependent on the intensity of each of the two colors but quadratically on the total incident illumination power of both colors. In fluorescence microscopy, the use of a combination of intense IR and low-intensity blue light as a substitute for UV light for excitation can have numerous advantages. Additionally, the effect of differently polarized excitation photons relative to each other is demonstrated. This offers information about different transition symmetries and yields deeper insight into the two-photon excitation process.
Physica Scripta, 2009
A short overview of the principles and applications of the two-colour two-photon (2C2P) excitation of fluorescence by using femtosecond pulses is given. Fluorescence is generated by the simultaneous absorption of an 800 nm photon and a 400 nm photon of overlapping laser beams of a titanium:sapphire laser. Two examples of its application are presented: firstly, it is used to monitor the enzymatic cleavage of bovine serum albumin (BSA) by elastase. The fluorescent amino acid tryptophan present in BSA is excited corresponding to an effective one-photon wavelength of 266 nm. Secondly, it is shown how one can utilize the different polarizations of the excited beams for determining the symmetry of the excited states of molecules, exemplarily shown for p-terphenyl in cyclohexane. Further applications and experiments for 2C2P are suggested for using it in UV-fluorescence microscopy and for determining the properties of the electronic states of biomolecules by using differently polarized photons.
Computer Optics
We have studied the nanostructuring and colorizing of the copper surface by scanning with a femtosecond laser beam with a near-Gaussian beam profile. The experimental studies were conducted using a femtosecond laser comprising a Ti:Sapphire oscillator and a multi-pass amplifier with the maximum pulse energy of 0.7 mJ, pulse frequency of 1 kHz, and pulse duration <30 fs. It is shown that the use of a short-pulsed femtosecond laser leads to the formation of wavelength scale periodic surface structures and eventually increases the brightness of the color of the copper surface. It is revealed that via reciprocally scanning the copper surface by multiple ultrashort laser pulses with a weakly asymmetric spatial energy density distribution and an energy density below the material ablation threshold, it is possible to create a combined nanostructure composed of low-spatial-frequency laser-induced periodic surface structures coated with nanoscale roughness. It is shown that relatively minor changes in the nanostructures obtained by scanning the copper surface by multiple ultrashort laser pulses can lead to a significant change in the color during surface colorizing.
Femtosecond single-electron pulses generated by two-photon photoemission close to the work function
New Journal of Physics, 2015
Diffraction and microscopy with ultrashort electron pulses can reveal atomic-scale motion during matter transformations. However, the spatiotemporal resolution is significantly limited by the achievable quality of the electron source. Here we report on the emission of femtosecond single/fewelectron pulses from a flat metal surface via two-photon photoemission at 50-100 kHz. As pump we use wavelength-tunable visible 40 fs pulses from a noncollinear optical parametric amplifier pumped by a picosecond thin-disk laser. We demonstrate the beneficial influence of photon energies close to the photocathode's work function for the coherence and duration of the electron pulses. The source's stability approaches the shot noise limit after removing second-order correlation with the driving laser power. Two-photon photoemission offers genuine advantages in minimizing emission duration and effective source size directly at the location of photoemission. It produces an unprecedented combination of coherent, ultrashort and ultrastable single/few-electron wave packets for timeresolving structural dynamics.
Picosecond UV pulses Produced by Coherent Scattering of IR Femtosecond Pulses
Journal of the Optical Society of America B
We report the observation of coherent UV light pulses by the coherent scattering of IR pulses from atomic rubidium vapor. Rubidium atoms were first excited by a 100 fs pulse from the 5S ground state to the 5D state via a two-photon transition. The atoms were then pumped by an IR pulse resonant to the 5D–12P transition. The presence of the IR pulse triggered the instantaneous emission of a UV light pulse on the 12P–5S transition. The pulse had a time duration of tens of picoseconds, which was measured by a picosecond-resolution streak camera. The temporal shape of the generated light is explained by a simplified atom–field interaction theory.
Multiphoton k-resolved photoemission from gold surface states with 800-nm femtosecond laser pulses
Physical Review B, 2014
We measure direct multiphoton photoemission of the Au(111) surface state with 800-nm laser pulses. We observe the parabolic dispersion in the angular distribution of photoelectrons having absorbed between four and seven photons. The k dispersion we measure can be explained in terms of Shockley-state replicas, with a nascent hot electrons distribution at k above the Fermi level. Moderate laser power densities, of the order of 100 GW/cm 2 , resulted in large electron yields, indicating the importance of multiphoton excitations to define the electronic and magnetic properties of matter in the first hundred femtoseconds after laser excitation.
Laser Processing and Characterization with Femtosecond Laser Pulses
Romanian Reports in …, 2010
The nonlinear interaction of femtosecond laser pulses with matter allows the physical and chemical modification of materials at micro and nano-scale. We present an experimental setup for direct laser structuring by ultra-short laser pulses using nonlinear laser absorption on various materials such as metallic film, transparent photoresists, ceramics etc. A microscope for laser processing and laser characterization was designed and constructed to be coupled with various laser systems. The laser workstation was designed to be used for different laser structuring techniques such as laser ablation, two-photon photopolymerization (TPP), laser induced forward transfer (LIFT), near field laser lithography (NFLL). The configuration of the system allows also the spectroscopic characterization of materials by two-photon excitation (TPE).
Advances in Femtosecond Optical Spectroscopy Techniques
Laser Chemistry, 1983
This paper reviews the recent advances in optical pulse measurement techniques which have made possible the investigation of ultrafast phenomena in condensed matter on a time scale of 100 femtoseconds or less. Recent results in pulse generation, amplification, white light continuum generation, and pulse compression will be discussed. In addition, applications of these pulses for measurement will be discussed.