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The lifetimes of the excited levels of Er3+ in ZBLAN-based glasses and glass ceramics were investigated by using time resolved spectroscopy. Upon direct excitation most of the radiative lifetimes of the excited levels do not show a dependency on the Er3+ doping level. However, for increasing Er3+ concentrations the lifetime of the thermally coupled (4S3/2+2H11/2) levels decreases significantly. For Er3+ doped glass ceramics containing BaCl2 nanocrystals the radiative lifetimes of the Er3+ levels change. For the (4S3/2+2H11/2) levels a fast component corresponding to the Er3+ doped glass and an additional slow component of a few hundred µs was found. (© 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

The influence of temperature on the laser-induced shape modification and dissolution of silver nanoparticles in glass is investigated theoretically and experimentally. Both the local transient temperature increase in close vicinity to a nanoparticle after laser pulse excitation and effects of permanent heating of the whole sample are discussed. It is shown that the heat-affected zone reaching transiently temperatures above 500 K around a nanoparticle should be limited to a few nanometers to enable the intended transformation of initially spherical nanoparticles to prolate shapes with high aspect ratio by irradiation with a few hundred laser pulses. Already relatively small temperature increase of the sample prior to or during irradiation, provided by external sample heating or temperature accumulation in the focal volume at high laser repetition rates, causes partial destruction of the nanoparticles due to increased diffusion length of the emitted Ag cations.

The shapes of initially spherical Ag nanoparticles in soda-lime glass are persistently changed using fs laser irradiation. With linearly polarized pulses, this shape transformation of the nanoparticles causes optical dichroism of the material. The intensity dependence of this effect is studied comprehensively, addressing the whole intensity range of permanent modifications as well as the influence of the number of laser pulses applied to one spot on the sample. The results are used as basis to develop a complete scenario of the possible mechanisms leading to the laser-induced shape transformation of metallic nanoparticles in glass.

Changes in the phase and element composition, tribological properties of the Zr/AISI M2 steel system after treatment with compression plasma flows are studied in this work. It was found that the treatment resulted in the formation of a mixed layer containing atoms of a coating (Zr), a substrate (M2 steel) and a plasma-forming gas (N). The zirconium concentration in the mixed layer depends on treatment parameters. The ZrN formation in the surface layer provides microhardness increase, friction coefficient decrease and enhanced thermal stability of tribological properties.

The influence of the nitrogen compression plasma flow impact on the phase and element composition and tribological properties of AISI M2 and AISI T1 high-speed steels was investigated in this work. The bank capacitor initial voltage, the number of pulses and nitrogen pressure in the vacuum chamber varied during experiments, providing the change of energy deposited in the surface layer within the limits of 5–13 J/cm 2 per pulse. X-ray diffraction analysis, Auger electron spectroscopy, Rutherford backscattering analysis, scanning electron microscopy, optical microscopy, friction coefficient and microhardness measurements were used for the characterization of the treated samples. It was found that the treatment of both types of steel resulted in austenite formation in the surface layer and carbide partial dissolution. The growth of energy deposited in the surface layer leads to the increase of thickness of the affected by treatment layer up to 24 μm and to the decrease of MC and M 6 C carbides volume fraction in the analyzed layer. Treatment leads to nitrogen penetration into the steel up to the depth of 400 nm and the redistribution of the alloying elements in the surface layer. The decrease of hardness due to dissolution of carbides was observed almost in all range of treatment parameters, thus making unsuitable the usage of the compression plasma flow treatment for high-speed steels tribological properties improvement as a stand-alone technique.

The microstructure, phase and element composition as well as mechanical properties of plasma mixed chromium/carbon steel have been investigated. Surface alloying of carbon steel with chromium has been performed with the use of the compressive plasma flow (CPF). In this technique, the action of relatively short, intense (∼100 μs and 13–18 J/cm 2 ) plasma pulses leads to a melting of the near-surface layer (∼15 μm) of the steel substrate together with the Cr film (∼2.5 μm) predeposited on it. A rapid liquid-phase mixing in the molten state occurs, leading to the formation of new phases during fast resolidification. It is observed that plasma treatment of the system results in the formation of doped austenite stabilized by chromium. There is an increase in the austenite content with the growth of both the energy density and the number of pulses. Moreover, a change of the preferred orientation of austenite, from (1 1 1) to (2 0 0), occurs with the increase of the number of pulses. Phase and structural changes result in improvement of mechanical properties.

