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In this work, the generation and the characterization of high current electron beams from rough photocathodes induced by an ultraviolet excimer laser are reported. The cathodes were rough Cu disks. In order to study the influence of the cathode surface, the electron emission from different surface roughnesses was investigated. To establish the electromagnetic and geometric parameters a Rogowski coil and a new slit–slit emittance meter were used. The laser beam utilized was obtained by a mixture of Kr and Cl which generated coherent light at 222 nm. Fixing the laser energy at 0.5 mJ and the laser spot into 4 mm2, the maximum current as well as the maximum emittance value were obtained with the cathode that had the highest surface roughness which resulted in 1 A and 46 π mm mrad, respectively. A low current and a low emittance were obtained with the cathode that had the lowest roughness, namely, 410 mA and 19 π mm mrad, respectively. A quantum efficiency value of 1.2×10−4 was reached with the cathode with t...

We report on the electron emission from Cu and diamond film cathodes irradiated with two ultraviolet excimer laser beams working at 308 nm XeCl, and 222 nm KrCl. The beam emittance measurements were performed using a new experimental setup composed of two movable slit arrays. The electron beam phase space areas were determined by splitting the beam in small beamlets and measuring the beamlet direction spread via small cups and slits. The highest emission was obtained at the lowest laser wavelength. With a 4 mm2 beam spot and 0.5 mJ laser energy the maximum currents from the Cu and diamond film cathode were 370 and 410 mA, respectively, and the corresponding emittances were 18 and 27 (π mm mrad). From these values the normalized beam brightness was estimated to be 4.6×109 A(π m rad)−2 for the Cu cathode and 2.3×109 A(π m rad)−2 for the diamond cathode. By increasing the laser energy and the spot beam the maximum extracted current was 16.4 A from the Cu cathode with the KrCl laser.

Intensity-induced variations in the energy transmittivity and temporal shape of pulses emerging from a 200-μm-diameter core silica fibre have been investigated with a single-pulse XeCl laser. By coupling an XeCl laser pulse of 3mJ with a temporal width of 20 ns into a 30-m-long all-silica fibre, a total laser pulse of 1 mJ and 3 ns duration has been extracted at the fibre end. A pulse shortening larger than 80% has been observed. It is shown that the shape variations in the transmitted laser pulses are mainly due to stimulated Raman scattering processes. Substantial shape variations have been observed even at energy conversion efficiencies to the Stokes radiation of lower than 10%. The drop in energy transmittivity at higher fluences seems mainly due to two-photon absorption processes.

The performance of a long pulse XeCl laser, fitted with a negative branch unstable cavity using a phase-unifying (PU) mirror as output coupler, has been investigated. Laser beams with a divergence close to the diffraction limited value and with a relatively uniform intensity profile have been extracted by using an unstable cavity with magnification factor M = 2. It is shown that PU-unstable cavities are quite peculiar tools with respect to hard-edge unstable cavities, mainly for active media having a large cross section and requiring low magnification factors. Indeed, the beam divergence is increased by about 50% by replacing the phase-unifying mirror with a hard-edge aluminized mirror.

The performance of a high-gain, short-pulse XeCl amplifier fitted with a phase-conjugate (PC) cavity by stimulated Brillouin scattering and injected by a laser pulse provided by a XeCl oscillator without intracavity dispersive elements is investigated. A train of up to four pulses with pulse shortening was obtained from the PC cavity. The divergence of the PC cavity output beam was close to the diffraction limit and its spectral intensity distribution was equal to that provided by the free-running XeCl oscillator.

The performance of different super-Gaussian unstable resonators applied to a high-gain, short-pulse XeCl laser has been investigated. The output beam divergence measurements show that in the XeCl laser the output arises from an initial burst of spontaneous emission which is amplified as it propagates within the unstable resonator and after each round trip an output pulse with different spatial characteristics is obtained.

