Semiconductor laser with a biconical waveguide

The propagation losses in the fundamental mode of a bicone made of highly reflecting metal or a dielectric of large refraction were approximately estimated using Leontovich's boundary condition. A 400-fold concentration of the energy flux density lias been obtained in a cross section which is much smaller than λ. Here, the losses are 2.5% at λ = 550 nm in an Ag bicone and 12% in a semiconductor bicone with a band gap of ≈1 eV for hv larger than the band gap. The excitation efficiency of a bicone has been estimated. While not too large, it can be increased significantly using the method proposed in the present paper. The application of the optical bicone for the multiplication of a semiconductor-laser frequency is discussed. The results obtained are also of use in scanning near-field optical microscopy and in experiments on focusing laser pulses of ultrahigh power. © 2000 Plenum/Kluwer Publishing Corporation.

Picosecond laser patterning of PEDOT:PSS thin films

Picosecond pulsed laser (10.4 ps, 1064 nm, 5 and 50 kHz) patterning studies were performed, of PEDOT:PSS thin films of varying thickness deposited by spin coating on glass substrates, by ablating the films or by changing locally by laser irradiation the optical and electrical properties of the polymer. From a detailed observation of the morphology of single pulse ablated holes on the surfaces of the films, in combination with simple calculations, it is concluded that photomechanical ablation is the likely ablation mechanism of the films. The single pulse ablation thresholds were measured equal to 0.13-0.18 J/cm 2 for films with thicknesses in the region of ∼100-600 nm. The implications on ablation line patterning of the films using different fluences, scanning speeds and pulse repetition rates, were investigated systematically. Laser irradiation of the films before ablation induces a metal-insulator transition of the polymer because of the formation of charge localization due to a possible creation of molecular disorder in the polymer and shortening of its conjugation length. © 2010 Elsevier B.V. All rights reserved.

Wideband-tuneable, nanotube mode-locked, fibre laser.

Ultrashort-pulse lasers with spectral tuning capability have widespread applications in fields such as spectroscopy, biomedical research and telecommunications. Mode-locked fibre lasers are convenient and powerful sources of ultrashort pulses, and the inclusion of a broadband saturable absorber as a passive optical switch inside the laser cavity may offer tuneability over a range of wavelengths. Semiconductor saturable absorber mirrors are widely used in fibre lasers, but their operating range is typically limited to a few tens of nanometres, and their fabrication can be challenging in the 1.3-1.5 microm wavelength region used for optical communications. Single-walled carbon nanotubes are excellent saturable absorbers because of their subpicosecond recovery time, low saturation intensity, polarization insensitivity, and mechanical and environmental robustness. Here, we engineer a nanotube-polycarbonate film with a wide bandwidth (>300 nm) around 1.55 microm, and then use it to demonstrate a 2.4 ps Er(3+)-doped fibre laser that is tuneable from 1,518 to 1,558 nm. In principle, different diameters and chiralities of nanotubes could be combined to enable compact, mode-locked fibre lasers that are tuneable over a much broader range of wavelengths than other systems.