Philip H. Jones, Onofrio M. Maragò & Giovanni Volpe
Fig. 1.2 — Basic experimental design
Optical tweezers are generated by focusing a laser beam to a diffraction-limited spot using a high-numerical-aperture objective lens (OBJ). Additional optics is needed to steer the optical tweezers position (beam-steering mirror M2 and telescope formed by lenses L1 and L2), to image the sample (lamp, dichroic mirrors DM1 and DM2, camera lens L3 and camera) and to track its position (condenser C, lens L4 and quadrant photodiode QPD). The Brownian motion of the trapped particle can be tracked either by digital video microscopy or by interferometry and the measured particle trajectory can be used to calibrate the optical tweezers stiffness.