JPH0712545A - Interatomic-force-microscope detection apparatus by differential heterodyne interferometer using optical-fiber array - Google Patents

Abstract

PURPOSE:To enhance the visibility of the apparatus by a method wherein a cylindrical lens is used in the light-receiving system of a differential heterodyne interferometer using an optical-fiber array. CONSTITUTION:Output light from an optical-fiber array FA is changed into parallel light by a lens L1, the S component of polarized light is reflected via a half-wavelength plate HP and a polarized-beam splitter BS, and it becomes a reference signal via a cylindrical lens CL1 and a photodetector PD1. The P component of the polarized light is incident on a cantilever MC from a quarter-wavelength plate QP and a lens L2. Its reflected light is detected as a beat signal by a detector PD2 through the beam splitter BS and a cylindrical lens CL2, and the phase difference between the detectors PD1, PQ2 is detected by a phase meter. In addition, equal-inclination interference fringes by the inclination of two beams of radiant light from the array FA are magnified to several times by the cylindrical lens, they are incident on the photodetector through a slit, the visibility of the apparatus can be enhanced to about five times, the beat signal whose S/N ratio is good can be detected, and the displacement of the cantilever can be detected with good accuracy.

Description

DETAILED DESCRIPTION OF THE INVENTION In the conventional heterodyne interferometers, a two-point differential type optical system is configured by using a Wollaston prism using orthogonal two-frequency light sources. There is a problem that the relationship between the output and the measured phase becomes nonlinear due to the polarization leakage component. In the present invention, in order to detect the displacement of the cantilever of the atomic force microscope, an optical fiber array is manufactured using a polarization-maintaining optical fiber to construct a heterodyne interferometer. A schematic diagram of this device is shown in FIG. The two polarization-maintaining optical fibers are used to separately transmit the two frequency-shifted lights by the acousto-optic device so that there is no polarization leakage component. The directions of the electric vectors of the light output from the optical fiber array FA are the same. The lens L1 collimates the light. The direction of the electric vector is set to 45 degrees with respect to the optical axis of the polarization beam splitter BS through the half-wave plate HP. The S component of the polarized light is reflected, and the beat signal is detected on the photodetector PD1 through the cylindrical lens CL1. This becomes the reference signal. The P component of the polarized light enters the cantilever MC through the quarter wavelength plate QP lens L2. Regarding the focal point, one point is at the base of the cantilever and the other point is at the tip of the cantilever. The reflected light passes through the lens L2 and the quarter wave plate QP and is reflected by the polarization beam splitter. It is detected as a beat signal by the photodetector PD2 through the cylindrical lens CL2. The cantilever displacement information is included in the phase of this beat signal. The phase difference between the beat signals of PD1 and PD2 is detected by a phase meter. This phase difference is a phase difference corresponding to two points on the cantilever, and the phase of the common optical path such as the optical fiber is differentially canceled. This makes it possible to eliminate the effects of disturbances such as temperature changes in the optical fiber. With the cylindrical lens, the equi-tilt interference fringes formed by the tilts of the two outgoing lights from the optical fiber array are magnified several times and enter the photodetector through the slit. As a result, the visibility can be improved about 5 times, the beat signal with good S / N can be detected, and the displacement of the cantilever of the atomic force microscope can be accurately detected.

[Brief description of drawings]

Fig. 1 Schematic diagram of atomic force microscope detector by heterodyne interferometer using optical fiber array (description of symbols) FA optical fiber array E electric vector L1 lens F1 focal length of lens L1 HP 1/2 wavelength plate BS polarization Beam splitter QP Quarter wave plate L2 lens F2 Lens L2 focal length MC Cantilever HL Cantilever holder SPS Sample scanning unit CL1, CL2 Cylindrical lens PD1, PD2 Photodetector

Claims (1)

[Claims] Device with improved visibility by using a cylindrical lens in the light receiving system of a differential heterodyne interferometer using an optical fiber array