Hydrogen-free DLC films has been deposited by femtosecond laser pulse onto (1 0 0) p-type silicon
substrates. The laser used for deposition has a pulse energy from 0.4mJ to1.6mJ and pulse width of about 50
fs with the repetition rate of 1 kHz. The laser intensities on the target are from 0.7×1014W/cm2 to
2.8×1014W/cm2. Uniform and wear-resistant DLC films is deposited with fs laser ablating a high purity
graphite target at room temperature in vacuum. It is shown that the films has a good hardness ranged from
20 GPa to 30 GPa. Raman spectroscopy, X-ray Photoelectron Spectroscopy and micro-hardness are used to
analyze the comprehensive performance of the films, and the results show that the films deposited at the
laser intensity of 1.4×1014W/cm2 has better hardness and a higher sp3 content. The sp3 fraction of the films is
estimated to be as high as 45.6%.
Diode lasers develop very fast and are widely used in various optical equipment. Diode laser sources produce fields that
show fundamental variations with respect to the canonical Gaussian beam. A partially coherent Lorentz model is
employed to describe the far field of a single mode diode laser beam. This paper is concerned with laser junctions
significantly narrower than the wavelength. Two lenses system are placed in front of the laser diode, so that the
diverging beam is transformed into a converging beam. The across spectral density function in the plane perpendicular to
the diode junction is considered in detail, and subsequently employed to predict the light intensity at various beam cross
sections near the focus by using the generalized Huygens diffraction integral. The intensity profile at a focused spot
produced by a partially coherent Lorentz beam is investigated and compared with that of Gaussian Schell-model beam. It
is shown that it has a simple form but fairly describes the optical field in the focal region. The theoretical results are well
fit to the practical results in this model and the variations between theory and the experiments are quite less than that of
in Gaussian beams. Since Gaussian beams have a minimum uncertainty field, i.e. it possesses the minimum achievable
angular spreading once the spatial extension is fixed. Since diode lasers produce highly diverging fields, a Gaussian
description for the transverse fields fails. In this case, our results show that partially coherent Lorentz model is a better
approximation, and the numerical simulation and discussions are given in detail.
A off-axis deposition method, which aligns the edge of the substrate to the normal of the plasma plume and
makes the edge of the plasma plume at the center of the substrate, is used to deposit large-area DLC films. The
distance between the target and the substrate and the deposition time are optimized to obtain uniform and large
area DLC films on the K9, fused silica glasses and ZnS with the diameter of 50 mm. It is shown that the thickness
uniformity of the films with off-axis deposition method is much better than that with the on-axis method. The
thickness uniformity for off-axis and on-axis deposition is compared, and the possibility for preparing large-area
uniform films is discussed. In addition, the transmission of ZnS with DLC coated is improved.
Proc. SPIE. 6028, ICO20: Lasers and Laser Technologies
KEYWORDS: Diffraction, Gaussian beams, Coherence (optics), Matrices, Laser applications, Free space, Laser beam propagation, Beam propagation method, Systems modeling, Global system for mobile communications
We investigate the twist properties of the ten-parameter family of partially coherent general anisotropic Gaussian Schell model (AGSM) beams passing through first-order optical systems. By utilizing the generalized Huygens-Fresnel diffraction integral for asymmetric first-order optical systems, the explicit twist expressions for the principal axes of intensity distribution, transverse coherence distribution and the principal curvatures of phase front in the cross-spectral density function of AGSM beams are obtained. In some special cases when the beams are the twist Gaussian Schell-Model, Gaussian Schell-Model, Li-Wolf and Gori-Guattari beams, our results reduce to well known expressions. It is shown that, under some conditions, although the ten parameters are all not zero and any one of the intensity distributions, transverse coherence distribution and the phase front has its independent principal axis, the beam spot does not twist when the beam passing through free-space. As a result, special partially coherent beams called the twisted-free ten-parameter family of partially coherent general anisotropic Gaussian Schell model (TF-AGSM) beams are introduced and their properties are discussed.
In this paper, deposition of La2/3(Ca1/3Sr2/3)1/3MnO3 thin films with femtosecond high repetition rate laser (1kHz) and low repetition rate nanosecond KrF laser (several Hz) are described. The X-ray diffraction pattern shows that the film has crystal plane orientation (100) on the LAO substrate and epitaxtial single crystal structure, and the composition analysis shows that the atomic percentage of Sr and Ca in the film is in good agreement with the target composition. The characteristics of the resistance with temperature is discussed.
The study of long-range propagation of ps UV laser pulses in atmosphere and the beam profile spatial evolution is presented. The laser used in the experiment is a dye-KrF hybrid laser with the wavelength of 248 nm, maximum pulse energy of 140 mJ and pulse width of less than 10 ps. Measurement of spatial profile of laser beam and the plasma column produced of along the propagation direction verify that the filamentation of self-guiding is 2.6 m and the diameter of the self-guiding beam is 160 μm for the incident beam energy of 40 mJ. The electron density in the self-guiding column is derived to be several times of 1015 cm-3 level using a weakly ionized model.
Femtosecond laser is suitable to machine a variety of materials, such as metals, semiconductors, polymers, oxide ceramics, silica aerogels, optical glasses, crystals, deep sea sands and even explosives because of its high peak power density and low heat affected zone. In this paper, the femtosecond laser micromachining of different materials and for different processing is presented, including structuring in optical glasses, and the cutting of metals and the deep-sea (South China Sea) sands. The laser used in the experiment is a commercial Ti:Sapphire laser with the pulse width of 50 and 100 fs, wavelength of 800 nm, maximum pulse energy up to 2 mJ and the repetition rate of 1 kHz. The evolution of material eruption as a function of the number of laser pulses and intensity is studied. The dependence of ablation rate with laser intensity and the number of the pulses is characterized by measuring the maximum laser penetration depth in different materials.
Development of precision micro-fabrication techniques for transparent materials such as crystal quartz, sapphire, silica glass is strongly desired in various industrial. During laser ablation the quality of micro-fabrication depends strongly on the optical breakdown region induced by laser irradiation. In this work, nanosecond ultraviolet laser can be used to micro-process on the surface of silica glass and microcrystal glass in air. The experiments demonstrate that number of laser pulse, scanning velocity, laser wavelength and absorption index of these materials are important factors affecting quality of micro-fabrication using ultraviolet laser.
Liquid water acts as an important role in laser processing. Water can be added on purpose gain better result: to avoid redeposition of debris, to cool the material, to increase plasma pressure or to conduct light. On the other hand water is the most common, cheap and safe medium and has an exceptionally high heat capacity. So many researches have been carried out in water-assisted laser processing. In this article, UV laser (wavelength: 355nm, pulse width: 10ns THG Nd:YAG laser) assisted processing of ceramics in air and in water is studied and compared with the processing quality in different environment.