Ming-Hung Chiu

High-sensitivity small-angle sensor based on surface plasmon resonance technology and heterodyne interferometry

A high-sensitivity small-angle sensor based on surface plasmon resonance technology and heterodyne interferometry is proposed that uses a new technique with two right-angle prisms. Interestingly, the technique provides a novel method for designing small-angle sensors with high sensitivity and high resolution. Its theoretical resolution can reach 1.2x10(-7) rad over the measurement range of -0.15 degrees < or =theta< or =0.15 degrees . The method has some merits, e.g., a simple optical setup, easy operation, high resolution, high sensitivity, and rapid measurement. Its feasibility is demonstrated.

Small-displacement sensing system based on multiple total internal reflections in heterodyne interferometry

A small-displacement sensing system based on multiple total internal reflections in heterodyne interferometry is proposed. In this paper, a small displacement can be obtained only by measuring the variation in phase difference between s- and p-polarization states for the total internal reflection effect. In order to improve the sensitivity, we increase the number of total internal reflections by using a parallelogram prism. The theoretical resolution of the method is better than 0.417 nm. The method has some merits, e.g., high resolution, high sensitivity, and real-time measurement. Also, its feasibility is demonstrated.

Transmission-type angle deviation microscopy

We present a new microscopy technique that we call transmission angle deviation microscopy (TADM). It is based on common-path heterodyne interferometry and geometrical optics. An ultrahigh sensitivity surface plasmon resonance (SPR) angular sensor is used to expand dynamic measurement ranges and to improve the axial resolution in three-dimensional optical microscopy. When transmitted light is incident upon a specimen, the beam converges or diverges because of refractive and/or surface height variations. Advantages include high axial resolution (approximately 32 nm), nondestructive and noncontact measurement, and larger measurement ranges (+/- 80 microm) for a numerical aperture of 0.21 in a transparent measurement medium. The technique can be used without conductivity and pretreatment.

Small displacement measurements based on an angular-deviation amplifier and interferometric phase detection

We propose a method for small displacement measurement based on the angle deviation to phase change transformation. The phase change of common-path heterodyne interferometry due to the angle deviation of incidence of a light at interfaces caused by the displacement is detected by a lock-in amplifier. To obtain more accurate results we used an angular amplifier to increase the angle deviation and utilized a surface plasmon resonance (SPR) sensor to enhance the performance of phase detection. When a translator moves one of two face-to-face plane mirrors at an end and then rotates it a small angle, a light is incident onto the mirrors and reflected N times. The outgoing light is also deflected N times of the angle and incident into a SPR sensor. Thus the phase shift due to the angle deviation is amplified N times. The accumulated phase shift is proportional to the amplified angle deviation and displacement. Therefore, the phase change is obtained and the displacement is measured. The amount of movement required can be as low as 0.13 μm without an SPR sensor or 0.08 μm with an SPR sensor. The maximum measurement range can reach 1000 μm.

Phase geographical map for determining the material type of a right-angle prism

A phase geographical map for determining a right-angle prism is presented. The proposed method is based on total-internal-reflection effects and chromatic dispersion. Under the total-internal-reflection condition, the phase difference between the S and P polarizations, as a function of the wavelength and refractive index, can be extracted and measured using heterodyne interferometry. Various wavelengths correspond to various refractive index values. The proposed map is convenient in ensuring the prism material using a specific V number. The method has the following merits: high stability, ease of operation, and rapid measurement.

Lateral and axial resolutions of an angle-deviation microscope for different numerical apertures: experimental results

This paper presents a study of the lateral and axial resolutions of a transmission laser-scanning angle-deviation microscope (TADM) with different numerical aperture (NA) values. The TADM is based on geometric optics and surface plasmon resonance principles. The surface height is proportional to the phase difference between two marginal rays of the test beam, which is passed through the test medium. We used common-path heterodyne interferometry to measure the phase difference in real time, and used a personal computer to calculate and plot the surface profile. The experimental results showed that the best lateral and axial resolutions for NA = 0.41 were 0.5 μm and 3 nm, respectively, and the lateral resolution breaks through the diffraction limits.

Transmission-type angle deviation microscope with NA=0.65 for 3D measurement

Transmission-type laser scanning angle deviation microscopy (TADM) with NA=0.65 for three dimension (3D) measurement is presented. It is based on the theorems of geometrical angular deviation and surface plasmon resonance (SPR) and the use of the common-path heterodyne interferometry. When a laser beam defocuses on the surface of a transparent sample, the transmission light will be deviated a small angle from the optical axis and the deviation angle is proportional to the defocus length and the square of the numerical aperture. We used a SPR angular sensor and the common-path heterodyne interferometry to measure this deviation angle. Scanning the sample, the phase profile was measured and transferred to surface height pattern, the 3D surface profile was obtained in real-time. The results showed that the dynamic range and lateral and axial resolutions were equal to ±5.6 μm, 0.3 μm, and 3 nm, respectively.