Direct Observation of a Transition of a Surface Plasmon Resonance from a Photonic Crystal Effect

Transition of surface-plasmon resonance from out-of-plane photonic crystal effect is observed in a semiconductor array of subwavelength holes by optical pump-terahertz probe measurements. The dielectric properties of the photoexcited array are essentially altered by the intense optical excitation due to photogenerated free carriers. As a result, the array becomes metallic and favors the coupling and propagation of surface plasmons. The photoinduced resonant extremes agree well with the Fano model.

Figure 1

(a) Measured transmitted terahertz pulses and (b) the corresponding Fourier-transformed spectra through air reference, blank Si, Si array of perpendicular, and parallel orientations with (black curves) and without (gray curves) optical excitation at an 111 mW average power. The inset shows the scanning electron microscopic image of the Si array of elliptical through holes.

Figure 2

Measured (dots) and the Fano profiles (solid curves) of frequency-dependent terahertz transmission through the Si array in both perpendicular and parallel orientations under 111 mW optical excitation. The vertical dashed lines represent the resonance peaks. The fitting parameters are $q_v=12.59\pm 0.2$, ${\omega }_v/2\pi =1.46\pm 0.05\mathrm{THz}$, ${\Gamma }_v/2\pi =0.43\pm 0.05\mathrm{THz}$, and $T_b=(2.7\pm 0.1)\times {10}^{-3}$ for the $[\pm 1,0]$ mode; and $q_v=12.59\pm 0.2$, ${\omega }_v/2\pi =1.81\pm 0.05\mathrm{THz}$, ${\Gamma }_v/2\pi =0.45\pm 0.05\mathrm{THz}$, and $T_b=(0.8\pm 0.1)\times {10}^{-3}$ for the $[0,\pm 1]$ mode.

Figure 3

Measured dielectric constant of photoexcited Si at 1.50 THz as a function of optical excitation. The real (${\epsilon }_{r2}$) and imaginary (${\epsilon }_{i2}$) dielectric constants are represented by open circles and squares, respectively. The dotted curves are to guide the eye.

Figure 4

Frequency-dependent terahertz transmission through the array of perpendicular orientation under various laser excitations ranging from 0 to 111 mW. The measurements for different optical excitations are vertically shifted for clarity.

Figure 5

Measured resonance linewidth of the SP $[\pm 1,0]$ mode as a function of optical excitation power. The dotted curve is to guide the eye.