抄録
Offer Organization: Japan Society for the Promotion of Science, System Name: Grants-in-Aid for Scientific Research, Category: Grant-in-Aid for Scientific Research (B), Fund Type: -, Overall Grant Amount: - (direct: 14900000, indirect: 1710000)
In our previous report, the optical frequency comb generator consisting of two phase modulators in tandem we used generated the narrow bandwidth of the comb spectrum, only 2 nm, and resulted in the limited resolution up to 300μm. And some noises of many side-lobes appeared around the interferometric peaks due to a rectangular frequency comb spectrum. Furthermore, it took a long time for the data acquisition because the point-to-point scanning was used in a fiber-optic interferometer.
To improve the performance of our previous system, we introduced new functions of a broad band frequency comb and a line-type image sensor to realize a frequency comb-based interferometric microscope. One of the improvements in the proposed system is that a broadband frequency comb spectrum of over 10 nm was obtained by combining a waveguide type-frequency comb generator^<6-8)> consisting of the phase modulator installed in the Fabry-Perot cavity and a subsequent wavelength equalizer^<9)>. The depth resolution is finally improved up to 35 μm, and the side-lobes in the interferometric signals also disappeared. Another important improvement is to realize a high-speed observation of three-dimensional images by the use of a line type-image sensor for capturing a line image in a horizontal direction at a time.
The measurement resolution narrowed finally to 35 μm by introducing the waveguide-type frequency comb generator and the wavelength equalizer. Furthermore, introducing the line image sensor can obtain the simultaneous measurement of the whole horizontal cross sectional image of the interferometric signal. We successfully demonstrated the 3 dimensional surface profilometry of a Japanese 10-yen coin and observation of a cross sectional tomography image of transparent thin films by varying the comb frequency interval without mechanical shift. The dynamic range in the depth direction was about 1.1 mm and the measurement resolution was 35μm. The standard deviation of seven times thickness measurements was 5μm.