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The conductivity of a monolayer graphene at intraband transitions is sensitive on the Fermi level and on the wavelength of the incident beam. Changing conductivity values through these parameters thus may offer better control of light impinging on graphene. In this paper, we investigate reflection, the simplest interaction of light on such surface, by looking at the Goos-Hanchen (GH) shift experienced by the incident light where the wavelength is at terahertz range. With this wavelength range, we assume that the carriers in graphene undergo intraband transition. We calculate that spatial and angular GH shifts can be present. For both GH shifts in general, we find that increasing the Fermi level changes the incident angle at which the maximum GH shifts arise. Moreover, we see that at higher frequencies, the amount of beam shift decreases with the Fermi level. At lower frequencies on the other hand, the shift becomes proportional to the Fermi level. Upon obtaining the measurable shifts, we find that the magnitude of the physical shifts can be easily detected given appropriate experimental parameters. Our results may increase the utility of graphene in optoelectronics devices and applications.

The orbital angular momentum (OAM) of light has become a central topic in quantum information and optical communication. In applications OAM is typically probed by observing a beam's diffraction through binary amplitude and phase masks. Distinguishing the different OAM states of the beam is usually difficult, though, so here the authors program a digital micromirror array to shift the setup's slit transversely, to exploit the unique phase of an OAM beam. By observing how diffraction varies as the slit changes, one can probe higher OAM values than usual, allowing access to theoretically unlimited OAM states for high-dimensional quantum systems, or for multiplexing in communication.

The orbital angular momentum (OAM) of light are central to different areas of research because they can provide theoretically infinite allowable states. Here, use a movable slit to probe the OAM of Lagguerre-Gaussian beams.

Four-lens paraxial cloak theory is extended to accommodate lenses with different focal lengths. Solutions of this case were found and cloaking was still observed in experiments, with only small background magnification.

Quadrant detectors (QD) are mainly used in research and industries for displacement measurement purposes due to their high sensitivity and accuracy as compared to other photodiode devices. Their scope extend to sub-nanometer scales and they are also operable at a wide temperature range with fast response frequencies, which make them the best candidate for beam displacement measurements. A growing interest in the field of optics are beams carrying orbital angular momentum (OAM), particularly Laguerre-Gaussian (LG) beams, due to their remarkable applications, which include optical tracking and gravitational wave detection. This study shows the combined effect of using different OAM modes of LG beam and varying angles of inclination of the QD on the sensitivity response and linearity index of the QD. In general, it was observed that a lower OAM value for the LG beam gives a higher sensitivity for the QD and a higher angle of inclination for the QD leads to a higher linearity index. This result gives a larger range of application for the QD.

We demonstrate cloaking with four lenses of different focal lengths. To achieve this, we compute the separation distances between lenses such that the effective ABCD matrix is equal to just a propagation in free space. Previously, calculations using this method are restricted to 2 pairs of lenses with equal focal lengths. Our computations, on the other hand, had no such restrictions: we generalize even with an asymmetric case. We derive expressions that show the dependence of the distances on the lenses and their focal lengths. Furthermore, we propose a way to minimize the length of this cloak. Our equations reduce to the Rochester cloak when its restriction is imposed. A general paraxial cloak could be useful in advanced undergraduate experiments in optics because: 1) the limit imposed by the focal length has been lifted; and 2) there is a pedagogical benefit of doing experiments with lenses beyond the usual imaging experiments such as reinforcing concepts in Gaussian optics., Comment: 10 pages, 4 figures

That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s group velocity vg. Here, we report the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement. Our results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space.

Coherent frequency conversion of structured light, i.e. the ability to manipulate the carrier frequency of a wave front without distorting its spatial phase and intensity profile, provides the opportunity for numerous novel applications in photonic technology and fundamental science. In particular, frequency conversion of spatial modes carrying orbital angular momentum can be exploited in sub-wavelength resolution nano-optics and coherent imaging at a wavelength different from that used to illuminate an object. Moreover, coherent frequency conversion will be crucial for interfacing information stored in the high-dimensional spatial structure of single and entangled photons with various constituents of quantum networks. In this work, we demonstrate frequency conversion of structured light from the near infrared (803 nm) to the visible (527 nm). The conversion scheme is based on sum-frequency generation in a periodically poled lithium niobate crystal pumped with a 1540-nm Gaussian beam. We observe frequency-converted fields that exhibit a high degree of similarity with the input field and verify the coherence of the frequency-conversion process via mode projection measurements with a phase mask and a single-mode fiber. Our results demonstrate the suitability of exploiting the technique for applications in quantum information processing and coherent imaging.

