Der-Chin Su

Complex refractive-index measurement based on Fresnel’s equations and the uses of heterodyne interferometry

The phase difference between s and p polarization of the light reflected from a material is used for measuring the materials complex refractive index. First, two phase differences that correspond to two different incidence angles are measured by heterodyne interferometry. Then these two phase differences are substituted into Fresnels equations, and a set of simultaneous equations is obtained. Finally, the equations are solved by use of a personal computer by a numerical analysis technique, and the complex refractive index of the material can be estimated.

Refractive-index measurement based on the effects of total internal reflection and the uses of heterodyne interferometry

A new method for measuring the refractive index is presented. First, the phase difference between s and p polarizations that is due to the total internal reflection is measured by heterodyne interferometry. Then, substituting this phase difference into the Fresnel equations, we can obtain the refractive index of the test medium.

Method for measuring the retardation of a wave plate

An electro-optic modulator applied to a carrier frequency is used to measure the retardation of a wave plate. This method is not only suitable for any wave plate but also can be operated in real time.

Angle measurement using total-internal-reflection heterodyne interferometry

A new optical method for angle measurement based on total- internal-reflection heterodyne interferometry is presented. In this method, heterodyne interferometry is applied to measure the phase dif- ference between s and p polarization states at total internal reflection. This phase difference depends on the angle of incidence. Hence, small- angle measurement can be performed only by evaluating this phase difference. The validity of the method is demonstrated, and it has a mea- surement range of 10 deg. Its resolution depends on the angle of inci- dence; the best resolution is 8310 25 deg.

An improved technique of measuring the focal length of a lens

Abstract Based on a Talbot interferometry, an improved technique for measuring the focal length of a lens is proposed. First, the test lens is positioned at the Talbot image of a grating, then a different grating is arranged at the Talbot image of the first grating through the test lens. This arrangement not only expands the measurable range, also improves the precision of the measurement. This technique is suitable for measuring both long and short focal length of a lens which can be concave and convex.

Measurement of wavelength shift by using surface plasmon resonance heterodyne interferometry

A linearly polarized light is incident on a surface plasmon resonance (SPR) apparatus at the resonant angle, the surface plasmons are excited. Small wavelength shifts will introduce phase difference variations between s- and p-polarizations of the reflected light. These phase difference variations can be measured accurately by using heterodyne interferometry. Based on these facts, a novel method for measuring small wavelength shifts is proposed. It has the advantages of both common-path interferometry and heterodyne interferometry.

Improved technique for measuring small angles

Based on the total-internal-reflection effect and heterodyne interferometry, an improved technique for measuring small angles is proposed. This technique not only expands the measurement range but it also improves measurement performances. Its validity is demonstrated.

A new technique for measuring the affective focal length of a thick lens or a compound lens

Abstract A new technique, based on the Talbot interferometry and ray tracing, for measuring the affective focal length of a thick lens or a compound lens is proposed. A test lens is positioned between two gratings. First, we adjust the position of the first grating, and take a high contrast moire pattern. Then we displace the second grating far from the test lens with a known distance. We readjust the position of the first grating and take another high contrast moire pattern. From the tilt angles of these two moire patterns and the displaced distance of the second grating, we can evaluate the effective focal length of the test lens.

Interferometric optical sensor for measuring glucose concentration

With a specially designed probe, the phase difference between s andp polarization of light reflected under surface-plasmon resonance is measured by use of a common-path heterodyne interferometer. For specific ratios of phase difference to glucose concentration, the glucose concentration can be estimated as a function of the measured phase data. A prototype was set up to demonstrate the feasibility of this sensor, which was experimentally tested in the range 40-500 mg/dl with a small quantity of solution and had a measurement resolution of 1.41 mg/dl at 25 degrees C.

Method for determining the optical axis and n e ,n o of a birefringent crystal

There is a phase difference between s and p polarizations when a circularly polarized heterodyne light beam is reflected from a birefringent crystal. It can be measured accurately with a common-path heterodyne interferometric technique. We have derived an equation that describes the relationship between the phase differences and n(e), n(o), and alpha. Two groups of solutions for (n(e), n(o)) can be obtained from this equation by the phase measurements performed at three incident angles under moderate conditions. Each group consists of three pairs of solutions for (ne), n(o)). Finally, by justifying with physical conditions, we obtained the correct solution for (n(e), n(o)). Azimuth angle alpha of the birefringent crystal optical axis can also be determined. And the feasibility of this method is demonstrated.