A XeCl laser system without dispersive elements is used to investigate near threshold reflectivity and phase-conjugation (PC) fidelity of stimulated Brillouin scattering (SBS) mirrors with SF6 as the active medium. Using different focal-length lenses to focus the broadband laser radiation into the Brillouin medium, it was found that at threshold the effective interaction length for SBS is equal to the confocal parameter and that the SBS gain is equal to its steady-state value for monochromatic pumping. High PC-fidelity values ranging from 0.8–1.0 were found under most of the experimental conditions investigated.

A stimulated Brillouin scattering mirror has been used to ‘temporally tune’ from nanoseconds to subnanoseconds the width of laser pulses generated by a free running XeCl oscillator, equipped with a super-Gaussian reflectivity unstable resonator. Pulse shortening techniques by stimulated Brillouin scattering (SBS) and by truncated SBS have been investigated. A maximum pulse shortening of about fifty has been achieved by truncated SBS.

A XeCl laser source of variable coherence length has been used to investigate stimulated Brillouin scattering in cyclohexane and methanol versus pump intensity. Peak intensity reflectivities of 48 and 55 percent have been measured in cyclohexane and methanol respectively at about 100 GW/cm2 by using a pumping beam with a bandwidth of 44 GHz. Competitive nonlinear processes reduce reflectivity at higher pump intensities. However, a poorer beam reconstruction has been observed. It has been found that the divergence of the Brillouin backscattered radiation was larger than that of the pumping beam.

An oscillator-amplifier XeCl laser system has been used to experimentally investigate the effectiveness of a liquid stimulated Brillouin scattering (SBS) mirror for correcting the spatial aberrations of broad-band laser radiation in a double-pass amplifier. It has been found that the SBS amplifier performance is strongly dependent on the intensity Ip exciting the Brillouin medium. A good beam reconstruction has been attained at Ip≤1GW/cm2, whereas highly aberrated output beams have been delivered by the SBS amplifier for Ip>1 GW/cm2. By comparing the broad-band SBS amplifier performance to that of the same amplifier with a dielectrically coated flat mirror at one end, it has been found that the use of a SBS mirror is advantageous to obtain lower divergence output beams only for low energy pump beams (

The near- and far-field performance of self filtering unstable resonators, with magnification factors | M | ranging from 5 to 133 has been investigated with an uv-preionized, discharge excited XeCl laser. The mode volume increases with | M | but the extracted energy density falls out rapidly. A decrease with | M | of the output beam optical quality and brightness has also been observed.

Self-Q switching of a XeCl laser fitted with a resonator containing a stimulated-Brillouin-scattering phase-conjugate reflector is demonstrated. Q-switched laser pulses of 0.2-mJ energy and 2.5-ns duration and with a divergence close to the diffraction limit were obtained. A spectral narrowing of the two strong lines at 307.98 and at 308.19 nm exhibited by the XeCl laser spectrum was also observed.

A gaussian reflectivity resonator of magnification M=5.2 has been used in a high-gain, short-pulse excimer laser. A good optical quality, 20 mm diameter laser beam, of 60 mJ, 18.6 ns long and with a brightness of 2.4x1013 W cm-2 sr-1 has been obtained. By decreasing the active mode volume cross section, higher optical quality laser beams have been obtained.

Confocal and non-confocal negative branch unstable resonators with an intracavity spatial filter have been applied to a high-gain short-pulse UV preionized XeCl laser. The near- and far-field radiation characteristics have been investigated in both configurations. Laser beams of larger brightness have been obtained with non-confocal schemes. A maximum beam brightness of 1.3×1014 Wcm−2Sr−1 has been achieved.

We present a very compact and very reliable laser system formed of two discharge sections both with lateral UV preionization. The discharge electrodes are contained in a single vessel and form an oscillator-amplifier system. A single spark gap switches on both circuits. By applying a generalized self-filtering unstable resonator to the oscillator and injecting the laser beam into the single pass amplifier, an output beam of 105 mJ, with a brightness of 5.5×1013 W cm−2Sr−1 has been obtained. Moreover, by applying a pulse-forming network in one discharging circuit, the duration of the discharge breakdown has been increased and output laser pulses of 40 ns FWHM, and 80 ns base width duration (at 10% points) and of energy 100 mJ are obtained.