Young's boundary wave theory provides an alternative view of diffraction being an interference of a geometric wave and a boundary wave. Here, we show theoretically and experimentally that the transverse structure of a plane wave diffracted through slits originates solely from the boundary waves. For polygonal slits, we demonstrate that the concept of the ordinary evolute is ill-defined, and we solve this problem by taking the limit of the evolute as the curvature goes to zero. We show that light focuses not on caustic as ordinarily described in catastrophe optics but on regions which we define as second order evolutes. Experimentally, we show that these second order evolutes still correspond to the brightest regions of the diffraction because of the boundary waves at the vertices of the polygon. This research is valuable in the study of diffraction of slits in general and in optical self-healing where the reconstruction of the transverse structure is investigated.

We show that optical beams with orbital angular momentum (OAM) can be generated even with incomplete computer generated holograms (CGHs). These holograms are made such that random portions of them do not contain any information about the beam. We observe that although the beams produced with these holograms are less intense, these beams maintain their transverse intensity profiles. The transverse intensity profiles, as well as a total intensity of the beams, are attenuated by a factor dependent only on the fraction of information retained, f. Also important is that even when f is minute, the topological charge of the beam is not affected. Our result is significant, especially since most methods used to generate beams with OAM for various applications rely on pixelated devices or optical elements with imperfections. Random dead pixels do not affect the transverse intensity and the topological charge. As an extension of our work, we show that superposition of two beams can be created using separate incomplete CGHs interspersed together. Our new method of generating superposed beams may be computationally faster because one only needs to prepare the superposed holograms from already calculated CGHs. It is advantageous for amplitude programmable devices such as a digital micromirror device.

We investigate how beams with orbital angular momentum (OAM) behave under total internal reflection. This is studied in two complementary experiments: In the first experiment, we study geometric shifts of OAM beams upon total internal reflection (Goos-H\"anchen and Imbert-Fedorov shifts, for each the spatial and angular variant), and in the second experiment we determine changes in the OAM mode spectrum of a beam, again upon total internal reflection. As a result we find that in the first case, the shifts are independent of OAM and beam focussing, while in the second case, modifications in the OAM spectrum occur which depend on the input OAM mode as well as on the beam focussing. This is investigated by experiment and theory. We also show how the two methods, beam shifts on the one hand, and OAM spectrum changes on the other, are related theoretically., Comment: 9 pages, 4 figures

A one-order-of-magnitude terahertz (THz) emission enhancement in the transmission geometry, over a 0.7-THz broadband range, was observed in semi-insulating gallium arsenide (SI-GaAs) integrated with a subwavelength one-dimensional metal line array (1DMLA). THz emission of the 1DMLA samples showed an intensity increase and exhibited a full-width-at-half-maximum broadening relative to the emission of the bare substrate. Improved index matching could not account for the observed phenomenon. A nonlinear dependence of the integrated THz emission intensity on the number of illuminated lines and on the pump power was observed. The actual origin of the increased THz emission is still under investigation. At present, it is attributed to extraordinary optical transmission.

I present calculations of reflection beamshifts, Goos-H\"anchen and Imbert-Fedorov shifts, due to the presence of a monolayer graphene on a dielectric media when using a beam with wavelength in the visible range. Measuring the Goos-H\"anchen and Imbert-Fedorov shifts is an alternative method to determine graphene's conductivity. I look at beamshifts for different polarization states ($p$, $s$, $45^0$, $\sigma^+$) and I discuss other possible experimental routes to determine these beamshifts and consequently, the graphene's optical conductivity. The Goos-H\"anchen shifts for visible light I calculated are in good agreement with results of a recent experiment., Comment: 8 pages, 3 figures, accepted for publication in Journal of Optics

