Dependence of Monocrystalline Sapphire Dicing on Crystal Orientation Using Picosecond Laser Bessel Beams.

Dicing is a critical step in the manufacturing process for the application of sapphire. In this work, the dependence of sapphire dicing on crystal orientation using picosecond Bessel laser beam drilling combined with mechanical cleavage was studied. By using the above method, linear cleaving with on debris and zero tapers was realized for the A1, A2, C1, C2, and M1 orientations, except for the M2 orientation.

Efficient Semi-Transparent Wide-Bandgap Perovskite Solar Cells Enabled by Pure-Chloride 2D-Perovskite Passivation.

Wide-bandgap (WBG) perovskite solar cells suffer from severe non-radiative recombination and exhibit relatively large open-circuit voltage (V) deficits, limiting their photovoltaic performance. Here, we address these issues by in-situ forming a well-defined 2D perovskite (PMA)PbCl (phenmethylammonium is referred to as PMA) passivation layer on top of the WBG active layer. The 2D layer with highly pure dimensionality and halide components is realized by intentionally tailoring the side-chain substituent at the aryl ring of the post-treatment reagent.

Automated screening of COVID-19 using two-dimensional variational mode decomposition and locally linear embedding.

In order to aid imaging physicians to effectively screen chest radiography medical images for presence of Coronavirus Disease 2019 (COVID-19), a novel computer aided diagnosis technology for automatic processing of COVID-19 images is proposed based on two-dimensional variational mode decomposition (2D-VMD) and locally linear embedding (LLE). 2D-VMD algorithm is used to decompose normal and COVID-19 images, and then feature extraction of intrinsic mode functions (IMFs) using Gabor filter. To better extract low-dimensional parameters which are useful for COVID-19 diagnosis, the performance of two dimensionality reduction techniques of principal component analysis (PCA) and LLE are compared, and the LLE is shown to offer satisfactory effect of dimension reduction.

Non-resonant piezoelectric linear motor with alternating normal contact force.

A non-resonant piezoelectric linear motor with alternating normal contact force is developed to realize a piezoelectric linear motor with high precision, large stroke, and strong thrust. The motor employs four piezoelectric stacks to excite the non-resonant state vibration of two driving feet, which alternately push the mover to generate unidirectional motion. Through the analysis of the working principle of the motor, the structure of the motor is designed and manufactured.

Ablation characteristics and material removal mechanisms of a single-crystal diamond processed by nanosecond or picosecond lasers.

The microstructures on a diamond surface have attracted extensive attention in microelectronics, ultra-precision machining tools, and optical elements, etc. In this work, microgrooves were fabricated on a single-crystal diamond surface using ultraviolet nanosecond or infrared picosecond laser pulses. The surface and internal morphologies of the microgrooves were characterized.

Mueller matrix ellipsometer based on discrete-angle rotating Fresnel rhomb compensators.

A spectroscopic Mueller matrix ellipsometer based on two rotating Fresnel rhomb compensators with a nearly achromatic response and optimal retardance is described. In this instrument, the compensators rotate in a discrete manner instead of continuously rotating, and this allows for a well-conditioned measurement even for low intensity samples. Moreover, in this configuration, the exposure time of the CCD detector can be varied within orders of magnitude without interfering with the dynamics of the compensator rotation.

Model-free determination of the birefringence and dichroism in c-cut crystals from transmission ellipsometry measurements.

In this work, we derive closed-form expressions for determination of the linear birefringence and linear dichroism of uniaxial crystals utilizing transmission ellipsometry measurements at small angles of incidence in $ c $c-cut crystal substrates. The model-free method we use is an algebraic generalization of the method reported in Appl. Opt.

Method of thickness measurement for transparent specimens with chromatic confocal microscopy.

In this paper, a new method for measuring the thickness of transparent specimens using chromatic confocal microscopy (CCM) is presented. The conventional CCM thickness measurement model relies on capturing the focal points on the upper and lower surfaces of a transparent specimen. This model has strict specimen placement tolerance and a limited measurement range.