5.1 Conclusions
A novel and simple method for measuring a small wavelength shift is proposed. The theoretical results showed that the sensitivity and resolution are superior to 5 deg/nm and 0.006 nm, respectively, can be achieved in a dynamic range of 2 nm (632-634 nm), and are superior to 3.1 deg/nm and 0.0095 nm in the range of 5 nm (632-637 nm).
The HSA TIR heterodyne interferometer is designed for measuring small angles. It can achieve the adjustable sensitivity by adjusting the β value. The measuring small angles interferometer by using the heterodyne interferometry and light reflection from (1 0 0) SW or SIS are proposed. Based on the derived phase-difference equations and measurement, the phase difference was applied to decide the small angle variation.
According to the experimental results and the theoretical analyses, the (1 0 0) SW interferometer can yield an angular resolution and sensitivity superior to 2×10−4 deg (3.5×10−6 rad) and 150 (deg∕ deg) at a measurable range of 0.45 deg. The SIS interferometer can achieve the adjustable sensitivity which is corresponding to the incident angle. They yield stable benefit based on the advantages of common-path [25, 39, 40] and heterodyne interferometry. The proposed hexagonal mirror architecture can be used to measure small-angle variations. Through observation of the light intensity variations, the angle variations can be determined. The design could be applied to detect the reference light intensity to eliminate factors causing by laser intensity variations which would affect the precision of measurements. The proposed structure is highly stable, low-cost, and easy to assemble. Based on these advantages, it can be effectively used to measure small-angle variations. The angle resolution and sensitivity of the architecture is 7.7×10-5 deg and 13000 μW/ deg, within a range of 0.25 deg.
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5.2 Future Prospects
Highly sensitive heterodyne interferometer and multi-layered film (glass-SF11, immersion oil, and silicon wafer: SIS) heterodyne interferometer system achieved the advantage of adjustable sensitivity. They also can be used in the measurement of fluid refractive index change (fig. 39). They may be able to use in biomedical sensing (fig.
40). They are already in the development process and possible to realize in the future.
Figure 39 Measurement of fluid refractive index using highly sensitive heterodyne interferometer system
Figure 40 Biomolecular sensor
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