しばらく忘れていたが色収差のないレンズの作り方を忘れていた。
このブログでも何度も取り上げていたのだが私は忘れっぽい。
色収差を気にしなければ太陽光の３色を集光できるはずだったのだ。
色収差があると焦点を結ぶ場所が位置がずれてしまって
うまく焦点が揃わないのだ。
色収差をなくすには
Focusing and imaging characterizations of the RGB-achromatic metalenses
Focusing and imaging characterizations of the RGB-achromatic metalenses
Figure 2A shows a scanning electron microscope image of the fabricated 2-mm-diameter metalens with NA = 0.7 (see section S4 for additional images). The metalens is composed of TiO2 nanofins of different geometries and rotation angles that are tailored for independent control of phases and dispersion. Figure 2B shows the measured focal intensity profile in the XZ plane of the metalens at the design wavelengths. The setup and measurement details are illustrated in section S3. The maximum focal shift among three focal spots at the RGB wavelengths is around 1 μm, which is ~0.1% of the design focal length. The error arises from fabrication imperfections. Figure 2 (C to E) shows the measured intensity distribution in the focal plane, and the corresponding Strehl ratios at the design wavelengths are all close to unity, as shown in Fig. 2 (F to H). Such nearly ideal focusing is the result of the combined effects of dispersion engineering and zone interference engineering. The RGB focusing of the metalens with NA = 0.3 is similarly achromatic and diffraction limited (section S3).
Fig. 2 Fabrication and characterizations of the RGB-achromatic metalens.
(A) A scanning electron microscopic image of the fabricated metalens with NA = 0.7. Scale bar, 1 μm. (B) Measured focal intensity distribution of the metalens in the XZ plane showing negligible focal shift (~0.1% of the focal length) at the design wavelengths. (Cto E) Measured focal intensity profiles in the focal planes. (F to H) Corresponding focusing intensity line profiles of (C) to (E). FWHM, full width at half maximum.