Gy. Farkas

Proposal for attosecond light pulse generation using laser induced multiple-harmonic conversion processes in rare gases

Abstract A new principle of attosecond light pulse generation is suggested. The method is based on a Fourier synthesis of laser induced multiple harmonics, which all are oscillating with the same fixed phase as predicted and observed recently in rare gases. According to our calculation using published experimental data, the production of a regular sequence of ∼30–70 as duration light pulses is expected to be realizable.

High current, small divergence electron beams produced by laser‐induced surface photoelectric effect

The potential application of the laser induced linear surface photoelectric effect for high current and small divergence electron beam formation is examined. The temporal evolution of the current pulses and the angular distribution of the photoelectrons produced following KrF laser irradiation of a gold surface is studied as a function of laser intensity. A threshold laser intensity of (140±20) MW/cm2 was determined, below which the single photon photoeffect dominates any laser induced thermionic emission process. Electron current measurements for vertical and horizontal polarization of the incident laser radiation showed that the current contribution from the surface photoeffect is about three times larger than that from the volume photoeffect. Under these conditions, an angular distribution of the produced electrons of 17°±2° was determined. The estimated normalized transverse beam emittance is 20π mm mrad.

Influence of optical field emission on the nonlinear photoelectric effect induced by ultrashort laser pulses

Abstract A decrease in the order of nonlinearity of photoelectron emission from a metal cathode was found experimentally with mode-locked laser pulses at sufficiently high intensities. This phenomenon is interpreted as due to the theoretically predicted appearance of optical field emission.

Laser-induced electron emission from an Au surface irradiated by single picosecond pulses at λ=2.94 μm. The intermediate region between multiphoton and tunneling effects

The photoinduced electron emission from the surface of a solid gold target irradiated by single picosecond pulses of an erbium laser is investigated. The applied laser intensity (5–120 GW/cm2) corresponds to the intermediate interaction region between the pure multiphoton and tunnel effects, where the decisive Keldysh-parameter, γ, is in the range 1<γ<12=n0. In the light intensity region which is free of surface heating (IL<80 GW/cm2), the slope of the measured logarithmic intensity dependence of the photocurrent decreases from the n0=12 perturbative value down to n ℞ 5. Therefore the experiment shows that the Keldysh-type theories, which have recently been proved to describe correctly the ionization of atoms, are also valid to a certain extent in the case of the photoeffect in metals.

Multiphoton electron emission processes induced by different kinds of ultrashort laser pulses

Abstract Using ultrashort laser pulses of regular (gaussian shaped) time and spectral distribution, theoretically predicted, multiphoton electron emission processes have been observed. On changing this regular form of the ultrashort light pulses, however, the character of the emission process also changes, the explanation of which follows only partly from the evolution of the mode-locking train.

Linear surface photoelectric effect of gold in intense laser field as a possible high‐current electron source

Investigations were conducted on radiation‐induced electron emission processes on a gold target surface with a high‐intensity (2 MW/cm2) KrF laser (λ=248 nm). The single photon surface photoelectric emission obtained can be used for high‐current density electron sources. The measured polarization dependence of electron current shows the dominance of the surface‐type effect over that of the volume type, thereby making it possible to optimize the short, high‐density electron current creation conditions. The advantage of the grazing light incidence and the multiphoton photoeffect giving rise to a 500 A/cm2 electron current has been demonstrated.

A new effect in multiphoton photoeffect of a gold surface induced by picosecond laser pulses

A bandwidth‐limited 15‐psec laser pulse is used to induce multiphoton photoelectric emission from a gold metal cathode. The wavelength is tuned between 10 580 and 10 620 A to investigate the transition from a four‐photon to a five‐photon photocurrent j from a gold surface. This transition gives rise to a new effect marked by a dramatic change of the slope n=∂ logj/∂ logI, where I is the laser intensity.

Enhancement of ultraviolet laser plasma emission produced in a strong static electric field

Abstract Enhancement of the ultraviolet (UV) radiation (200–350 nm) emitted from a laser produced plasma created on a gold target surface in the pressure of high negative static electric field by an order of magnitude was observed. Electric field induced recombination processes are posited as a mechanism for the UV radiation enhancement.

A new type of intense CO2 laser induced electron emission from a gold surface

Abstract We describe the first experimental demonstration of a strong, short duration electron emission from a gold surface irradiated by an intense nanosecond CO 2 laser pulse (λ = 10.6 μm). The emission can neither be explained by multiphoton photoeffect, nor by pure thermionic emission. We interpret it as a dynamic optical field emission process.

Epitaxial regrowth of Ar implanted amorphous Si by laser annealing

The epitaxial regrowth of argon‐implanted self‐implantation‐produced amorphous silicon under Q‐switched ruby laser pulses is reported. It is shown that pulse annealing succeeds in producing epitaxial regrowth in the present case where equilibrium thermal annealing fails. A highly porous layer filled with spherical voids is observed by transmission electron microscopy (TEM). Four‐point probe measurements of the annealed layers exhibit a very high sheet resistance. The electrical properties are explained in terms of the unique microstructure of the pulse annealed layer.