Perpendicular Gratings Research Articles

Taming the Distribution of Light in Gate-All-Around Semiconductor Devices.

Optical metrology is ubiquitous, but image-based methods cannot resolve features of dimensions much smaller than the wavelength. However, it has recently been demonstrated that light can be nanofocused into subwavelength semiconducting lines by setting the incident polarization along the direction of these lines. This Letter extends the previous studies to systems with two perpendicular gratings, as found e.g. after replacement gate processing of gate-all-around (GAA) field-effect transistors (FETs). We show that besides the nanofocusing effect, the incident polarization also offers control over which array of lines the light couples into. The interaction of the incident light occurs with the semiconducting lines to which the polarization is parallel with remarkably low interference from the existence of another perpendicular grating. We demonstrate the use of this effect with Raman spectroscopy to simultaneously extract the SiGe volume and the strain in the Si forksheet channels and in the SiGe layers of GAA FETs.

Choice of Grating Orientation for Evaluation of Peripheral Vision.

ABSTRACTPurposePeripheral resolution acuity depends on the orientation of the stimuli. However, it is uncertain if such a meridional effect also exists for peripheral detection tasks because they are affected by optical errors. Knowledge of the quantitative differences in acuity for different grating orientations is crucial for choosing the appropriate stimuli for evaluations of peripheral resolution and detection tasks. We assessed resolution and detection thresholds for different grating orientations in the peripheral visual field.MethodsResolution and detection thresholds were evaluated for gratings of four different orientations in eight different visual field meridians in the 20-deg visual field in white light. Detection measurements in monochromatic light (543 nm; bandwidth, 10 nm) were also performed to evaluate the effects of chromatic aberration on the meridional effect. A combination of trial lenses and adaptive optics system was used to correct the monochromatic lower- and higher-order aberrations.ResultsFor both resolution and detection tasks, gratings parallel to the visual field meridian had better threshold compared with the perpendicular gratings, whereas the two oblique gratings had similar thresholds. The parallel and perpendicular grating acuity differences for resolution and detection tasks were 0.16 logMAR and 0.11 logMAD, respectively. Elimination of chromatic errors did not affect the meridional preference in detection acuity.ConclusionsSimilar to peripheral resolution, detection also shows a meridional effect that appears to have a neural origin. The threshold difference seen for parallel and perpendicular gratings suggests the use of two oblique gratings as stimuli in alternative forced-choice procedures for peripheral vision evaluation to reduce measurement variation.

Two-dimensional plasmonic nanosurface for photovoltaics

In this paper, we investigate a two-dimensional corrugated plasmonic nanosurface for efficient light trapping in a photovoltaic cell. Inspired by a well-known one-dimensional grating nanosurface, the present configuration is composed of two perpendicular gratings in the metal film that intersect to yield cross-shaped nanoelements. The surface corrugation is then covered by a silicon film. An additional degree of freedom can be introduced into the design by interrupting the grid in both directions. We show that this extra spacing between the array elements can be used to tune the absorption properties of the nanosurface. By including the effect of the solar spectrum, we demonstrate how this two-dimensional configuration is more efficient than its one-dimensional counterpart in terms of the actual short circuit photocurrent density. Finally, we propose possible extensions of this structure design, which can further enhance the solar cell performance.

Lasing Action in Optically Written Two-Dimensional DFB Gratings

Gratings for laser applications in poly(styrenc-co-4-vinylbenzyl-thiocyanate) (PST-co-VBT) are being optically recorded by deep UV lithography (λ = 266nm). The gratings writing configuration is based on interference patterning of this novel-type holographic material. Using lower intensity laser irradiation, refractive index gratings are produced in PST-co-VBT by an UV induced photoisomerization SCN-NCS. Laser irradiation with higher pulse energies directly produces surface relief gratings via laser ablation. Holographically recorded structures of dye-doped PST-co-VBT (DCM:PST-co-VBT) are designed for second order distributed feedback (DFB) operation resulting in low threshold organic lasers devices. 2D DFB lasers with two perpendicular gratings having different grating periods are investigated with respect to tuneable DFB lasing.

Formation of Microstructure in SiO2 Thin Film by a Femtosecond Laser Pulse

Non-erasable micro grating structures were successfully encoded in amorphous SiO2 thin films on silicon wafers by colliding a pair of focused pulses split from a single femtosecond pulse from a 10 Hz mode-locked Ti:sapphire laser with a regenerative amplifier (wavelength; λ=800 nm, pulse duration; 100 fs, pulse energy; ∼ 3 mJ/pulse). The encoded periodic spacing varied with the angle, θ, between the two crossed pulses according to d=λ/(2sin (θ/2)). A minimum periodic spacing of ∼ 430 nm was achieved for a laser wavelength of 800 nm. Volume compaction resulting from structural alterations of the silica network in amorphous SiO2 induced by intense femtosecond laser irradiations was responsible for the formation of these grating structures. Further, an array of dot structures was fabricated in amorphous SiO2 thin films by a encoding two perpendicular gratings.

Design considerations of large aperture perpendicular gratings semiconductor ring lasers

A new laser geometry, recently demonstrated, is analyzed. The laser cavity consists of two orthogonally oriented diffraction gratings faced by two plane boundaries, such as cleaved facets. It is shown that such lasers may operate at a single, very high mode order with excellent modal discrimination.

Amnesia for the mccollough effect following unilateral electroconvulsive therapy: implications for laterality

The hemispheric lateralization of retrograde amnesia following unilateral electroconvulsive therapy (ECT) was measured by a novel nonverbal probe, the McCollough effect, which allowed equal and exclusive access to each hemisphere. Alternating exposure to perpendicular gratings of complementary colors (e.g., red vertical stripes alternated with green horizontal stripes) will cause subsequently presented black and white gratings to appear colored hours or even days later (the McCollough effect). Three of the patients examined (3 of 10) lost the effect in just the half visual field contralateral to the treatment side when unilateral nondominant ECT was interposed between the induction of the effect and the its test. Six patients lost the effect bilaterally following unilateral ECT. One patient retained a bilateral aftereffect. This patient had by far the shortest seizure (18 sec). Nine of 10 comparison patients, also suffering from major depression but without ECT intervening between induction and test, showed good bilateral retention of the McCollough effect. The remaining comparison patient showed no retention. These results imply that despite bilateral cortical spread of seizure activity, unilateral nondominant ECT has effects that are most pronounced over the stimulated hemisphere.

Binocular interaction in the VEP to grating stimulation: I. Orientational effects

The orientational effects of monocular stimulation with sinusoidal grating patterns were studied with transient VEP technique in 10 subjects with normal vision and binocular functions. No significant variation in amplitude with orientation was obtained. The latency for 45 degrees (oblique) orientation was slightly longer than the latency for other orientations. The orientational effects on binocular interaction in dichoptic stimulation were determined with sinusoidal grating patterns at a reversing rate of 1.9 and 2.1 Hz for each eye respectively. The binocular interaction was assessed as the binocular/monocular ratio of the VEP amplitude for each eye. There was a significantly reduced binocular interaction for dichoptically presented perpendicular gratings as compared to parallel gratings at the spatial frequencies of 2, 4 and 6 cycles/degree, when mean values of the whole group of subjects were statistically analysed. A broad orientation tuning of about 45 degree was found for the binocular interaction at 4 cycles/degree for the group as a whole, although tuning was hard to establish in the VEP of each individual. This compares well with other neurophysiological and electrophysiological data but is broader than the orientation tuning demonstrated psychophysically.