Papers by Zohreh Vafapour
Optical and Electronic Cooling of Solids III
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Optics express, 2018
The vertical-external-cavity surface-emitting laser (VECSEL) has shown promise in becoming an eff... more The vertical-external-cavity surface-emitting laser (VECSEL) has shown promise in becoming an efficient source of high power and high beam quality coherent radiation. In order to live up to its true potential, the VECSEL must be thermally managed in order to avoid thermal damage as thermal lensing and filamentation causing preventing it from operating in a single mode regime. For an optically pumped VECSEL, optical cooling presents an elegant solution for thermal management as it does not require electrical or thermal conduction. The goal of optical refrigeration is to achieve radiation balance lasing (RBL) when the active medium is maintained at a steady uniform temperature. In this work, we investigate the active medium characteristics and operating conditions that can lead to RBL in a semiconductor medium and show that to achieve RBL, the gain medium should be engineered to create a density of states that simultaneously allows gain and strong anti-Stokes luminescence. Such a medi...
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Carbon, 2021
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Optical Engineering
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Integrated Optics: Devices, Materials, and Technologies XXII
A tunable slow light thermal modulator using 2D semiconductor metamaterial is presented and inves... more A tunable slow light thermal modulator using 2D semiconductor metamaterial is presented and investigated. We have designed and simulated a terahertz (THz) semiconductor metamaterial (MM) waveguide system; The simulation results show the spectral properties and the group delay of the proposed 2D metamaterial can be tuned by adjusting temperature and the semiconductor used in the waveguide. Our calculations exhibit a significant slow-light effect, based on electromagnetically induced transparency (EIT) effect. By appropriately adjusting the distance between the sub radiant and supper radiant modes, a flat band corresponding to nearly constant group delay (of order of 71) over a narrow bandwidth of THz regime can be achieved. Our analytical results show that the group velocity dispersion (GVD) parameter can reach zero. The simulation results show the incident pulse can be slowed down without distortion owing to the low group velocity dispersion (LGVD). The outstanding result is that, the 2D semiconductor metamaterial is in a high decrease of the group velocity and therefore slow light applications. The proposed compact slow light thermal modulator can avoid the distortion of signal pulse, and thus may find potential applications in slow-light and thermal modulator devices and thermal applications.
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IEEE Sensors Journal
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IEEE Sensors Journal
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Heliyon
The terahertz (THz) region lies between the microwave and infrared regions of the electromagnetic... more The terahertz (THz) region lies between the microwave and infrared regions of the electromagnetic (EM) spectrum such that it is strongly attenuated by water and very sensitive to water content. Here, we numerically present what is to our knowledge the detecting system based on THz reflectance spectral responses data in the diagnosis of in vivo and ex vivo of some cancer's samples such as skin, breast and colon cancer tissue samples. The numerical analysis on the use of semiconductor metamaterial design/device as a complex refractive index (CRI) biosensor have been carried out. We demonstrate the application of terahertz pulse detecting (TPD) in reflection geometry for the study of normal and cancerous biological tissues. THz radiation has very low photon energy and thus it does not pose any ionization hazard for biological tissues. The sensitivity of THz radiation to polar molecules, such as water, makes TPD suitable to study the diseases in human body. By studying the THz pulse shape in the time domain, we have been able to differentiate between diseased and normal tissue for the study of basal cell carcinoma (BCC), breast and colon cancers. These results demonstrate the potential of TPD for the study of skin tissue and its related disorders, both in vivo and ex vivo. Findings of this study demonstrate the potential of TPD to depict breast and colon cancers and both in vivo and ex vivo of skin cancer and encourage further studies to determine the sensitivity and specificity of the technique.
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IEEE Sensors Journal
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IEEE Sensors Journal
Metamaterial perfect light absorbers have received more attention due to their applications in va... more Metamaterial perfect light absorbers have received more attention due to their applications in various fields. In this paper, a metamaterial nanostructure design based on absorption analysis is introduced for the purpose of nonlinear optical liquids sensing which is composed of a sandwich structure of metal-dielectric-metal layer. The nanostructure can display very high absorbance over triple bands at infrared frequencies give rise to large absorbance at different frequencies. The modelling and numerical analysis are carried out using Finite Difference Time Domain (FDTD) method where a genetic algorithm (GA) is used to optimize the geometric parameters of the nanostructure. Numerical simulations show that the proposed perfect absorber with near unity absorbance on all their bands can be tunable designed whereby the dielectric materials of buffer layer, the geometrical parameters of the sandwich nanostructure design, and the polarization of the incident light determine the absorption band of the metamaterial. The triple band perfect absorber is reasonably polarization insensitive and the absorbance remains large even with large angles of incidence. The sensing mechanism of this sensor is detecting changes in the refractive index of the sample environment. This sensor is first optimized for sensitivity using some biomaterial with fixed RI as a sample; this optimized sensor is then used to investigate some nonlinear optical liquid with nonlinear relation in their RI. We achieved a maximum sensitivity of 273 nm/RIU (corresponding to 53 THz/RIU) for Ethanol. This design has considerable potential in similar measurements in various industry such as medical health, and food quality control.
