INVESTIGATION OF THE METHOD OF DIRECT LASER WRITING OF OPTICAL ELEMENTS WITH BINARY HIGH-CONTRAST AMPLITUDE-PHASE TRANSMISSION

A method is proposed for formation on one substrate of two superimposed optical structures - a binary phase structure and an analog high-contrast amplitude structure made on a thick chromium film in the form of a regular two-dimensional zero-order diffraction grating with a variable fill-factor of cells. A numerical and experimental study of this method is carried out as applied to an optical transparency for generating the structure of a gamma-coupled laser beam. The quality of a high-contrast structure, suitable for practical application, was experimentally achieved, with an optical density of a chromium film of about 4.3, when measured at a wavelength of 532 nm, and with a minimum size of transparent and opaque windows of the order of 1x1 μm. This method can be used to synthesize amplitude-phase transparencies with a large alternating range of change in the amplitude optical transmittance, with a relatively slow (smooth) change in the transmittance (with the carrier spatial frequency of the amplitude modulation determined by the period of the above two-dimensional zero-order diffraction grating).

Improved spectral resolution of the femtosecond stimulated Raman spectroscopy achieved by the use of the 2nd-order diffraction method

Prolongation of the picosecond Raman pump laser pulse in the femtosecond stimulated Raman spectroscopy (FSRS) setup is essential for achieving the high spectral resolution of the time-resolved vibrational Raman spectra. In this work, the 2nd-order diffraction has been firstly employed in the double-pass grating filter technique for realizing the FSRS setup with the sub-5 cm−1 spectral resolution. It has been experimentally demonstrated that our new FSRS setup gives rise to a highly-resolved Raman spectrum of the excited trans-stilbene, which is much improved from those reported in the literatures. The spectral resolution of the present FSRS system has been estimated to be the lowest value ever reported to date, giving Δν = 2.5 cm−1.