Vibration-assisted cutting is an important technology with better performance in manufacturing micro-scaled components, compared with conventional cutting technology. This article first illustrates the development of vibration-assisted micro-milling device which is made based on piezoelectric plates and shows different vibration types with vibration principle of this device. It is then tested stable to output vibration with a frequency accuracy of 100 Hz and an amplitude accuracy of 100 nm. Two groups of experiments in micro-milling 6061 aluminum alloy are carried out. Compared with conventional micro-milling, using vibration assist is verified more effective in improving surface integrity and quality. Furthermore, with a proposed method of characterizing exit-burr size, the influences of vibration frequency and amplitude on surface roughness and exit-burr size are discussed. As a result, the mean surface roughness is found positive related to vibration frequency and negative related to vibration amplitude in most of the study range. To make guidance on optimizing vibration machining parameters, cubic polynomial fitting with 95% prediction interval is of enough accuracy.
Particular attention has been given to updatable or dynamic holographic displays in recent years. The absence of ideal recording materials hampered the realization of their commercial applications. A lithium niobate crystal codoped with 1.0 mol. % bismuth and 6.0 mol. % magnesium has been grown with a diameter of 2-in. A moderately large saturation diffraction efficiency of 26% can be achieved, which corresponds to a refractive index change of 2.45 × 10−5. However, the photorefractive response time turns out to be only 13 ms, and the photorefractive sensitivity reaches 1.63 × 102 cm/J. This is by a factor of 104 larger than the one of congruent lithium niobate. The codoped crystal was used to demonstrate a real-time holographic display with a refresh rate of 30 Hz, which is a significant step forward for inorganic crystals in holographic display applications. Band structure calculations indicate that the dopants influence the charge distribution of the oxygen atoms which may be the clue to the origin of their excellent properties.
Laser has been widely used in many aspects, by now it is difficult to get each frequency that we want, and frequency conversion is an effective way to obtain different frequency laser through a nonlinear optical crystal. MgO-doped LiNbO3 (Mg:LN) crystal has usually been used for second harmonic generation (SHG) through temperature-matching configuration with a stove, till now a room temperature 90° phase-matching is still lacking. Here we find that the SHG of Nd:YAG laser is achieved at 26.1 °C while the optical damage resistance is higher than 6.5 MW/cm2 in the ZrO2 and MgO co-doped LiNbO3 (Zr,Mg:LN) crystal. Moreover, the monotonic decrease of phase-matching temperature is firstly found with the increase of doping concentration. These unusual properties may be attributed to the formation of + defect pairs. Our work suggests that Zr,Mg:LN crystal may be an attractive candidate for nonlinear optical applications.
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