Direct measurement of the Goos-Hänchen shift using a scanning quadrant detector and a polarization maintaining fiber.
High precision measurements of optical beam shifts are important in various fields including sensing, atomic force microscopy, and measuring beam shifts at interfaces. Sub-micron shifts are generally measured by indirect techniques such as weak measurements. We demonstrate a straightforward and robust measurement scheme for the shift, based on a scanning quadrant photodiode (QPD) that is biased using a low noise electronic circuit. The shift is measured with respect to a reference beam that is co-propagating with the signal beam. Thus, the shift of the signal beam is readout directly as the difference between the x-intercepts of the QPD scan plot of the signal and reference beams versus the position of the detector. To measure the beam shift, we use polarization multiplexing scheme where the p-polarized signal and s-polarized reference beams are modulated at two different frequencies and co-launched into a polarization-maintaining fiber. Both the signal and reference beam positions are readout by two lock-in amplifiers simultaneously. In order to demonstrate the utility of this method, we perform a direct measurement of Goos-Hänchen shift of a beam that is reflected from a plane gold surface. Accuracy of 150 nm is achieved using this technique.
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India.
Venkata Jayasurya
VJ
Yallapragada
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India.
Gajendra L
GL
Mulay
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India.
Ch N
CN
Rao
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India.
Ajith P
AP
Ravishankar
Tata Institute of Fundamental Research, Homi Bhabha Road, Mumbai 400005, India.
Venu Gopal
VG
Achanta