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IEEE Sensors Journal
Plasmonic induced transparency as an interesting physics behind many novel plasmonic devices is u... more Plasmonic induced transparency as an interesting physics behind many novel plasmonic devices is used to design a nano structure composed of graphene and Indium Antimonide (InSb). Due to temperature dependent of graphene and InSb permittivity, the structure is a good candidate for temperature sensor. The sensitivity of the proposed thermal sensor is optimized and the best value for sensitivity is obtained 160(nm/k). The switch application of the proposed structure is also analyzed and a switch with modulation depth of 98% and modulation efficiency of 82% is proposed which has very good values compare to other THz switch reported in literature.
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Optics Express
Radiation balanced lasing (RBL) is an attractive pathway towards the development of high power an... more Radiation balanced lasing (RBL) is an attractive pathway towards the development of high power and good beam quality lasers because heat removal via anti-Stokes luminescence (optical refrigeration) does not require additional connections and components and the heat is dissipated away from the active medium. Optical refrigeration had been demonstrated in the rare-earth doped laser medium but is far more difficult to achieve it in semiconductors laser medium. The main obstacle to achieve RBL in semiconductors is that the most efficient cooling occurs at relatively low carrier densities, while the gain required to sustain laser operation occurs at much higher densities. In this study, we explore the means of resolving this conundrum by separating the optical refrigeration and lasing in temporal, spatial, and/or spectral domains. Time multiplexing involves modulating the pump and operating the laser in pulse modes with lasing and cooling intervals. Space multiplexing involves having separate regions (quantum wells and dots) for lasing and cooling. The spectral multiplexing involves operating with two separate pumps - one for lasing and one for cooling. These methods will be compared in the study with the goal of selecting the optimal path RBL in semiconductor lasers.
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IEEE Transactions on NanoBioscience
Perfect optical metamaterial absorbers (POMMA) utilize intrinsic loss, with the aid of appropriat... more Perfect optical metamaterial absorbers (POMMA) utilize intrinsic loss, with the aid of appropriate structural design, to achieve near unity absorption at a certain wavelength. In all the reported absorbers, the absorption occurs only at a single wavelength or dual/multi-band wavelengths where plasmon resonances are ex-cited in the nanostructure. Here we not only show a single-band perfect absorber but also demonstrate that our proposed design has the ability to be multi-band absorber at the same structure. Furthermore, we numerically demonstrate the proposed POMMA can be utilized as a glucose sensor for refractive index sensing which has more than 225 nm/RIU sensitivity at the infrared frequency regime which is good value. Its polarization-independent absorbance is about 100% at normal incidence for both TE and TM polarization modes. The proposed optical glucose sensor offers great potential to maintain the performance of localized surface plasmon (LSP) sensors in nanostructures in food industry applications.
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IEEE Sensors Journal
We numerically demonstrate a highly sensitive detection of three subtypes of Avian Influenza (AI)... more We numerically demonstrate a highly sensitive detection of three subtypes of Avian Influenza (AI) viruses, namely, H1N1, H5N2, and H9N2 viruses, using terahertz (THz) biosensing metamaterial (MM) that composed of an H-shaped graphene resonator located on a semiconductor film. Three subtypes of AI viruses with different complex refractive indexes (CRIs) were detected at the THz frequency regime. The optical properties of the viruses in the THz frequency range were first measured, and the real and imaginary parts of their CRI are also plotted to investigate the sensing/detecting applications. We observed the resonance frequency shift of the THz MM following the deposition of the viruses on the surface of the proposed design. As an RI sensing application, we show that, with placing different sensing materials in vicinity of the nano sensor/detector device, the reflected resonance frequency changes, which, in turn, leads to measuring the sensitivity of the nano sensor/detector to detect the AI viruses. We investigate the detection of three subtypes of AI viruses with different protein concentrations and different RI values. We observed the resonance-frequency shift of the THz nano bio-sensor/detector following the RI changing of the detected viruses. The resonance shift is higher for the H9N2 virus, which has a relatively large amount of real part of the RI. Thus, the frequency shift decreases with lower amount of the RI real part. Additionally, we show that the magnitude of the reflection spectrum will be enhanced in larger amount of imaginary parts of the RI. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization.
