Nanodisplacement measurements by frequency-modulated laser autodyne

Abstract

Background and Objectives: Measurements of nanodisplacements are relevant for various applications of self-mixing laser (autodyne), in particular when they are combined with microwave probe methods, which are sensitive not only to the profile, but also to the inhomogeneities of the material and the its internal structure. A laser autodyne method for measuring the nanodisplacement by triangular frequency modulation of the laser radiation is proposed. Materials and Methods: A computer simulation of the autodyne signal spectrum is carried out for the case of a change in the supply current of a laser diode according to the triangular law. The autodyne signal spectrum was measured using an RLD-650(5) laser diode on quantum-dimensional structures with a diffraction-limited single spatial mode. Results: The distances from the active medium of the laser autodyne to the reflecting surface are found, under which the conditions of equality of an integer number of half-waves to the length of the external resonator at both the lower and upper limits of the deviation range of the laser diode wavelength are satisfied. At these distances (equal-phase distances), the linear dependence of the amplitudes of the spectral components on the magnitude of the nanodisplacements of the surface is observed. This dependence was obtained by measuring the nanodisplacements of the Ratis XY piezo positioner, which is part of the NanoScan Technologies EG-3060 nano-pyezostation. Conclusion: The possibility of using an autodyne laser with frequency modulation of the radiation to control the nanodisplacements is shown. When the laser diode has a wavelength of 650 nm and the accuracy of measuring the amplitudes of the spectral components is 10%, the accuracy of measuring nanodisplacements can reach 10 nm.

Keywords

• self-mixing laser
• laser interferometry
• semiconductor laser
• frequency modulation
• nanoprophilometry
• spectral analysis
• measurement of nanodisplacements