We report a simple and robust mechanism that can result in highly directional emission from long-lived resonances in microcavities. By placing a nanoparticle (NP) into the evanescent wave region of microcavities, highly directional outputs with divergence angle ~1.9°-10° can be obtained in single or double directions. The perturbation of NP on evanescent waves preserves the high-quality (Q) fac...

High quality electron bunches were generated by using 2 TW, 80 fs high contrast laser pulses interacting with helium gas targets. In optimized experimental condition, we got tens of MeV monoenergetic electron beams with small energy spread and the normalized emittance reaches 0.07π mm·mrad. Experimental and simulation results show that proper plasma densities make the injection more stable and ...

High-power broad area substrate emitting photonic-crystal distributed feedback (DFB) quantum cascade lasers (QCLs) emitting around 4.73 μm is reported. Two-dimensional centered rectangular photonic-crystal (CRPC) grating is introduced to enhance optical coherence in large area device. Main lobe far-field radiation pattern with a very small divergence angle of about 0.65° × 0.31° is obtained. A ...

Variable selection via penalized estimation is appealing for dimension reduction. For penalized linear regression, Efron, et al. (2004) introduced the LARS algorithm. Recently, the coordinate descent (CD) algorithm was developed by Friedman, et al. (2007) for penalized linear regression and penalized logistic regression and was shown to gain computational superiority. This paper explores...

Some characteristics are reported of a triple-crystal diffractometer with a (+, -, +) setting of Si(220) using mirage diffraction. The first crystal is flat, while the second and third crystals are bent. Basically, the first crystal is used as a collimator, the second as a monochromator and the third as the sample. The third crystal also works as an analyzer. The advantages of this diffractomet...

We propose an ultrafast all-optical technique to control and beam the light emerging from a sub-wavelength slit in a planar gold film by exciting a transient grating in the area around the slit. A FDTD model is used to show how excitation of surface plasmon polaritons by the grating governs the beaming process. Both the grating and the beaming effect are shown to decay on a picosecond time-scal...

The authors theoretically and numerically investigate the beam propagation near the supercollimation frequency s 0 in a photonic crystal made of nonlinear material. Since the value and sign of the equal-frequency-contour curvature which dominates the beam behaviors can be nonlinearly tuned near s , a kind of nonlinear effect is generated. The envelope equation with unique form is also obtained....

Resonant grating filters have been proposed as a promising alternative to multilayer stacks for narrowband free-space filtering. The efficiency of such filters under normal incidence has been demonstrated. Unfortunately, under oblique incidence, the limited angular tolerance of the resonance forbids any filtering applications with use of standard collimated incident beams. Using a multimode pla...

We report the generation of MeV x rays using an undulator and accelerator that are both driven by the same 100-terawatt laser system. The laser pulse driving the accelerator and the scattering laser pulse are independently optimized to generate a high energy electron beam (>200  MeV) and maximize the output x-ray brightness. The total x-ray photon number was measured to be ∼1×10(7), the source ...

At passage of an ultra-high-energy particle through a bent crystal coherent bremsstrahlung is emitted but with characteristic frequencies distributed continuously, in relation with the crystal bend profile. For practical crystals, such radiation can be calculated by the stationary phase approximation technique. The radiation spectrum averaged over the impact parameters is evaluated. Its charact...