Amin Abdolvand

Passive Q switching and self-frequency Raman conversion in a diode-pumped Yb:KGd(WO(4))(2) laser.

We report on the laser performance of a diode-pumped Yb:KGd(WO(4))(2) laser that is passively Q switched with a Cr(4+):YAG saturable absorber. Raman conversion of fundamental laser emission in the laser crystal was demonstrated. Q-switched 3.4-mu;J pulses with a pulse width of 85 ns were obtained at the 1033-nm fundamental wavelength and 0.4-mu;J pulses with a pulse width of 20 ns were produced in a first Stokes at 1139 nm.

Conical refraction Nd:KGd(WO_4)_2 laser

In 1832 Hamilton predicted conical refraction, concluding that if a beam propagates along an optic axis of a biaxial crystal, a hollow cone of light will emerge. Nearly two centuries on, cascade conical refraction involving multiple crystals has not been investigated. We empirically investigate a unique two-crystal configuration, and use this to demonstrate an ultra-efficient conical refraction Nd:KGd(WO(4))(2) laser providing multi-watt output with excellent beam quality independent of resonator design with a slope efficiency close to the theoretical maximum, offering a new route for power and brightness-scaling in solid-state bulk lasers.

Poling-assisted bleaching of metal-doped nanocomposite glass

Thermal poling of soda-lime glass which was doped with spherical or ellipsoidal silver nanoparticles has revealed what we believe to be a phenomenon of general interest in the physics of nanocomposite materials: The field-assisted dissolution of metal nanoparticles embedded in glass. Macroscopically, this phenomenon manifested itself as poling-assisted bleaching of the glass in the sense that the glass became more (or even completely) transparent under the anode. The phenomenon is physically interpreted in terms of the ionization of metal nanoclusters followed by the removal of ions from the clusters and their drift in the depth, under the action of the extremely high electric field which is created underneath the anodic surface during poling. The underlying physical mechanism is expected to offer unique opportunities for the control of structural and optical properties of nanocomposite glasses.

Electric field-assisted formation of percolated silver nanolayers inside glass.

A combination of direct current (d.c.) electric field and moderately elevated temperature is applied to a glass with embedded spherical silver nanoparticles in the near surface region. The field-assisted dissolution of silver nanoparticles leads to the formation of a layer of percolated silver clusters with modified optical properties beneath the glass surface. The distance between this produced buried layer and the surface of the sample can be controlled by the magnitude of the applied voltage. The same holds for the interferential colors observable in reflection. The presented technique is easy to implement and paves a route towards the engineering of the optical properties of metal-doped nanocomposite glasses via modification of the spatial distribution of metallic inclusions.

Metal-glass nanocomposite for optical storage of information

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.

Generation of wavelength-dependent, periodic line pattern in metal nanoparticle-containing polymer films by femtosecond laser irradiation

Thin polymer films containing metal nanoparticles were irradiated with ultrashort, linearly polarized laser pulses. As result of irradiation, nanostructural changes occur in a type of periodically arranged, line-like areas with modified particle size and shape distribution. The periodic formation in this nanocomposite material is observed only for a small filling factor range, which can be attributed to the percolation region or nearby. Transmission (also in cross section) and scanning electron microscopy were applied to investigate the obtained structure modifications. A linear dependency between the period Λ of the line structures and the laser wavelength λ (800, 528, 400, and 266nm) used with Λ∕λ≈0.70 is assumed. The structural changes and the physical mechanism of the periodic formation are discussed.

Nanosecond pulsed laser blackening of copper

Nanosecond (12 ns) pulsed laser processing of copper at 532 nm resulted in the formation of homogenously distributed, highly organized microstructures. This led to the fabrication of large area black copper substrates with absorbance of over 97% in the spectral range from 250 nm to 750 nm, and a broadband absorbance of over 80% between 750 nm and 2500 nm. Optical and chemical analyses of the fabricated black metal are presented and discussed. The employed laser is an industrially adaptable source and the presented technique for fabrication of black copper could find applications in broadband thermal radiation sources, solar energy absorbers, irradiative heat transfer devices, and thermophotovoltaics.

Generation of metal-oxide nanoparticles using continuous-wave fibre laser ablation in liquid

In recent years, laser ablation in liquid has become an increasingly important technique for the fabrication of nanoparticles (NPs). To date, only pulsed lasers have been used. This paper reports our recent studies on the generation of Ti-oxide and Ni-oxide NPs by the ablation of metal targets in aqueous environments using a high-power, high-brightness continuous-wave (cw) fibre laser at a wavelength of 1070 nm. Owing to the high and uniform irradiation, the fibre laser provides an alternative approach for NP generation with well-controlled phase, size and size distribution, along with high production rate. Characterization of the NPs, in terms of morphology, size and size distribution, chemical composition and phase structure, by means of high-resolution transmission electron microscopy (HRTEM), high-angle annular dark field (HAADF) in scanning-transmission (STEM) mode, energy-dispersive x-ray spectroscopy (EDS) and x-ray diffraction (XRD), has been presented. In addition, limitations of the cw fibre laser process have been discussed in comparison with pulsed laser process.

Poling-assisted bleaching of soda-lime float glasses containing silver nanoparticles with a decreasing filling factor across the depth

The recently discovered poling-assisted bleaching of glass with embedded silver nanoparticles has renewed the interest in thermal poling as a simple, reliable, and low-cost technique for controlling locally the surface-plasmon-resonant optical properties of metal-doped nanocomposite glasses. In the present study, the emphasis is put on the influence of the volume filling factor of metallic clusters on poling-assisted bleaching. Soda-lime silicate glass samples containing spherical silver nanoparticles with a decreasing filling factor across the depth were subject to thermal poling experiments with various poling temperatures, voltages, and times. Optical extinction spectra were measured from ultraviolet to near-infrared ranges and the surface-plasmon-resonant extinction due to silver nanoparticles (around 410nm) was modeled by the Maxwell Garnett [Philos. Trans. R. Soc. London, Ser. A 203, 385 (1904); 205, 237 (1906)] effective medium theory which was adapted in order to take into account the filling fact...

Homogenous silver-doped nanocomposite glass

Silver nanoparticles are generated in glass by a dry process. First silver ions are driven into the glass by electric field-assisted ion exchange. Subsequent annealing in air led to the formation of silver nanoparticles beneath the surface of the glass. A thin slice of the cross section of the sample was prepared. This visualization of the depth profile facilitated optical analysis of the embedded layer containing silver nanoparticles to be preformed. We observed that there were narrower plasmon bands close to the sample surface and wider plasmon bands in lower layers. It is attributed to the formation of larger nanoparticles with lower number density close to the surface and slightly smaller nanoparticles with higher number density in the depth of the sample.