Stimulated Brillouin scattering (SBS) of unmodified XeCl laser radiation in n‐hexane was investigated for building phase‐conjugating mirrors. It was found that the SBS mirror reflectivity could be improved by setting a holographic grating in front of the SBS mirror and by using the first order beam reflected by the grating to pump the Brillouin medium. Maximum energy and power reflectivities of 45% and 80%, respectively, were measured. The SBS mirror energy reflectivity was reduced by 45% by removing the grating. The phase conjugation fidelity of the backscattered radiation was close to one, with or without the grating.

High‐mode‐volume, good optical quality laser beams of 55 mJ, of 19 ns duration and with a brightness of 3×1013 W cm−2 Sr−1, have been extracted from a high‐gain, short‐pulse XeCl laser, with an unstable resonator using a super‐Gaussian reflectivity mirror. The misalignment angle of the output coupler to decrease the normalized output energy by 20% was 3.5 mrad.

Near-diffraction-limited laser beams of high energy have been achieved with a long-pulse (110-ns) XeCl laser fitted with a super-Gaussian unstable cavity of magnification M = 2.7. It has been found that when the super-Gaussian output coupler is replaced with a hard-edge aluminized mirror of radius equal to the super-Gaussian mirror spot size, the output laser energy is reduced by 10%, whereas the beam divergence increases more than 50%.

The authors present the output characteristics of an excimer laser (XeCl and KrCl) with delayed double UV preionisation. He- and Ne-based mixtures were used for the XeCl laser and Ne-based mixtures for the KrCl laser, at pressures up to 7*105 Pa. For both lasers, maximum output energies (1.1 J/pulse at 308 nm and 0.3 J/pulse at 222 nm) were obtained for a delay time of about 290 ns between the onset of the preionisation and the breakdown of the laser gas. At a charging voltage of 50 kV, by varying the delay time from 140 ns to 290 ns, an improvement in the output energy of 16% for the XeCl laser and 22% for the KrCl laser was obtained. The improvement in respect of a single preionisation is about 18% for the XeCl laser with the He-based mixture, and about 14% for the XeCl laser with the Ne-based mixture.

The unsaturated losses α, and the saturation intensityIs, were measured in an uv-preionized KrCl laser for optimized He and Ne based laser gas mixtures. The measurements were made as a function of the specific power loading and of the total pressure of the laser mixtures. Higher values for α andI s were found for the Ne-based laser mixture than for the He-based mixture. At 45 kV charging voltage and at 355 kPa of total pressure we measured α=0.053 cm−1 andI s =9.4MW/cm2 for the Ne based mixture, and α=0.035 cm−1 andI s =5.1MW/cm2 for the He based mixture.

An XeCl laser beam has been used to investigate stimulated Raman scattering in H2 and in various H2-foreign gas mixtures. Helium, neon, argon, and nitrogen have been tested as foreign gases. In all the investigated mixtures with 50% of H2, the energy conversion efficiency to the first Stokes (353 nm) was more than 70% higher than that obtained in H2 at the same total pressure (40 bar) and pump energy (60 mJ). The dependence of the energy conversion efficiency on pump beam divergence has also been investigated.

