Upon reflection from the interface of two media, the light beam experiences two optical shifts: a longitudinal shift in the plane of incidence and a transverse shift normal to the plane, often referred to as Goos-Hänchen (GH) shift and Imbert-Fedorov (IF) shift . Simultaneously, the reflected light beam also experiences a small in-plane and out-of-plane angular deviation from the prediction of Snell’s law, i.e., the angular GH and IF shift, respectively. GH and IF shifts have attracted much attention in recent years due to their potential applications in many aspects, such as optical waveguide switch, integrated optics, and optical sensors. The GH and IF shifts have been widely investigated in various media and optical structures, such as dielectric slabs, metal surfaces, photonic crystal, and metasurfaces. The temperature-dependent GH shift has been investigated theoretically and experimentally, and proposed to detect the temperature variations. However, to the best of our knowledge, only the spatial GH shift was included in the reported temperature sensors based on GH shift, whereas the angular GH effect was neglected. In addition, IF shift based temperature sensor has not been addressed yet. In this work, we theoretically investigate the temperature-dependent spatial and angular GH and IF shifts of reflected light beam from the interface of air/gold film, and demonstrate a temperature sensor based on the GH (IF) shift.
The spatial GH shift for the s-polarized light with a wavelength of 633 nm is negative, while the p-polarized light exhibits a positive spatial GH shift with a significantly larger amplitude. The s-polarized light possesses a negative angular GH shift with its amplitude increases with the incident angle. For the p-polarized light, it exhibits positive and negative angular GH shifts, which depends on the incident angle. The s-polarized light exhibits a positive spatial IF shift. For the angular IF shift, it is negative for the s-polarized light, whereas the p-polarized light possesses a positive angular IF shift. The spatial and angular shift of the reflected beam can be combined into a total beam displacement when observed with a distance from the origin. For temperature sensing applications, the total beam displacement of the GH (IF) effect between the p- and s-polarized incident light was monitored. It is found that both the GH and IF shift based temperature sensor exhibit positive and negative sensitivities. The maximum sensitivity (amplitude) for the GH shift temperature sensor was obtained from 633 nm light beam incident onto the surface of gold film at almost grazing incidence (e.g., 0.3631 nm/K with the incident angle of 89 degrees). In contrast, a much smaller sensitivity of 0.01615 nm/K was obtained for temperature sensor based on the spatial GH shift. The maximum sensitivity is 0.09477 nm/K for the IF shift based temperature sensor, much smaller than that based on the GH shift. The sensitivity of the temperature sensor also depends on the wavelength of incident light. The maximum sensitivity for the GH shift temperature sensor increases with the wavelength, and the sensitivity of 6.337 nm/K was achieved using 3000 nm light at the almost grazing incidence. For the IF shift temperature sensor, the maximum sensitivity decreases with the wavelength of incident light. The findings will open up new opportunities for the development of GH and IF shift based highly sensitive optical thermometry.
The charge carrier mobility is an important parameter to characterize the performance of organic semiconductors based optoelectronic devices. In a given organic semiconductor, the mobility is often calculated based on the space-charge-limited (SCL) current measurement by fitting the corresponding current-voltage (J-V) data with a range of available space-charge-limited transport models to achieve the best fit, however, the accuracy of extracted mobility parameter relies on the correctness of model being used. Here, we present a fractional-dimensional SCL transport model for organic semiconductors with spatial disorder based on the fractional-dimensional calculus approach. We show that the thickness scaling of the SCL current is related to the spatial disorder in organic devices. The fractional-dimensional SCL transport model agrees well with the measured current density of several organic diode devices. The reported model is able to extract mobility values in organic devices with better accuracy as compared to existing models in the literature.
A new D-type fiber optic sensor based on silicon/graphene hybrid structure is proposed. The refractive index variations are detected with phase difference changes instead of the conventional intensity and spectral variations. An ultrahigh phase sensitivity of 1:3716×10<sup>6</sup> deg=RIU (RIU: refractive index unit) was achieved, which is 3447- fold and 380-fold higher than that of fiber optic sensor without silicon/graphene coating, and with only silicon coating, respectively. This phase sensitivity enhancement factor is depending on the incident angle. The phase sensitivity decreases with the incident angle, height of fiber core, while increases with the length of sensing region.
In this paper, we present a model to account for the absorption of ultrafast laser pulse on a metallic tip and to calculate its induced hot carriers (or electrons) emitted from the surface over a wide range of operating condition from low (multiphoton absorption) to high (optical tunneling) laser field. The model self-consistently include the non-equilibrium heating of the electrons with time-dependent electron energy distribution and multiple-energy time-dependent tunneling process. A universal critical Keldysh parameter at the transition between the multiphoton absorption and optical tunneling regimes is obtained. The effect of the plasmonic enhancement at the tip at sub-10 fs laser pulses are also studied. It is found that at very short laser pulse (a few cycles), the classical photo-electric effect is not valid. For the plasmonic effect, there is a time delay between the plasmonic field and laser field, and thus the emission of electrons are lapsed than the laser field. The enhancement of electron emission due to the ultrafast laser induced plasmonic field at low field regime is also discussed.