Figure 12.3 — Concrete implementations of spectroscopic optical tweezers Figure 12.3 — Concrete implementations of spectroscopic optical tweezers. (a) Fluorescence optical tweezers. The near-infrared (850 nm) laser beam is used for optical trapping and the green (532 nm) laser beam for fluorescence excitation. A number of optical filters are used along the imaging path to isolate the fluorescence. (b) Two-beam photoluminescence optical tweezers. The 1064 nm laser beam (steerable in two dimensions by acousto-optic deflectors) is used for optical trapping and two-photon photoluminescence, and the 514.5 nm laser beam for direct absorption excitation. Spectra are recorded using a grating spectrometer with a CCD array. (c) Two-beam Raman optical tweezers set-up. The 1064 nm laser beam and the spatial light modulator are used to generate a set of steerable optical traps, whereas the 785 nm laser beam is used to excite the Raman signal.Figure (a) is reprinted with permission from van Dijk et al., J. Phys. Chem. B 108, 6479–84. Copyright (2004) American Chemical Society.Figure (b) is reprinted with permission from Wang et al., Nano Lett. 11, 4149–53. Copyright (2011) American Chemical Society.Figure (c) is reprinted from Creely et al., Opt. Express 13, 6105–10. Copyright (2005) The Optical Society.