간섭계를 이용한 나노 계단 형상 측정 및 레이저 안정화

Abstract

In this thesis, we introduced two experiments. One is height measurement of reference step with 93.1 nm thickness by using stabilized interferometer and FFT method, another one is laser stabilization and hyperfine structure measurement by using tilt locking method. The PID controller was employed in two experiments for stabilization system. In order to measure the height measurement of reference, we developed a program in mathcad software. First we simulated FFT in 1D and 2D profile to check whether our generated mathcad codes are correct or not by using Tekeda and Kreis method. Before we did the simulation, we had introduced some basic knowledge about FFT and compared FFT with phase shift method. Then we used FFT method to measure the reference step height with thickness 93 nm in the highly windy environmental conditions. After obtaining the value of the reference step height, we compared it with the measurement in vibrationless conditions with commercial Mirau type interferometer using Accura2000 system. Except above contents, we also introduced some basic knowledge and procedure of tuning the parameters of PID controller so as to get the stabilization of Twyman-Green interferometer. As the result, the reference step height with the thickness (93.1±1.2 nm) has been measured. In another case, we introduced how to stabilize the frequency of diode laser using tilt locking technique. First we introduced the historical background of tilt locking method and drew the comparison between it with other traditional methods. We set up a Sagnac interferometer to create an error due to phase shift. Phase shift is derived from the changing of refractive index of atom. In order to demonstrate the principle clearly, the first two Hermite-Gauss modes TEM00 and TEM01 are introduced. The hyperfine manifolds [5²S_((1)/(2)) F3→F’=2, 3, 4, 5²P_((3)/(2))^(85)Rb] is obtained using the error signal finally. The PID controller is employed in the experiment with the Sagnac interferometer together to make up of the servo loop and get the modulation-free frequency locking of a diode laser. As the result, the laser frequency is stabilized up to sub-megahertz lev`el in the experiment.