Using the mode splitting that can be achieved by exploiting the effect of photoelasticity and the mode selection properties of coupled resonators, single- and two-frequency operation of a diode pumped cw YAG:Nd3+ laser was observed. In the two-frequency case, a regime with two orthogonal linearly polarized modes was realized. The frequency difference between the adjacent modes could be varied from 50 MHz to 8.4 GHz. A maximum laser output power of 12 mW was achieved at a pump level of 240 mW .

We start this discussion with results obtained by applying laser pulses of quite different peak intensities and ‘writing density’; the latter referring to the question of how many pulses are, on average, hitting one position on the sample.

In the previous section we have investigated the influence of laser irradiation parameters on the nanoparticles’ shape transformation; now we focus on the effects of temperature during the reshaping processes. As discussed in Chap. 3, upon absorbing the energy of the laser pulse, the NP and its surrounding matrix experience a strong temperature increase of several hundred degrees for a time window of some ten picoseconds to a few nanoseconds. The pertinent softening of the adjacent glass matrix is crucial for the NP to have some degrees of freedom for the expansion and shape changes.

Interaction of light with nanocomposites reveals novel optical phenomena indicating unrivalled optical properties of these materials. The linear and non-linear optical response of metal nanoparticles is specified by oscillations of the surface electrons in the Coulomb potential formed by the positively charged ionic core. This type of excitation is called the Surface Plasmon (SP).

In this Chapter we will discuss the influence of various irradiation wavelengths on the induced dichroism in soda-lime glass with embedded silver nanoparticles. In the previous chapter we have seen that the position of the p-polarized SP band can only be red-shifted by a limited amount (to a peak position of 530 nm when using fs laser pulses at 400 nm). Any further increase in intensity or number of pulses applied to one sample position leads to bleaching of the SP bands, which can be explained by (partial) nanoparticle destruction.

It was shown in the previous sections that the shapes of the initially spherical Ag NPs in glass can be permanently modified by femtosecond laser irradiation; that in turn leads to the optical dichroism induced in the composite glass. The induced degree of dichroism (spectral gap between the two polarized resonances), being correlated with the aspect ratio (ratio of long and short axis) of the NPs, depends on the irradiation parameters such as wavelength, peak intensity and number of laser pulses applied. We will now explore the fabrication of polarization and wavelength selective micro-devices based on metal-glass nanocomposites.

Glasses containing metallic nanoparticles exhibit very promising linear and nonlinear optical properties, mainly due to the surface plasmon resonances (SPRs) of the nanoparticles. The spectral position in the visible and near-infrared range and polarization dependence of the SPR are characteristically determined by the nanoparticles’ shapes. The focus of Ultra-Short Pulsed Laser Engineered Metal-Glass Nanocomposites is the interaction of intense ultra-short laser pulses with glass containing silver nanoparticles embedded in soda-lime glass, and nanostructural modifications in metal-glass nanocomposites induced by such laser pulses. In order to provide a comprehensive physical picture of the processes leading to laser-induced persistent shape transformation of the nanoparticles, series of experimental results investigating the dependences of laser assisted shape modifications of nanoparticles with laser pulse intensity, excitation wavelength, temperature are considered. In addition, the resulting local optical dichroism allows producing very flexibly polarizing optical (sub-) microstructures with well-specified optical properties. The achieved considerable progress towards technological application of this technique, in particular also for long-term optical data storage, is also discussed.

This chapter is dedicated to the general understanding of laser pulse interaction with metal nanoparticles. The aim is to collect all physical processes, which may occur when the laser pulse starts to interact with nanoparticles, as well as all later events and mechanisms, which are triggered by this interaction.

