Optical Review
The development of a portable line-shaping optical system for silicon surface treatment
Fri, 2013-03-01 02:00 — GuestAbstract
This study proposes a beam shaper for converting a circle beam profile generated with a Gaussian intensity distribution by an 808 nm diode laser into a line beam profile for silicon surface treatment applications. To produce a hand-held and low-cost device with a large spot-size laser, this study uses a portable optical system consisting of a diode laser source, a collimator, a cylindrical lens, and a plano-convex lens to generate an approximately 40 × 3:5mm2 line beam profile at a working distance of 200 mm. The silicon surface treated by the line-shaped laser beam has significantly reduced reflectance spectra. The proposed system is also suitable for the surface cleaning of materials.
Blue laser lithography for making antireflective submicron structures on silicon
Fri, 2013-03-01 02:00 — GuestAbstract
The application of blue laser lithography for creating antireflective submicron structures on a crystalline silicon substrate was evaluated. The assembled blue laser lithography system was obtained by modifying a commercial blue laser optical pickup head and consisting of a 405-nm-wavelength blue laser and a 0.85-numerical-aperture objective lens. Si substrates were patterned with submicron column patterns of various periods and aspect ratios by blue laser lithography using a sputtered Ge-Sb-Sn-O layer as a resist. The reflectance of the patterned Si substrate decreased to 3% on average in the 300–1000 nm wavelength range, with a low sensitivity to the angle of incident light. Such patterned substrates showed potential for application in crystalline Si solar cells.
Development of portable laser machining system for laser writing applications
Fri, 2013-03-01 02:00 — GuestAbstract
This study presents a portable laser machining system that consists of a fiber-optic diode laser source with a wavelength of 808 nm, optic/opto-mechanical components, a laser scanning module, and a laser energy control module. The laser beam quality was measured at different operation frequencies during system evaluation. The experimental results of beam profile evaluation indicate that the enlarged collimated beam was the TEM00 mode with a roundness of approximately of 96%. The output laser power level increased as the pulse frequency increased during laser power evaluation. To control the rotating angle of the galvanometric scanning system, the deflective angle was adjusted using a 0.192 voltage to obtain a deflective value of 1mm and the maximum scan field of 100 × 100mm2. The laser source operated at different frequencies, with pulse widths ranging from 530 to 48 μs. Finally, the proposed machine can also be used for black thick paper laser writing applications.
On enhanced tuning capabilities of external cavity lasers using acousto-optic modulators
Tue, 2012-10-02 19:27 — Guest
of intra-cavity acousto-optic modulators (AOM) has been developed and tested. Using a method called “mode shaking” a nearly
continuously laser tuning over a frequency range of 186 GHz (0.279 nm) within a time interval of 20 ms has been achieved.
A further method called “far laser frequency jump” allows frequency changes of up to 1080 GHz (1.6 nm) between two spectral
regions of the diode laser emission range within about 50 μs.
Quality factor of circular laser diode beam tailored by optical interference
Tue, 2012-10-02 19:27 — Guest
The far and near-field patterns were analyzed by numerical calculations based on Huygens’ integral. An almost circular tailored
beam was calculated to have a quality factor as low as 1.08. This beam-shaping technique was experimentally demonstrated using
a commercial 640 nm laser diode and a mirror-polished GaAs substrate. The optical beam tailored by Lloyd’s mirror interference
was nearly circular and its beam quality factor was measured to be 1.24. Although this measured beam quality factor is slightly
higher than the numerically calculated one, it is acceptably low.
Compensation for the thermal effect in the second-harmonic generation of a Q-switched nanosecond-kilohertz Nd:YVO4 laser
Tue, 2012-10-02 19:27 — Guest
phase-matching second-harmonic generation of a Q-switched Nd:YVO4 laser with a high repetition rate. The thermal effect can be effectively compensated for by appropriately changing the phase-matching
angle with respect to the surrounding temperature of a nonlinear optical crystal. A stable wavelength conversion from the
1064 nm fundamental to the 532 nm second harmonic in a type-I critical phase-matching lithium triborate crystal is experimentally
achieved and the corresponding conversion efficiency up to 70% is obtained.
Ultrashort pulse generation using fiber FM laser
Tue, 2012-10-02 19:27 — Guest
realized using a fiber ring with an internal phase modulator and an erbium-doped fiber amplifier. To compress FM laser pulses,
an external dispersive single-mode fiber is employed. Furthermore, by external intensity modulation, the pulse background
is removed. The background ratio of the generated ultrashort pulse is calculated and compared with the experimental results.
The experimental results show an output optical pulse width of 1.77 ps and a spectral bandwidth of 0.5 THz.
Simultaneous measurement of surface shape and absolute optical thickness of a glass plate by wavelength tuning phase-shifting interferometry
Mon, 2012-07-30 07:33 — Guest
by three-surface interferometry using a wavelength tuning Fizeau interferometer. The wavelength of a tunable diode laser is
scanned linearly from 632 to 642 nm, at which the initial and the final phases of the interference fringes for the surface
shape and for the optical thickness were separated and measured by a tunable phase-shifting technique. The number of phase
variations in the interference fringes during the scanning is counted by discrete Fourier analysis, in which systematic errors
caused by a nonlinearity in the wavelength scanning is corrected by a correlation analysis between the observed and theoretical
interference fringes. Experimental results demonstrate that the systematic errors in the measured value were 15 nm for the
surface shape and 0.6 μm for the absolute optical thickness.
Development of a double-sided micro lens array for micro laser projector application
Mon, 2012-07-30 07:33 — Guest
For commercial mass production, it is necessary to investigate the concurrent engineering of optical design, mold fabrication,
and plastic injection molding at once. This experiment based the design of the micro lens array on the scalar diffraction
theory. The proposed DSMLA can simultaneously shape red, green, and blue laser beams into a uniform projection pattern. An
ultra precision diamond turning machine using a slow tool servo method fabricated the mold. The study considered optical design
constraints from the feedback of mold fabrication and plastic injection molding, measuring and comparing fabricated samples
with calculated results. Experimental results show that the fabricated DSMLAs achieve the desired function and application
feasibility for micro laser projectors.
Design for directional emitter based on self-collimation photonic crystal by adding two-layer dielectric rods
Mon, 2012-07-30 07:32 — Guest
photonic crystal (PC). The structure is composed of a two-dimensional (2D) photonic crystal and two-layer dielectric rods.
The finite-difference time-domain (FDTD) simulations show that the emission properties are sensitive to the distance between
photonic crystal and two-layer dielectric rods. By adjusting the relative position of the two-layer dielectric rods, highly
efficient beaming emission can be realized.
