Scattering effect has great effect on machining morphology in sapphire processed by ultrashort pulse laser. On one hand, scattering leads to saturation of machining length despite the increase of pulse energy. On the other hand, scattering results in undamaged core in the elliptical damaged shell. When the laser intensity is above half the damage threshold, the electric field is scattered to 0 and doesn’t contribute to the laser intensity at latter position. The physical model which combines scattering effect, linear and nonlinear optical effects matches well with machining morphology of sapphire at different laser parameters, including pulse energies, focus positions, focal length and pulse duration. At first laser with lower pulse energy, for instance 25 μJ, processes the inner part of sapphire. During micromachining of sapphire, the focus positions move from the bottom to the top. At last the laser with higher pulse energy, 150 μJ for example, fabricates the surface. The objective lens with the focal length of 20 mm is suitable for machining sapphire and the optimal pulse duration is 950 fs.
A 10-mm-long cylindrical shell was written in neodymium doped phosphate glass by a femtosecond laser delivering
pulses with a pulse repetition of 1 kHz, energies of 90 uJ and duration of 120 fs. The pulses were focused below the glass
surface by an objective producing ablation filaments about 200 um in length. During processing, the sample was placed
on a three-dimensional (3-D) translation stage, which moved along an enclosed pattern in the horizontal plane followed
by a minor descent less than the filament length in the vertical direction. As this procedure continued, a cylinder, which
demonstrated optical waveguiding, was fabricated with a rarified periphery and densified center region due to plasmonic
expansion and outward shockwave upon laser ablation. The refractive-index contrast, propagation loss, near- and farfield
mode distribution, and microscopic fluorescence micrograph of the waveguides were measured. 1-to-N splitters
with adjustable splitting ratio were also fabricated using current approach indicating its 3-D processing flexibility.
Compared with previous femtosecond laser fabrication methods, waveguides prepared in this approach exploit both
depressed cladding and stress-induced refractive index increase in core region and show controllable mode conduction,
strong field confinement, large numerical aperture, low propagation loss, acceptable thermal stability and intact core
The optical crystal α-Al<sub>2</sub>O<sub>3</sub> has been widely used as the matrix of ruby and blue sapphire for its wide transparency, high
thermal conductivity, big scale and low cost. α-Al<sub>2</sub>O<sub>3</sub> is so hard that cutter is easily abraded. Micromachining of α-Al<sub>2</sub>O<sub>3</sub>
by ultrashort pulsed laser is superior to the traditional mechanical approach as its non-contact and cold machining
features. However, unexpected cracks on the surface of α-Al<sub>2</sub>O<sub>3</sub> are observed after femtosecond laser machining. In order
to hinder the crack source from stretching, we optimize the laser parameters accompanied with annealing. The crack-free
machining can be achieved. Three-dimensional α-Al<sub>2</sub>O<sub>3</sub> microstructures free from fracture, such as cylinder, barrel and sphere are demonstrated.
Research on change of Rayleigh range <i>Z<sub>R</sub></i> of output beams and effect of focusing characteristics caused by the dynamic process of resonator deformation especially for the HR coupler in high power CO<sub>2</sub> Laser is given in this paper. An adaptive optics system which can compensates the change of Rayleigh range <i>Z<sub>R</sub></i> was used. The real-time control of focus position was achieved.
The focusing characteristics of higher-order mode Gaussian beams in flying optics were investigated in detail. On the basis, a novel adaptive laser processing system for flying optics was developed. In the system, a lens with long focal length and two adaptive deformable mirrors controlled by hydraulic were employed. The lens was near the laser source for some distance and the two adaptive mirrors were integrated together with parabolic focusing mirror. The system has the advantages of compact structure and easy control. The system can keep the focus position and the focus radius constant for long distance laser processing.
Using a high power pulse transverse flow CO<sub>2</sub> laser developed in our lab, a series of thin Al alloy plates were successfully welded. Effects of processing parameters (beam quality, laser power, welding speed and assisting gas et al) on weldability of Al alloy plates were given. A key technique, artificial keyhole caused by the gap between two Al alloy butt plates is successfully used, which helped to break through their high reflectivity at 10.6 μm wavelength and enhanced the energy coupling efficiency. The weld thickness of Al alloy plates reached 4 mm with 3 kW CO<sub>2</sub> laser average output power. Microhardness and tensile tests showed that for some Al alloys, mechanical properties of the welds could be near or equal to base material with the artificial keyhole technique and suitable processing parameters.
Review on recent progress of laser precision microfabrication in China is given in this paper. The universal fields of the LPM mostly using short pulse and short wavelength lasers in China are as follows: new materials, advanced manufacturing technology, information technology, biological technology, medical treatment and so on, which are given priority to the development in high-tech fields in China.