Weak amplification is a signal enhancement technique which is used to measure tiny changes that otherwise cannot be determined because of technical limitations. It is based on the existence of a special type of interaction which couples a property of a system, i.e., polarization or which-path information, with a separate degree of freedom, i.e., transverse position or frequency. Unfortunately, the weak amplification process is generally accompanied by severe losses of the detected signal, which limits the applicability of the weak amplification concept. However, we will show here that since the weak measurement concept is essentially an interference phenomena, it should be possible to use the degree of interference to get relevant information about the physical system under study in a more general scenario, where the signal is not severely depleted (high-signal regime). This can widen the range of systems where the weak measurement concept can be applied. In this scenario, which can be called generally weak interference, the idea of weak value does not convey any useful information., 7 pages

Weak measurements are a unique tool for accessing information about weakly interacting quantum systems with minimal back action. Joint weak measurements of single-particle operators with pointer states characterized by a two-dimensional Gaussian distribution can provide, in turn, key information about quantum correlations which can be of relevance for quantum information applications. Here we demonstrate that by employing two-dimensional pointer states endowed with orbital angular momentum (OAM), it is possible to extract weak values of the higher order moments of single-particle operators, an inaccessible quantity with Gaussian pointer states only. We provide a specific example that illustrates the advantages of our method both, in terms of signal enhancement, and information retrieval., 5 pages, accepted for publication in Phys. Rev. Lett

It is known that orbital angular momentum (OAM) couples the Goos-Hanchen and Imbert-Fedorov shifts. Here, we present the first study of these shifts when the OAM-endowed LG(l,p) beams have higher-order radial mode index (p>0). We show theoretically and experimentally that the angular shifts are enhanced by p while the positional shifts are not. Since LG(l,p) modes form a complete basis set for paraxial beams, our results can be used to predict beam shifts of arbitrary modes of light., Accepted for publication in Optics Letters

This Letter reports an experimental and theoretical study of the response of a quadrant detector (QD) to an incident vortex beam, specifically a Laguerre-Gaussian (LG) beam. We have found that the LG beam response depends on the vorticity index l. We compare LG beams with hard-ringed beams and find that at higher l values, the QD response to LG beams can be approximated by its response to hard-ringed beams. Our findings are important in view of the increasing interest in optical vortex beams.

We present experiments on Orbital Angular Momentum (OAM) induced beam shifts in optical reflection. Specifically, we observe the spatial Goos-H\"anchen shift in which the beam is displaced parallel to the plane of incidence and the angular Imbert-Fedorov shift which is a transverse angular deviation from the geometric optics prediction. Experimental results agree well with our theoretical predictions. Both beam shifts increase with the OAM of the beam; we have measured these for OAM indices up to 3. Moreover, the OAM couples these two shifts. Our results are significant for optical metrology since optical beams with OAM have been extensively used in both fundamental and applied research., Comment: 7 pages, 7 figures

We show experimentally that the angular Goos-Hanchen (GH) effect can be easily observed, also without employing its resonant enhancement at Brewster incidence. An s-polarized beam was used to decouple the polarization from the propagation dynamics of the beam. We found that, in this case, the angular GH effect can be strongly enhanced by increasing the angular aperture of the Gaussian beam. Our experiments suggest a route toward observing the angular GH effect for true scalar waves, such as acoustic waves and quantum matter waves.

It is well known that reflection of a Gaussian light beam ($\text{TEM}_{00}$) by a planar dielectric interface leads to four beam shifts when compared to the geometrical-optics prediction. These are the spatial Goos-H\"{a}nchen (GH) shift, the angular GH shift, the spatial Imbert-Fedorov (IF) shift and the angular IF shift. We report here, theoretically and experimentally, that endowing the beam with Orbital Angular Momentum (OAM) leads to coupling of these four shifts; this is described by a $4 \times 4$ mixing matrix., Comment: v2 Version accepted for publication in Phys. Rev. A

We report the first measurement of the Spin Hall Effect of Light (SHEL) on an air-metal interface. The SHEL is a polarization-dependent out-of-plane shift on the reflected beam. For the case of metallic reflection with a linearly polarized incident light, both the spatial and angular variants of the shift are observed and are maximum for -45/45 deg polarization, but zero for pure s- and p-polarization. For an incoming beam with circular polarization states however, only the spatial out-of-plane shift is present., improved figures;removed redundant discussion;change typo in eqn. 2b