Narrowly divergent high-energy electron beam is experimentally demonstrated during the interaction of terawatt Ti:Sa laser radiation with a nitrogen gas-cluster jet at gas pressure corresponding to the boundary of the condensation region. A collimated electron beam with an energy of up to 10 MeV and a divergence of 10 mrad at a plasma concentration of 1019 cm–3 is obtained. The use of nitrogen instead of argon or krypton significantly improves the spatial (divergence) and energy (charge and spectrum shape) properties of the generated electron beam. The formation of clusters in a supersonic jet is observed and their composition is thermodynamically analyzed.

We created a laser-plasma X-ray source based on the femtosecond fiber laser with high yield $\sim 2 \times 10^{9} \mathrm{phot} / \mathrm{s} / 2 \pi(3-12$ keV), and with a source size diameter of approximately 10 microns. The X-ray yield and the source size were optimized by using artificial intelligence, the He flow and nanosecond pre-pulse.

Results of experimental investigation of charged particles generation and X-ray emission under relativistic interaction of laser pulse with $\left(\mathrm{C}_{2} \mathrm{H}_{6}\right) \mathrm{N}$ clusters are presented. Energy spectra of protons, ions and electrons are examined, revealing few hundreds of MeV particles.

X-ray generation under interaction of relativistic laser pulses with krypton clusters has been studied. It is shown that the optimal focusing points for generating characteristic and hard bremsstrahlung are located in regions with different cluster concentrations inside the gas jet. A record (4.2 × 10–6) conversion efficiency of relativistic laser pulses into characteristic Kα (12.6 keV) has been achieved under interaction with large krypton clusters. The bremsstrahlung plasma temperature has been measured to be Te = 6 keV at an integral energy of the X-ray pulse of 3 × 109 keV/(4π pulse). The application of the designed source in time-resolved X-ray studies and in radiobiology are discussed.

A new approach is proposed to the production of high-energy ions from a cluster jet irradiated with relativistic (5×10^18 W/cm2) femtosecond laser pulses, based on the formation of mixed clusters with an Xe core surrounded by a Kr shell. The appearance of distinguished charge states of accelerated ions was registered: instead of low-charge Kr2+, Kr3+, Kr4+, Kr5+ for pure Kr clusters, there are three components Kr8+, Kr14+, Kr20+ for mixed KrXe clusters. The energy range of detected ions expands significantly: from 1–6 MeV for Kr clusters to 2–16 MeV for KrXe clusters.

A new approach is proposed to form a jet with submicron aggregates for femtosecond laser neutron generation under nonlinear interaction with relativistically intense laser pulse. Aggregates are formed through the rapid expansion into vacuum of the supercritical mixture of CO 2 + CD 3 OD (3:1). For the first time, fusion neutrons (2.45 MeV) with a peak output of 3 × 10 3 neutron/pulse/4 π and efficiency of 6 × 10 4 neutron J −1 were obtained under interaction of Ti:Sa laser pulse having 3 × 10 18 W cm −2 intensity with submicron aggregates produced from supercritical CO 2 + CD 3 OD mixture.

This paper presents a phenomenological analysis of thermodynamic parameters of a pulsed supersonic gas jet in a conical nozzle. Conditions have been found out for the condensation and formation of large krypton clusters resulting from phase transitions during adiabatic expansion of gas through the nozzle into vacuum. We have identified the phase state of the large clusters (submicron droplets consisting of ∼10 7 monomers) forming in the jet and obtained a high yield of X-rays from a cluster nanoplasma produced by femtosecond laser pulses of relativistic intensity I . It has been shown that, at I ≈ 3 × 10 18 W cm −2 , a nanoplasma consisting of large krypton clusters emits a broadband X-ray spectrum in the range 5 – 100 keV. The integrated laser to X-ray energy conversion efficiency achieved is ∼10 −5 (400 nJ), and the efficiency of characteristic K α line (12.6 keV) generation is ∼1.5 × 10 −6 (68 nJ), which corresponds to a quantum yield of ∼3 × 10 8 photons s −1 (4 π ) −1 , with a contrast of ∼25 relative to bremsstrahlung background.

In comparative experiments, it was found that the maximum efficiency of third harmonic generation (THG) in cluster nanoplasma was ∼9x10−5 and was approximately 4 times less effective than the case of THG in gas under similar experimental conditions. This result is consistent with theoretical calculations and show that THG amplitude in a gas is about an order of magnitude higher than in a cluster medium. The discrepancy between the THG efficiency in gas and clusters obtained theoretically and experimentally in discussed.

