A polar-coordinate optical encoder that can realize synchronous measurement of angular and radial displacements is introduced. It has potential application in concurrent monitoring of radial and angular motions for rotating spindles and in real-time detection and compensation of eccentricity error for rotary stages. We explain its operating principle and develop a prototype. Experimental results demonstrate the feasibility and effectiveness of the proposed optical encoder in polar-coordinate displacement measurement.
In a high-energy chirped-pulse-amplified laser system, grating tiling technology provides an effective means to increase the aperture of the gratings and to scale the energy and irradiance of short-pulse lasers. The difficulties lie in controlling tiling errors accurately between the sub-gratings and keeping long time stability. In this paper, a two-pass full-tiled grating-compressor (TGC) with real- time control unit is developed for the first time. The far-field distributions of the 0<sup>th </sup>order and -1 <sup>st</sup> order diffracted beams of the two pairs of tiled gratings are monitored by the same CCD system, with the main laser chain being not disturbed. In this way, we realize online real-time control of tiling errors. Through a method of locking the far-field image to compensating the temporal drift, we can realize the automation of the assembly. The TGC has successfully applied in the multi-function XGIII laser facility, and focusing focal spot and output pulse width are obtained.
Linear encoder composed of main and index scales has an extensive application in the field of modern precision measurement. The main scale is the key component of linear encoder as measuring basis. In this article, the continuous roller imprint technology is applied to the manufacturing of the main scale, this method can realize the high efficiency and low cost manufacturing of the ultra-long main scale. By means of the plastic deformation of the soft metal film substrate, the grating microstructure on the surface of the cylinder mold is replicated to the soft metal film substrate directly. Through the high precision control of continuous rotational motion of the mold, ultra-long high precision grating microstructure is obtained. This paper mainly discusses the manufacturing process of the high precision cylinder mold and the effects of the roller imprint pressure and roller rotation speed on the imprint replication quality. The above process parameters were optimized to manufacture the high quality main scale. At last, the reading test of a linear encoder contains the main scale made by the above method was conducted to evaluate its measurement accuracy, the result demonstrated the feasibility of the continuous roller imprint method.
A novel multistep loading and demolding process in nanoimprint lithography (NIL) with a soft mold is developed to fabricate 3-D micro- or nanoscale cathode structures in polymer photovoltaic (PPV) devices. Experiments show that this new NIL process, called distortion reduction by pressure releasing (DRPR) and two-step curing method for the demolding process, can reduce and avoid the distortions of the imprint mold and wafer stage, and through the two-step curing method, the transformation of resist from liquid to solid state can be controlled, which is helpful to decrease the demolding force and avoid some defects caused by "blind" demolding. With this new NIL process, the main replicating error caused by distortions and blind demolding can be limited effectively, and the micro- or nanoscale cathode structures in PPV devices can be fabricated with high fidelity to the imprint mold, which can improve the power conversion efficiency of PPV.
A simple and high-accuracy alignment measurement method based on a moiré fringe pattern is proposed. It involves relative rotation positioning and relative linear displacement measurement. Taking full advantage of the magnification effect of moiré fringe in angular and linear displacement, the relative rotation between the template and the wafer is determined first by measuring the inclination of the moiré fringe, and then the relative linear displacement between them is acquired by evaluating the spatial phase shift of two matched moiré fringes. The frequency components in the orthogonal directions of the fringe image obtained by a fast Fourier transform (FFT) and zooming process are used to measure the inclination of the moiré fringe. By selecting different orthogonal directions, a moiré fringe with any inclination can be measured accurately. When gratings are adjusted to parallel, a frequency-domain analysis is also used to extract the spatial phase of fringes at a given frequency. According to the relationship between spatial phase and linear displacement, the misalignment is detected. In experiments, the repeatability for the misalignment measurement has reached 4.8 nm (3).