Spherical silver nanoparticles (NPs) of 30 nm diameter embedded in soda-lime glass were uniformly reshaped (elongated) after irradiation by a linearly polarised 250 fs pulsed laser operating within the NPs' surface plasmon resonance band. We observed second harmonic generation (SHG) and multiphoton-absorption-induced luminescence (MAIL) in the embedded laser-reshaped NPs upon picosecond (10 ps) pulsed laser excitation at 1064 nm. A complementary study of SHG and MAIL was conducted in soda-lime glass containing embedded, mechanically-reshaped silver NPs of a similar elongation ratio (aspect ratio) to the laser-reshaped NPs. This supports the notion that the observed difference in SHG and MAIL in the studied nanocomposite systems is due to the shape modification mechanism. The discrete dipole approximation method was used to assess the absorption and scattering cross-sections of the reshaped NPs with different elongation ratios.

Four widely used electromagnetic field solvers are applied to the problem of scattering by a spherical or spheroidal silver nanoparticle in glass. The solvers are tested in a frequency range where the imaginary part of the scatterer refractive index is relatively large. The scattering efficiencies and near-field results obtained by the different methods are compared to each other, as well as to recent experiments on laser-induced shape transformation of silver nanoparticles in glass.

The lifetimes of the excited levels of Er3+ in ZBLAN-based glasses and glass ceramics were investigated by using time resolved spectroscopy. Upon direct excitation most of the radiative lifetimes of the excited levels do not show a dependency on the Er3+ doping level. However, for increasing Er3+ concentrations the lifetime of the thermally coupled (4S3/2+2H11/2) levels decreases significantly. For Er3+ doped glass ceramics containing BaCl2 nanocrystals the radiative lifetimes of the Er3+ levels change. For the (4S3/2+2H11/2) levels a fast component corresponding to the Er3+ doped glass and an additional slow component of a few hundred s was found.

By irradiating spherical metal nanoparticles embedded in glass with several hundred ultrashort laser pulses at peak intensities of 0.2-1.5 TWcm(2), dichroic microstructures can be written in these nanocomposite materials. The underlying mechanism is transformation of the nanoparticles to prolate shapes. Using a single wavelength, the maximum aspect ratio achievable with this process is limited by partial destruction of particles. Here we show that this limitation can be overcome by simultaneous irradiation with different wavelengths. In particular, adding a relatively weak intensity at 800 nm to the main irradiation at 532 nm increases the maximum aspect ratio of Ag nanoparticles and the resulting separation between polarized surface plasmon bands dramatically. These effects are explained by the efficiency of electric field enhancement in the vicinity of nanoparticles, which influences the directed photoionization needed for particle shape transformation.

Laser-induced permanent shape transformation dynamics of glass-embedded silver nanoparticles is investigated by a pulse-pair irradiation technique, where the nanoparticles are irradiated by pairs of time-delayed femtosecond laser pulses. The temporal evolution of surface plasmon extinction bands is obtained up to a time delay of 1 ns. We find that the aspect ratio of the modified nanoparticles, i.e., the observed dichroism, reduces rapidly to a minimum level within 20 ps after the laser irradiation. From that interpulse delay onward, the resulting aspect ratio stays at that minimum level until 100 ps. Subsequently, for longer time delays, the aspect ratio increases again until 1 ns. Temperature modeling of the nanoparticle-glass system gives evidence that the intermediately reduced dichroism is due to the high diffusion mobility that emitted silver ions can possess within a shell of heated glass around the nanoparticle, in a time window of 100 ps. For longer time delays the size of the heated glass shell gets reduced, thereby limiting the range of ionic diffusion. The theoretical estimations confirm the experimental results and suggest that the nanoparticle shape changes depend strongly on the thermal situation induced to the surrounding glass.

We investigate the possibility of preparation of laser-induced dichroism in composite glasses with a high concentration of silver nanoparticles. A detailed analysis based on the Maxwell-Garnett theory and experimental results shows that particles at different volume fractions react differently to the same laser irradiation parameters. Based on these findings, we demonstrate that a well-defined sequence of multiple irradiation and intermediate annealing can maximize the particles' aspect ratio and avoid unwanted partial destruction. The proposed irradiation technique permits production of micropolarizing structures with high polarization contrast in the visible and near-IR regions.

