Toshio Akatsu

Laser measurement system for precise and fast positioning

A laser measurement system for precise and fast positioning of an object has been developed. When the object speed is low, the movement of the object is measured by comparing the phase change of a light beam reflected by the object with the phase modulated by an electro-optic crystal (an active device by which the optical phase can be controlled by the application of a voltage). When the object speed is high, the movement is measured by a fringe counting technique. The system achieves an accuracy of 4 nm and a maximum allowable measurement speed of 1100 mm/s.

Characteristics of electro-optic crystals for laser displacement sensor.

We are developing a laser displacement sensor which can be sued for XY-Stage positioning for example. The principle of this sensor is the interference method. It modulates the phase of the reflecting beam form the object by electro-optic crystals, and measures shift of the phase of measurement beam by comparison with that of modulated reference beam. The resolution of this sensor is 5nm, and the possible measurement speed is 1000 mm/s. We also investigated some of important characteristics of E-O Crystals on which the resolution of this sensor depends, and confirmed that they were adequate for our sensor.

A Laser Measurement System For Precise And Fast Positioning

A laser measurement system for precise and fast positioning of an object has been developed. When the speed is low, the movement of the object is measured by comparing the phase change of a light reflected by the object with the phase modulated by an electro-optic crystal (an active device by which the optical phase can be controlled by applying a voltage thereto). When the speed is high the movement is measured using a fringe counting technique. The system achieved an accuracy of 4nm, and a maximum allowable measurement speed of 1100mm/s.

Dynamic Motion Measurement Using Digital TV Speckle Interferometry

A new electronic speckle pattern interferometry technique (ESPI) has been developed and is used for non-contact examination of the head-tape interface in a revolving head configuration of a video tape recorder (VTR). Dynamic tape motion is measured by illuminating the surface of the tape with a pulsed Nd-YAG laser (wavelength of 532 nm). A television camera (NTSC standard), combined with the pulsed laser, makes it possible to measure the transient motion of the tape. The pulse repetition rate of the laser is 30 pps, such that the speckle pattern of the tapes surface can be observed and recorded at intervals of 1/30 of a second and stored in frame memories. Isothetic fringes for in-plane displacement are obtained by computing the difference between the initial and succesive images. These isothetic fringes are processed automatically to obtain the values of the displacement by using digital techniques. By this method, the transient behavior of the tape can be analyzed. An example of the results is presented to show the dynamic motion of a tape traced by a revolving head at a speed of 5.77 m/s in a VTR.