Fig. 4
From: Non-fluorescent nanoscopic monitoring of a single trapped nanoparticle via nonlinear point sources
Experimental setup and monitoring of second-harmonic signals. a Two-laser scheme for simultaneous trapping and monitoring. A femtosecond (fs) pulse laser and a continuous-wave (CW) laser are independently used for monitoring and trapping, respectively. The two lasers are combined with a 50:50 coupler and the short wavelengths of the laser beam are filtered with a long-pass filter (LPF). The transmitted fundamental wave signal (Iω) is monitored by an infrared photodetector, and the short-wavelength second-harmonic (SH) signal (I2ω) filtered by a short-pass filter (SPF) and a band-pass filter (BPF) is monitored by an electron multiplying charge-coupled device (EMCCD) and a photomultiplier tube (PMT). b–d Time traces of SH intensities (I2ω) with different fs-laser powers (Pfs = 4.0, 5.5, and 7.5 mW) in the absence of the CW trapping laser. When Pfs = 4.0 mW, a stable nonlinear monitoring signal is observed
