Fig. 1. (a) Schematic of plasmon oscillation for a nanosphere [1]. (b) Measured absorbance spectra of a GNR solution. The insets show the schematic of the transverse and longitudinal SPR modes, which correspond to two absorption peaks, respectively. (c) TEM images of as synthesized GNRs with different longitudinal SPR wavelength as noted [17]. (d) Measured absorbance spectra of gold nanospheres (GNSs) and GNRs, whose SEM images are shown in (c).

Fig. 2. (a) Schematic diagram of the GNR-based active nanosystem. (b) Calculated absorption cross section at the SPR wavelength of GNR as a function of gain coefficients (k). The spaser threshold is identified at k=0.0312. (c) Calculated scattering cross section spectra for the nanosystem with different k as noted. At the spaser threshold, the scattering cross section is enhanced by ∼7×104 times and the linewidth is compressed by two orders of magnitude. (d) Calculated absorption cross section at the SPR wavelength of GNS-based nanosystem as a function of k. The spaser threshold is identified at k=0.288. (e) Calculated wavelength-tunable spaser realized by varying the aspect ratio of the embedded GNR as noted [23].

Fig. 3. (a) Schematic diagram of the experimental setup based on a typical Kretschmann system [30,31]. (b) Measured amplified emission spectra of SPPs decoupled at θ=58.4°. Spectra were measured with different IP as noted (unit: mJ/cm2). The ASE peak is clearly identified at λASE=592.87  nm [31]. (c) Normalized emission spectra of SPPs decoupled at θ=59.2°, where the spectra are peaked at the ASE wavelength (λASE=592.87  nm). Inset: measured emission spectra of SPPs under different IP. With the increase of pump intensity, the ASE spectra are narrowed. (d) Angular distribution of SPP emission at wavelength 592.87 nm under different IP as noted. It can be seen that with the increase of pump intensity, the angular response is broadened unusually [32].

Fig. 4. (a)–(c) Pictures of three trapped polystyrene particles (2 μm in diameter) and their focused images in three dimensions. (d) Eight pictures of the trapped particles. The index number of each trap is indicated aside the trapped particle [41].

Fig. 5. Schematic diagram of the dual optical tweezers system [43].

Fig. 6. DF images of trapping and transferring of GNRs with dual optical tweezers in water solution. The Trap B was moved top-down from (a) to (d) and bottom-up from (d) to (g).

Fig. 7. Microscope images of positioning and patterning of gold nanoparticles. (a) Gray scaled picture of the patterned GNRs by optical trap on the bottom of the chamber. (b) Color picture of the patterned gold nanoparticles after the sample was dried [43]. The red “IOP” was “written” by GNRs first and the green “CAS” was “written” by GNSs subsequently on the same substrate.

Fig. 8. SEM pictures of fixed single and complex GNRs and their scattering spectra [43]. (a) is the SEM picture of a fixed single GNR, (b) is the measured scattering spectrum of the fixed GNR after the sample was dried, (c) is the calculated scattering spectrum of a single GNR whose shape is shown in the upper right corner. (d)–(f) and (g)–(i) are the SEM pictures of two couples of the fixed GNRs, the measured scattering spectra and the calculated scattering spectra of the coupled GNRs.

Fig. 9. (a) Schematic diagram of the optical trapping setup with cylindrical vector beams. The trapping laser was introduced into the polarized beam converter after expanding and focused to form a trap. (b) The experimentally generated radially and azimuthally polarized beams. The first column shows the isotropic intensity profiles of the vector beams imaged by a laser beam analyzer without a polarization analyzer. The next two columns show the intensity cross sections after inserting the polarization filter, with the arrows denoting the polarization direction [47].

Fig. 10. (a) Power spectra of gold spheres with a diameter of 90 nm trapped by radially polarized, azimuthally polarized, and Gaussian beams measured by analyzing the Brownian motion of the particles. The stiffness in the figure is normalized by laser power. (b) Transverse trapping stiffness as a function of laser power for 90 nm gold particles trapped by radially and azimuthally polarized beams, respectively [47].

Fig. 11. (a) Camera picture of three GNRs/PVA films in Petri dish. (b) Schematic diagram of the film stretch process [17].

Fig. 12. (a) Optical microscope images of the original and stretched film under white light illumination with polarization parallel (∥) and perpendicular (⊥) to the stretch direction. (b) Measured absorbance spectra of the GNRs/PVA films corresponding to (a). (c) TEM images of the aligned GNRs in the PVA film. Scale bar: 100 nm. Dashed lines indicate the direction of stretch. (d) Measured absorbance spectra of another stretched GNRs/PVA film under excitation polarized parallel (∥) and perpendicular (⊥) to the stretch direction. Solid lines are the corresponding calculations of a single GNR. (e) Polar plot of the measured absorption intensity at wavelength 800 nm versus the excitation polarization angle. The solid curve is a fit to the cosine squared function [17].

Fig. 13. (a), (b) Measured transmission of (a) original and (b) stretched GNRs/PVA films upon laser excitation polarized parallel (∥) and perpendicular (⊥) to the stretch direction, respectively. GNR concentrations (CGNR) of the films: (a) 3.75  nmol/L and (b) 15  nmol/L. (c) Normalized transmission of a stretched GNRs/PVA film excited with different laser intensities. The laser polarization was along the stretch direction. Solid lines are corresponding fittings with the Z-scan theory. (d) NLA coefficient (−β) as a function of the laser intensity for three samples: (open square) S1: original film with CGNR=3.75  nmol/L; (open triangle) S2: stretched film with CGNR=3.75  nmol/L; (open circle) S3: stretched film with CGNR=15  nmol/L. The experimental data and their fittings (solid lines) were multiplied by corresponding numbers as noted for comparison purpose [17].

Fig. 14. (a)–(d) Typical SEM images of HGNRs in original (a) and stretched (b)–(d) PVA films. Inset: SEM image of a single core-shell GNR hybrid nanostructure (HGNR). The GNR in the core is ∼95  nm in length and ∼45  nm in diameter. After the stretch, most of the HGNRs in the film are aligned with long axis along the stretching direction (indicated by dash lines). Scale bars are 500 nm. (e) and (f) Measured extinction spectra of (e) original and (f) stretched film under incident light polarization parallel (0°) and perpendicular (90°) to the stretching direction [49].

Fig. 15. (a) Measured emission intensity at wavelength 742 nm versus detection polarization angle (αdet) under excitation with circular polarization for the original and stretched film. The data are fitted with a cosine squared function together with an exponential decay. (b) Polar plot of the experimental and fitted data in (c) after calibrating the exponential decays. (c) Illustration of the applications of the stretched HGNRs for converting circularly polarized light into broadband linearly polarized emission [49].

Fig. 16. (a) Schematic setup for emission measurements with different angles of detection polarization (αdet) under certain excitation polarization angles (θex). (b) Measured emission spectra of the stretched film with different θex and αdet as noted. The symbols “∥” and “⊥” denote the angles of 0° and 90°, respectively. The first and second subscripts represent the values of θex and αdet, respectively. (c) Relative excitation emission efficiency of the emission spectra shown in (b). Spectra are normalized to the spectrum of I⊥ ∥. (d) Measured emission intensity at 742 nm versus αdet under excitation with θex=0°, 45°, 67.5°, and 90°, respectively [49].