Fig. 1. (a) Experimental setup: the light source is a He-Ne laser at 632.8 nm (Thorlabs HNL210L); HWP, half-wave plate for attenuating the light intensity; L1, short-focus lens (variable); P1 and P2, Glan polarizers; prism with refractive index n=1.515 (at 632.8 nm); L2, long-focus lens (150 mm); CCD, Coherent LaserCam HR. Dotted box: the schematic of the standard lock-in technology. PolM, polarization modulator; PSD, position sensitive detector; their frequencies keep synchronous. (b) and (c) denote the focused beam waist at different positions relative to the reflection surface.

Fig. 2. ∂ΔH/∂ω0 (the sensitivity of the amplified shift to the beam waist) varies with incident and postselection angles. The extreme values are indicated by the black dashed lines.

Fig. 3. Amplified shift changing with the postselection angle and the beam waist. Here, the beam waist is chosen as 15.96, 19.09, and 20.81 μm. The incident angle is 65°. The squares, circles, and triangles denote the experiment data corresponding to different beam waists. The curves are theoretical predictions from Eq. (7).