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Journal of the Optical Society of America B
In this paper, a novel semiconductor metamaterial design based on electronically induced reflecti... more In this paper, a novel semiconductor metamaterial design based on electronically induced reflection is proposed, and its thermo-optic applications at the terahertz frequency are investigated. The analytical results show that the peak resonance wavelength position depended very sensitively on the temperature of the structure. The room-temperature operation up to 9 μmK at T=295 K is achieved, which is more than the other values in the literature. It is also shown that by increasing the temperature, the emission decreases, which is promising for thermal regulation, thermal tagging, and labeling applications. Furthermore, we demonstrate numerically that the thermal modulating application can be realized in the proposed semiconductor metamaterial. We achieved 15.4% for the modulation depth and 5.14% for the amplitude modulation depth, which are great values. In general, the work has numerically proved that the thermo-optical design used has very good prospects for various negative differential thermo-optic emission technologies. Furthermore, this semiconductor-based metamaterial structure can develop a path in narrow-band thermo-optic modulating and sensing applications and the like in the future.
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IEEE Sensors Journal
We present a highly sensitive detection of skin cancer using a novel water-based terahertz (THz) ... more We present a highly sensitive detection of skin cancer using a novel water-based terahertz (THz) metamaterial (MM) and a semiconductor film. We apply the application of terahertz pulsed imaging in reflection geometry for the study of skin tissue and related cancers. As a refractive index (RI) sensing application of the proposed device, with placing different sensing materials in the biosensor design, the effective RI will also change that in turn leads to measuring the sensitivity of the biosensor to detect the normal skin and basal cell carcinoma. The RI figure of merit (FOM) value of the proposed device is much higher than that of the sensor using a semiconductor film to detect biomarkers in the literature. Significantly, the sensitivity increases by about 117 $\mu {\mathrm{ m}}$ /RIU and the RI FOM increases by more than 20.53. This results from a combination of size-related factors, leading to field enhancement accompanying strong field localization. We observed the resonance-frequency shift of the THz MM following the RI changing of the detected skin. The dip reflectance resonance has a blue shift for normal skin. Finally, we suggest that this water-based MM can be used to the control of the gene expression. The advantage of our design depends on two factors. First, we used the MM structure that has micro-scale, and the smaller the size of the structure, the more sensitive to the changes in the RI. Second, we used water in our structure, which is very well-suited to the human body, highly bio-absorbable and inexpensive, and abundantly found in nature.
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Journal of the Optical Society of America B
By incorporating a dielectric material into a semiconductor thin film, we have demonstrated an op... more By incorporating a dielectric material into a semiconductor thin film, we have demonstrated an optically reconfigurable classical electromagnetically induced reflectance (Cl-EIR) effect in planar metamaterials (MMs) functioning at the far-infrared (far-IR) frequency regime. The proposed far-IR sensor is a microstructure composed of a semiconductor thin film and three dielectric antennas. Numerical analyses based on the far- and near-field interaction are investigated in detail. The coupling between the subradiant and supperradiant modes verify the existence of the Cl-EIR effect. The Cl-EIR frequency could be tuned by changing the surrounding medium, the temperature of the semiconductor layer, the semiconductor material, and the substrate material. Therefore, the proposed complementary MM microstructure, based on a semiconductor featuring tunable reflectance windows, may open up new avenues for designing tunable temperature sensors, optical and biomedical sensors, switches, and slow light devices.
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Plasmonics, 2016
A graphene-based metamaterial with tunable electromagnetically induced transparency is numericall... more A graphene-based metamaterial with tunable electromagnetically induced transparency is numerically studied in this paper. The proposed structure consists of a graphene layer composed of H shape between two cut wires, by breaking symmetry can control EIT-like effects and by increasing the asymmetry in the structure has strong coupling between elements. It is important that the peak frequency of transmission window can be dynamically controlled over a broad frequency range by varying the chemical potential of graphene layer. The results show that high refractive index sensitivity and figure of merit can be achieved in asymmetrical structures which is good for sensing applications. We calculated the group delay and the results show we can control the group velocity by varying the S parameter in asymmetrical structure. The characteristics of our system indicate important potential applications in integrated optical circuits such as optical storage, ultrafast plasmonic switches, high performance filters, and slow-light devices.
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Journal of Luminescence
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Papers by Zohreh Vafapour