Bimetallic, initially spherical Ag/Au nanoparticles in glass prepared by ion implantation have been irradiated with intense femtosecond laser pulses at intensities still below the damage threshold of the material surface. This high-intensity laser processing produces dichroism in the irradiated region, which can be assigned to the observed anisotropic nanoparticle shapes with preferential orientation of the longer particle axis along the direction of laser polarization. In addition, the particle sizes have considerably been increased upon processing.

The shapes of initially spherical Ag nanoparticles in glass were permanently changed by fs laser irradiation. This shape transformation of the nanoparticles results in an optical dichroism of the material, strongly depending on the actual irradiation parameters such as intensity, number of pulses per irradiated spot and laser wavelength. The proposed technique allows modifying the optical properties of glass containing metallic nanoparticles and can be used for the production of dichroic or polarizing microstructures in the visible and near infrared region with high polarization contrast.

Irradiation of spherical silver nanoparticles in glass by linearly-polarized intense femtosecond laser pulses close to the surface plasmon resonance results in irreversible shape transformations. In this context, the spectral positions of plasmon resonances as a function of particle size and basic shapes are well-understood theoretically and experimentally; however, the dynamical information regarding the laser-induced shape transformation mechanisms is still a matter of interest. To investigate these dynamics we introduce a single-color double-pulse experiment, where the sample is irradiated by two time-delayed pulses of equal intensity. Different nanoparticle shape elongations can be produced depending on the delay between two irradiating pulses. Analyzing the resultant shifts of absorption bands for each delay gives valuable information on the evolution of nanoparticle shape changes. Possible shape modifying mechanisms including nanoparticle ionization, extreme lattice heating and excess energy transfer from the hot nanoparticle to the glass matrix are observed and discussed.

Femtosecond laser pulses tailored with closed-loop, optimal control feedback were used to excite oscillations in C60 with large amplitude by coherent heating of nuclear motion. A characteristic pulse sequence results in significant enhancement of C2 evaporation, a typical energy loss channel of vibrationally hot C60. The separation between subsequent pulses in combination with complementary two-color pump-probe data and time-dependent density functional theory calculations give direct information on the multielectron excitation via the t(1g) resonance followed by efficient coupling to the radial symmetric a(g)(1) breathing mode.

The results of studying changes in physical and mechanical properties of coating-substrate systems subjected to the compression plasma flow are presented. The possibility for doping the substrate both with pre-deposited coating components and with plasma-forming substance during liquid-phase mixing and resolidification of near-surface layers melted by the compression plasma flow is shown. Представлено результати досліджень зміни фізико-механічних властивостей систем покриття-підкладка при впливі на них компресійним плазмовим потоком. Продемонстровано можливість легування матеріалу підкладки як компонентом попередньо нанесеного покриття, так і робочою речовиною плазми, у процесі рідкофазного перемішування і перезатвердіння розплавлених під дією компресійного плазмового потоку приповерхніх шарів. Представлены результаты исследований изменения физико-механических свойств систем покрытие- подложка при воздействии на них компрессионным плазменным потоком. Продемонстрирована возможность легирования материала подложки как компонентом предварительно нанесенного покрытия, так и рабочим веществом плазмы, в процессе жидкофазного перемешивания и перезатвердевания расплавленных под действием компрессионного плазменного потока приповерхностных слоев.

We demonstrate an all-optical data storage and readout technique on a medium that has proved to be stable over centuries—glass containing metallic nanoparticles. Using ultra-short laser pulses to persistently change the shapes of the nanoparticles dependent of the laser polarization, well-defined local dichroism in the focal volume can be produced. The latter could be utilized for multi-bit encoding in spot sizes down to the diffraction limit, where the information can be read out very fast by wavelength- and polarization-sensitive detection of the transmitted light. The storage capacity of the proposed technique is comparable with that of blu-ray discs.