Backscatter lidar measurements at 355, 532, and 1064 nm combined with aerosol optical thicknesses (AOTs) from sun photometer measurements collocated in space and time were used to retrieve the vertical profiles of intensive and extensive aerosol parameters. Then, the vertical profiles of the Ångström coefficients for different wavelength pairs (Å(λ1, λ2, z)), the color ratio (CR(z)), the fine mode fraction (η(z)) at 532 nm, and the fine modal radius (R f (z)), which represent aerosol characteristic properties independent from the aerosol load, were used for typing the aerosol over the Central Mediterranean. The ability of the Ångström coefficients to identify the main aerosol types affecting the Central Mediterranean with the support of the backward trajectory analysis was first demonstrated. Three main aerosol types, which were designed as continental-polluted (CP), marine-polluted (MP), and desert-polluted (DP), were identified. We found that both the variability range and the vertical profile structure of the tested aerosol intensive parameters varied with the aerosol type. The variability range and the altitude dependence of the aerosol extinction coefficients at 355, 532, and 1064 nm, respectively, also varied with the identified aerosol types even if they are extensive aerosol parameters. DP, MP, and CP aerosols were characterized by the Å(532, 1064 nm) mean values ± 1 standard deviation equal to 0.5 ± 0.2, 1.1 ± 0.2, 1.6 ± 0.2, respectively. η(%) mean values ± 1SD were equal to 50 ± 10, 73 ± 7, and 86 ± 6 for DP, MP, and CP aerosols, respectively. The R f and CR mean values ± 1SD were equal to 0.16 ± 0.05 μm and 1.3 ± 0.3, respectively, for DP aerosols; to 0.12 ± 0.03 μm and 1.8 ± 0.4, respectively, for MP aerosols; and to 0.11 ± 0.02 μm and 1.7 ± 0.4, respectively, for CP aerosols. CP and DP aerosols were on average responsible for greater AOT and LR values, but the LR and AOT dependence on wavelength was stronger for CP than for DP aerosols. The plots of the lidar ratio values at 355 nm versus the mean columnar values of the 532-1064 nm Ångström coefficient (Å c), the fine mode radius, the fine mode fraction at 532 nm (η c), and the color ratio, respectively, furthermore revealed the greater ability of the Å c and η c values to characterize different aerosol types.

An electron‐beam transformer accelerator is described. Its high voltage terminal rises up to 1.2 MV with an input voltage of 18 kV. The maximum electron‐beam current is 16 kA; the pulse length is about 20 nsec. Aluminized Mylar anodes and foilless anodes are used. With foilless anodes the repetition rate is at present 3 pulses/sec. Pulse shape details are given and discussed to understand the behavior of the machine and its output characteristics. An improvement program is also presented.

The formation of metal silicides was studied by irradiating thin metal films deposited on Si single crystals with laser and electron beams. It was observed that in the Si/Ptsystem reactions occur at relatively low energy fluences, corresponding to temperatures well below melting point. On the basis of a numerically solved heat diffusion equation, it is shown that reaction starts when the Si/Pt interface reaches the lowest eutectic temperature of the binary Si/Pt system. The growth rate of the reacted layers is of a few m/s.

The work done on the synthesis of metal silicides by using different pulsed lasers (ruby, Nd:glass, excimer) is presented and discussed. We found that excimer lasers offer much better characteristics for annealing of metal/silicon systems in comparison to solid state lasers.

Epitaxial regrowth of ion implanted silicon and formation of metal silicides through the reaction of Si single crystals with thin deposited metal (Pt, Pd, Cr, Mo, Ti) films was obtained with different (ruby, Nd:glass, excimer) pulsed laser sources. Temperature profiles and evolutions into the samples were calculated. It was found that partial and even complete reactions of the metal films with silicon can be obtained at laser fluences lower than those needed for melting of the materials. The morphology of the irradiated surfaces was studied with a scanning electron microscope. Formation of damage ripple patterns is discussed. Epit-axial regrowth and silicide formation without surface damage of the irradiated materials was obtained by using excimer lasers.

Excitonic properties of high-quality ZnS layers grown by low-pressure metal-organic vapor-phase epitaxy have been investigated using photoluminescence and absorption spectroscopy. Comparison with theoretical models has provided accurate information on eigenstates, broadening, strain, and temperature dependence of heavy-hole, light-hole, and split-off-band exciton transitions. Finally, radiative recombination due to inelastic exciton-polariton scattering is shown under strong injection rates.