One- and two-dimensional (1D and 2D) nanorippled structures produced in silicon by ultraviolet laser irradiation were investigated using atomic force and scanning electron microscopy. One- and two-beam illumination of the substrate was used to generate the nanostructures. Single-beam irradiation was done using p-polarized laser light, while the two-beam incidence was achieved employing a Lloyd’s mirror arrangement to reflect part of the beam onto the substrate. The structures were characterized by direct measurement of the ripple spacing or by measurements done on the fast Fourier transform of their atomic force microscopy (AFM) images. Under single-beam illumination, only 1D gratings were generated on the substrate surface. The grating lines were perpendicular to the projection of the electric field of the incident light on the substrate surface. For the two-beam illumination, it was very difficult to obtain the Lloyd’s mirror characteristic interference pattern due to the poor coherency of the laser employed. Nonetheless, the use of a Lloyd’s mirror not only enhanced the production of rippled structures strongly but also produced 2D gratings. The gratings generated with this arrangement are many millimeters long and cover the entire laser illuminated area. In contrast with one-beam illumination, linearly polarized light was not required to promote the rippled structures. Experimental evidence strongly suggests the following: (1) the p component of the laser light is responsible for ripple formation; (2) ripples can propagate with increasing number of pulses; and (3) the ripple structure is produced while the silicon is melted. The occurrence of melting is further supported by a computer simulation of the thermal field during the laser pulse. An estimate done using the lubrication approximation indicates that liquid is displaced from the hotter into the cooler regions by the gradient of surface tension. At angles of incidence equal or larger that 50°, the ripple spacing data indicate that incident laser light promotes the generation of plasma oscillation in the liquid silicon. These surface electromagnetic waves are responsible for the formation of ripples with lines that run parallel to the projection of the wave vector of the incident wave on the substrate surface. The simple irradiation procedure used to produce these nanostructures opens the possibility of using them as a template for ordering other nanostructures on a vast scale.

A multispectral image camera captures image data within specific wavelength ranges in narrow wavelength bands across the electromagnetic spectrum. Images from a multispectral camera can extract additional information that the human eye or a normal camera fails to capture and thus may have important applications in precision agriculture, forestry, medicine and object identification. Conventional multispectral cameras are made up of multiple image sensors each fitted with a narrow passband wavelength filter and optics, which makes them heavy, bulky, power hungry and very expensive. The multiple optics also create image co-registration problem. Here, we demonstrate a single sensor based three band multispectral camera using a narrow spectral band RGB colour mosaic in a Bayer pattern integrated on a monochrome CMOS sensor. The narrow band colour mosaic is made of a hybrid combination of plasmonic colour filters and heterostructured dielectric multilayer. The demonstrated camera technology has reduced cost, weight, size and power by almost n times (where n is the number of bands) compared to a conventional multispectral camera.

The goal of this work is to investigate the thermal effects of femtosecond laser (fs-laser) ablation for the removal of carious dental tissue. Additional studies identify different tooth tissues through femtosecond laser induced breakdown spectroscopy (fsLIBS) for the development of a feedback loop that could be utilized during ablation in a clinical setting. Scanning Election Microscope (SEM) images reveal that minimal morphological damages are incurred at repetition rates below the carbonization threshold of each tooth tissue. Thermal studies measure the temperature distribution and temperature decay during laser ablation and after laser cessation, and demonstrate that repetition rates at or below 10kHz with a laser fluence of 40 J/cm would inflict minimal thermal damage on the surrounding nerve tissues and provide acceptable clinical removal rates. Spectral analysis of the different tooth tissues is also conducted and differences between the visible wavelength fsLIBS spectra are evident, though more robust classification studies are needed for clinical translation. These results have initiated a set of precautionary recommendations that would enable the clinician to utilize femtosecond laser ablation for the removal of carious lesions while ensuring that the solidity and utility of the tooth remain intact.

Nanofabrication of x-ray diffractive optics using electron beam lithography requires a complex process of electron exposure optimization and resist development. Thermal scanning probe lithography (TSPL) offers a high resolution, maskless, gray scale patterning method with reduced complexity. Thin diffractive optics with high efficiency for the extreme ultraviolet (EUV) and soft x-ray (SXR) photon range could be fabricated by combining TSPL with a single etching step if the TSPL resist, polyphthalaldehyde (PPA), can be used as an etch mask to direct-etch the pattern into a substrate using reactive ion etching. This condition critically depends on high etch selectivity between the substrate and the PPA, because TSPL resolution deteriorates as the PPA patterning depth increases beyond tens of nanometers. In this work, the authors have evaluated the etch selectivity for PPA and Si3N4 using SF6/C4F8 gases and the influence of process parameters, including gas flow rate, vacuum pressure, radio frequency bias power, and inductively coupled plasma power. The experimental results indicate that an etch selectivity of 7 (Si3N4:PPA) is achievable, and the authors demonstrate that diffractive optics for EUV/SXR can be fabricated in only two steps.