Y coupled terahertz quantum cascade lasers

Here we demonstrate a Y coupled terahertz (THz) quantum cascade laser (QCL) system. The two THz QCLs working around 2.85 THz are driven by independent electrical pulsers. Total peak THz output power of the Y system, with both arms being driven synchronously, is found to be more than the linear sum of the peak powers from the individual arms; 10.4 mW compared with 9.6 mW (4.7 mW + 4.9 mW). Furthermore, we demonstrate that the emission spectra of this coupled system are significantly different to that of either arm alone, or to the linear combination of their individual spectra.Comment: 9 pages, 3 figure

Reversible Mode Switching in Y coupled Terahertz Lasers

Electrically independent terahertz (THz) quantum cascade lasers (QCLs) are optically coupled in a Y configuration. Dual frequency, electronically switchable emission is achieved in one QCL using an aperiodic grating, designed using computer-generated hologram techniques, incorporated directly into the QCL waveguide by focussed ion beam milling. Multi-moded emission around 2.9 THz is inhibited, lasing instead occurring at switchable grating-selected frequencies of 2.88 and 2.92 THz. This photonic control and switching behaviour is selectively and reversibly transferred to the second, unmodified QCL via evanescent mode coupling, without the transfer of the inherent grating losses

Characteristics of Pulsatile Blood Flow Through 3-D Geometry of Arterial Stenosis

AbstractA numerical simulation is carried out to demonstrate the significant changes of flow behaviour for two different severities of arterial stenosis. Two stenosis levels of 65% and 85% are considered by area. The blood is considered as flowing fluid and assumed to be incompressible, homogeneous and Newtonian, while artery is assumed to be a rigid wall. The transient analysis is performed using ANSYS-14.5. The flow pattern, wall shear stress (WSS), pressure contours, and Centre-line velocity distribution are observed at early-systole, peak-systole and diastole for better understanding of arterial disease. Wall Share Stress distribution shows that as severity increases, sharing of flow also increases for all cases. Thus maximum stress is exerted in throat region at peak systole. The pressure distribution demonstrates that at all cases 85% stenotic artery creates more force than 65% stenotic artery at their pre-stenotic region. Interestingly, a recirculation region is visible at the post stenotic region in 85% stenotic artery for all cases and recirculation region increases with the decrease of the inlet flow velocity. Analysis indicates that the significant flow changes happen in the post stenotic region

Load Management for Voltage Control Study Using Parallel Immunized-computational Intelligence Technique

The increase of power demand is a crucial issue in the power system community in many parts of the world. Malaysia has also witnessed the familiar scenario due to the current development throughout the country has invited the urgency of increase in the power supply. Since Malaysia practices vertical system; where the electricity is supplied by only one utility, load management is an important issue so that the delivery of electricity is implemented without discrimination. Parallel Computational Intelligence will be developed which can alleviate and avoid all the unsolved issues, highlighting the weakness of current schemes. Parallel Computational Intelligence is developed to manage the optimal load in making sure the system maintains the stability condition, within the voltage limits. This paper presents evolutionary programming (EP) technique for optimizing the voltage profile. In this study, 3 algorithms which are Gaussian, Cauchy and Parallel EP were developed to solve optimal load management problem on IEEE 26-bus Reliability Test System (RTS). Results obtained from the study revealed that the application of Parallel EP has significantly reduced the time for the optimization process to complete

Unexplained recurrent hematuria and clot retention following transurethral resection of the prostate

Severe hemorrhage following a prostatectomy is a rare and serious complication. A 60-year-old male with recurrent hematuria and clot retention following transurethral resection of the prostate  (TURP) which led to anemia presented at our department and was treated with repeated clot evacuation and fulguration and lastly re-resection and fulguration succeed to stop bleeding. At 18 months follow-up, the patient had recovered well. We concluded that re-resection and fulguration on fresh tissue without opening the venous sinusoids should be considered as one of the effective treatment of choice in recurrent hemorrhage following TURP.   

Longitudinal Computer Generated Holograms for Digital Frequency Control in Electronically Tunable Terahertz Lasers

A transverse computer-generated hologram (CGH) diffracts and provides flexible control of incident light by steering it to any point in the projected image plane - i.e. CGHs are able to direct the light to where it is needed and away from where it is not. In addition, the number of resolvable points in the image projection plane is a function of the CGH's pixel count. Here we report a longitudinal CGH (LCGH), a photonic structure, which swaps the ability to steer light toward fixed spatial points for digital control in the frequency domain. This is of particular interest in the context of tunable lasers. In this regard, an LCGH offers two important degrees-of-freedom (DOFs): 1) provides high-resolution wavevector or k space resolution within the Brillouin zone; 2) enables full control to define or modify the reflectivity at each resolvable k point, so attaining a target spectral response. We demonstrate the flexibility of our LCGH approach by achieving purely electronic tuning between six digitally-selected operating frequencies in a single section terahertz (THz) quantum cascade laser (QCL). These switchable single-frequency devices will simplify combining the power and flexibility of THz QCLs with spectroscopic applications, such as remote sensing, spectral analysis, and both security and medical imaging.Comment: 17 pages, 4 Figures, submitted to Nature Photonic