A silicon steel sheet is proposed in this paper to work as a magnetic field concentrator to enhance the sensitivity of a Faraday effect based magnetic field sensor using a dual-polarization fiber grating laser. When the silicon steel sheet is placed close to the cavity of the fiber grating laser, the magnetic field is concentrated around the silicon steel sheet and hence the fiber grating laser experience stronger magnetic field than the case without the silicon steel sheet, which results in a larger magnetic field induced beat note frequency change after photodetection of the two orthogonally polarized laser outputs. With the same axial magnetic field, the experiment results confirm that the sensitivity of the sensor with a silicon steel sheet is improved over the one without a silicon steel sheet, which validates our proposal.
This paper deals with the microstructure of the generated crystals in borate glass by femtosecond laser irradiation, Raman spectroscopy was used to study the distribution of the high temperature and low temperature phases of barium metaborate crystals produced in the borate glass, and the mechanism was discussed.
We demonstrate experimentally fabrication of optical elements with femtosecond pulses. The laser source we adopted is a low power Ti: sapphire laser oscillator, with a central wavelength of 790 nm and pulse duration of 100 fs. Positive-photoresist-film-coated glass substrate acts as the sacrificial material. Due to the extreme high intensity of the tightly focused femtosecond laser beam, nonlinear processing occurred between photoresist and the laser pulses, which enable the sub-micron feature processing. In the experiments, we use a translational stage that is controlled by a computer to accurately move for fabrication of optical elements with high precision. Various gratings and phase plates are fabricated by this method. The obtained gratings patterns are checked with a conventional optical microscopy. The fabricating widths and depths are measured with the Taylor Hobson equipment. With the same method, photomask for microelectronics can also be fabricated. From the experimental results, we see that a high processing precision and the feature size exceeding the diffraction limit can be achieved with this method. This technique can be applied to the fields of microoptics and microelectronics. The mechanism between femtosecond laser and photoresist is also investigated. The processing mechanics is considered as laser ablation and nonlinear two-photon absorption phenomenon. Fabrication of optical elements with femtosecond laser reflects a new trend for fabrication of microoptical elements.
In fabrication of a fine optical element, femtosecond laser is an attractive experimental tool because it avoids the splutter effect to damage the nearby lines. However, the wavelength of the usual Ti:sapphire laser is insensitive to the widely-used photoresist in microlithographic industry. In this paper, we introduce a new method with femtosecond doubled-frequency laser by use of a BBO crystal to fabricate optical gratings and chromium photomasks. The laser source is the Ti:sapphire laser with a central wavelength of 790 nm and its doubled-frequency laser is obtained through the BBO crystal whose wavelength (395nm) is within the sensitive exposure range of the photoresist. This enables us to fabricate fine optical elements with the normal photolithographic technique. In the experiment, we use a translator that is controlled by a computer to accurately move for fabrication of optical elements with high precision. In contrast to the other techniques, our approach has the higher quality and precision, for femtosecond laser works faster than the material’s thermal diffusion, i.e., without splutter effect that yields the clear edge of the optical element. Moreover, it also makes the fabrication processing simplified. Experiments are given to verify that this method should be highly interesting for the fabrication of fine binary optical elements.
High temperature phase transition of (beta) -BaB<SUB>2</SUB>O<SUB>4</SUB> (BBO) and K<SUB>3</SUB>Li<SUB>12-x</SUB>Nb<SUB>5+x</SUB>O<SUB>15+2x</SUB> (KLN) crystals are studied in detail by using high temperature Raman scattering. The temperature increasing of the crystals due to the increasing of the incident laser power during the frequency doubling process and the influence on the structure of the crystals are analyzed. It is the first time that the relationship between the phase transition and the frequency doubling is studied by high temperature Raman spectra. The opinion of phase transition having effect on frequency doubling is given out.
We have studied the passivation of superconducting YBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7</SUB> (YBCO) films by diamond-like carbon (DLC) films using ion implantation and laser irradiation techniques. The experiment suggests that the surface layers of the YBCO films are covered by a DLC structure and critical temperature (Tc) measurements have confirmed the absence of any significant degradation after these treatments. The DLC layer successfully protects the superconducting films from environmental effect.
Preparation of diamondlike carbon films (DLC) from various kinds of organic Langmuir- Blodgett (LB) films by laser light irradiation is reported. The properties of DLC films is discussed. Using surface enhanced Raman scattering techniques, DLC films were analyzed during formation. These films are expected to be very promising for various applications.
This paper reports the experimental results on using Langmuir—Blodgett (LB) films as spacer layers between molecules and metal surface to study electromagnetic enhancement mechanisms of Surface Enhanced Raman Scattering (SERS), and to measure the change of SERS intensity with spacer layer thickness. In pyridine + KCL/LB films/Ag films configuration, the experimental results indicate SERS effect exists when the spacer layer thickness is 5 nm, and eventually it becomes unobservable with 15 nm thickness. The experiments supported the idea that the enhancement arises from an electromagnetic mechanism,