The movies verify the advantages of the NFES and LRM methods for real-time plasmonic waveguide characterization with tunable wavelength and
excitation positions. With this system, the propagation properties of DLPPWs with different metallic films, dielectric coatings, and layouts were studied and compared. Results and discussion Propagation length of DLSPPW The properties of guiding broadband SPPs in DLSPPW with different metal films were studied by the setup. The dielectric strip was 200-nm wide and 300-nm high which coated on 100-nm-thick gold and silver films. DLSPPWs were excited directly by a white light source without the monochromator. Figure 2a,b shows the color CCD images of the leakage radiation of SPP mode on gold and silver films, respectively. In both cases, the propagation lengths of SPPs with red color were much longer than green and blue ones. The intensity of leakage radiation was proportional 4EGI-1 to the intensity in the waveguide. Therefore, we can measure the propagation loss directly from the images. The electric field of SPPs is written as E(z) = E 0 e iβx . The propagation length L defined by the distance of SPPs intensity decay to a factor of 1/e can be written as L = 1/2β ″, where the decay constant . The propagation length is dependent on the imaginary part of dielectric constant of materials and geometry selleck of the waveguide.
We obtain the L by fitting the measurement intensity by the equation I = I 0 + Ae -x/L . Figure 2c shows the RGB intensities as a AZD8931 clinical trial function of propagation distance. Compared with the propagation length in gold-based DLSPPW and silver-based one, the propagation length of the silver film was 1.25, 1.38, and 1.52 times longer than gold-based SPP at red, green, and blue color, respectively. The dielectric constants are -7.0124 + 0.2119i, -11.626 + 0.3634i, and -18.096 + 0.4842i for silver and -1.7562 + 5.2986i, -4.5461 + 2.4577i, and -11.548 + 1.2821i for gold at wavelengths of 450, 530, and 630 nm, respectively. These wavelengths are corresponding to the peak wavelengths
of RGB pixels in the CCD. It can be found that the imaginary parts of dielectric constants of silver are much smaller than those of gold. It indicates PI-1840 that silver has a longer propagation length than gold at the same wavelength. In addition, the propagation length of gold-based SPPs is increased from blue to red light because the imaginary part of dielectric constant is substantially decreased. Therefore, the ratio between the propagation lengths in silver- and gold-based waveguides is increased from red to blue light. The measured phenomenon is consistent with the wavelength-dependent dielectric constants of silver and gold. Figure 2 Leakage radiation images and intensity profiles of DLSPPW for gold-based and silver-based DLSPPWs. Leakage radiation images of SPPs on (a) gold film and (b) silver film. The bright spot is the excitation source from the fiber tip.