The acceleration of electrons to MeV energies from a Kr cluster jet irradiated by a relativistic (6 x 10(18) W cm(-2)) femtosecond laser pulse is studied. For the first time, the action of transform-limited laser pulse effects on the generation of hot electrons with an effective temperature (T-hot) of around 150 keV is experimentally demonstrated. The particles were accelerated in the plasma channel formed under self-focusing of the laser beam. Introducing a linear positive chirp together with pulse elongation from 50-similar to 120 fs results in substantially enhanced hot electrons flux with a growth of T-hot up to 300 keV and a maximal energy of over 2 MeV. The observed effect may be related to the strongly nonlinear propagation of the pulse through plasma, accompanied by more favorable conditions for efficient particles energy gain and pulse nonlinear compression.

Superluminescent diodes based on a separate-confinement (GaAl)As heterostructure are studied in the 850-nm spectral region. A contact p+-GaAs layer in the output sections of a narrow active channel of width 4 μm was removed and a metal contact was not deposited. These sections played the role of saturable absorbers. This design provided a significant increase in the catastrophic optical damage threshold and ensured 250 mW of output cw power at the diode facet. The power coupled out through a single-mode fibre in the case of a simplest coupling achieved 110 mW.

We present recent results on development of superluminescent diodes (SLEDs) at spectral range from 680 nm to 1300 nm, that are able to deliver 10-30 mW singlemode fiber-coupled non-coherent light. It is shown that optimization of SLED structure and facet protection/antireflection coating procedures allows to get very flat spectrum at very high fiber outputs, with very small parasitic Fabry-Perot resonances. It is also shown, that by optimization of SLED structure it is possible to widen output spectrum considerably. At 940 nm band, 70 nm FWHM spectrum is demonstrated with 5 mW SM fiber output. Coherence function of different SLEDs, and impact of residual spectral modulation and minor structure non-regularities on secondary coherence effects are discussed. The results show that SLEDs are capable to deliver same and even higher outputs than fluorescent fiber doped sources. We also discuss some SLED parameters that are important for OCT applications, like optical feedback sensitivity and SLED noise and its subtraction. Finally, some possibilities on SLED power increasing and spectrum broadening are discussed.

New highly effective potentially low-cost SLDs for fiber-optic sensor applications are reported, with strongly reduced output power on temperature dependence. Singlemode non-cooled fiber pigtailed TO-like modules have been assemled on the base of these emitters, providing 1 mW fiber output at +85 degC ambient temperature with -60 dB secondary coherence subpeaks reflectivity.

An investigation was made of the following dynamic operational regimes of three-section laser diodes based on (GaAl)As heterostructures with different connection configurations and different control signals: direct modulation of the current in the superluminescence regime and lasing under uniform injection conditions; self-modulation of the intensity (including hysteretic self-modulation bistability and chaotic spiking) and synchronisation of such modulation by a harmonic current signal; generation of picosecond optical pulses under the conditions of Q switching and mode locking in an external cavity; tuning of the emission wavelength. The investigated lasers were constructed to ensure good contact with single-mode fibre waveguides.

The properties of a three electrode GaAs laser make it particularly suitable for initialising a low coherence interferometry set-up. Three successive procedures are used to minimise the optical path difference without altering the optical set-up.

It is shown that multielectrode pumping allows a significant increase in the output power of quantum well SLDs in the broad spectrum operating regime. More than 60 nm spectral width at output power ranges from 2 to 23 mW was obtained by two-electrode pumping of the active region of AlGaAs SQW SLD. The possibility of controlling the form of the SQW SLD spectrum by multielectrode pumping and central wavelength switching of a 20 nm FWHM (Gaussian profile) over 40 nm is shown. The coherence length of the SLDs estimated using the Mandel approach is 7 mm at 2 mW output, increasing to 11 mm at 23 mW.

Theoretical and experimental investigations were made of the power, spectral, and polarisation characteristics of superluminescent diodes based on (GaAl)As heterostructures with separate confinement and a quantum-well active layer. The technical characteristics of these diodes were not inferior to those of superluminescent diodes based on traditional double-sided heterostructures. The new diodes were superior to the traditional heterostructures in respect of the half-width of the emission spectrum which was up to 100 nm, corresponding to a coherence length less than 7 μm. Test samples of light-emitting modules based on the investigated diodes were constructed.

Superluminescent diodes (SLDs) based on (AlGa)As single quantum well separate confinement heterostructures have been fabricated. The dependencies of their output power and spectrum on active channel length, pumping level and temperature were studied. Using combined pulsed/DC pumping an average spectrum width of 98nm was obtained. A visibility function FWHM of 5.5 mu m and l/e(2) width of 9.5 mu m were recorded.