Fig. 1. Principle of holographic optical tweezers. (a) Sketch of the holographic optical tweezers setup (QWP: quater-wave plate;NPBS: non-polarizing beam splitter); (b) and (c) the working mode of an SLM: (b) normal incidence and (c) small-angle incidence

Fig. 2. The principle of holographic beam shaping based on Fourier transform

Fig. 3. The trap patterns obtained with the six common CGH algorithms

Fig. 4. Flow charts of algorithms. (a) FFT-GS algorithm; (b) GAA algorithm

Fig. 5. Optical field calculation based on the GS iterative algorithm. (a) The target optical field; (b) the theoretically reconstructedoptical field; (c) the standard error between the theoretically reconstructed optical field and the target optical field against the iterations

Fig. 6. Regulating the cell polarization and growth using optical tweezers^[61]. (a1)-(a4) Controlling the polarization of migration direction using optical tweezers carrying chemoattractants: (a1) the particle carrying fMLP moved close to HL-60 cell; (a2) the cell was polarized and migrated to the particle; (a3) and (a4) the polarization and migration directions of the cell were changed when the particle was rotated anticlockwise around the cell. (b1)-(b

Fig. 7. Stretching the red blood cell with holographic optical tweezers and measuring its phase distribution^[65]. (a) Schematic of the optical traps configuration for symmetrical deformation; (b) the wide-field images and the reconstructed phase maps based on DHM; (c) the diameter of the RBC changes over time in the vertical and horizontal directions

Fig. 8. Principle of measuring the elastic modulus of the DNA molecule using optical tweezers^[70]. (a) The geometry based on single-trap optical tweezers and the DNA molecule attached to some surface; (b) the geometry based on single-trap optical tweezers and the DNA molecule attached to one microtube; (c) the geometry based on two traps optical tweezers

Fig. 9. Stretching the DNA molecule with holographic optical tweezers^[72]. (a) The stretching process; (b) the change of position of the two microspheres in the x-direction; (c) the change of position of the two microspheres in the y-direction; (d) the force-extend curve before the microsphere was labeled; (e) the force-extend curve after the microsphere was labeled

Fig. 10. Combination of holographic optical tweezers and super-resolution microscopy ^[79]. (a) Horizontal alignment of the E-coli cell with holographic optical tweezers; (b) the super-resolved image of the horizontally aligned cell; (c) vertical alignment of the E-coli cell with holographic optical tweezers; (d) the super-resolved image of the vertically aligned cell; (e) the one-dimensional intensity plot along the blue line marked in figur

Fig. 11. Measuring the three-dimensional refractive index based on holographic optical rotation of yeast cell^[85]. (a) The interference pattern when the yeast cell is rotated to the position of 0°; (b) the interference pattern when the yeast cell is rotated to the position of 45°; (c) the interference pattern when the yeast cell is rotated to the position of 90°; (d) the interference pattern when the yeast cell is rotated to the position of 135°; (e) the