High-accuracy and rapid azimuth calibration for polarizing elements in ellipsometry by differential spectral analysis on the ellipse azimuth.

We propose an accurate and rapid azimuth calibration method for polarizing elements in ellipsometry. Over 200 calibrations were achieved simultaneously at different wavelength points in a spectral range of 550-650 nm without any calibrated element. The azimuth of the polarizer was determined from the differential spectral analysis on the ellipse azimuth of reflected light. The information of the ellipse azimuth is experimentally acquired in the spectral range by a rotating polarizing element and a spectrometer. The presented method was performed and verified with Si and Au bulk, respectively, showing reliability and feasibility for efficient and reliable calibration in ellipsometry.

Generalized ellipsometry characterization of Ag nanorod arrays prepared by oblique angle deposition.

Silver nanorods arrays (AgNRs) prepared by oblique angle deposition were characterized by the generalized ellipsometry method in the spectral range from 370 to 950 nm. Three structure models were used to fit the ellipsometry data, the uniaxial model, the biaxial orthorhombic model, and the biaxial monoclinic model. Unlike the uniaxial model reported in most literature, the biaxial models are found to give better fitting results. The optical properties along the three principle axes are different: along long axis it displays predominantly metallic behavior; along one short axis it approaches to a lossless dielectric while along the other it behaves as an absorbance dielectric. The AgNRs also demonstrate epsilon-near-zero property with the real part of dielectric constant along the rod being very close to zero at wavelength of 416 nm, which is expected to be tuned with changing of the vapor incident angles.

A coma-free super-high resolution optical spectrometer using 44 high dispersion sub-gratings.

Unlike the single grating Czerny-Turner configuration spectrometers, a super-high spectral resolution optical spectrometer with zero coma aberration is first experimentally demonstrated by using a compound integrated diffraction grating module consisting of 44 high dispersion sub-gratings and a two-dimensional backside-illuminated charge-coupled device array photodetector. The demonstrated super-high resolution spectrometer gives 0.005 nm (5 pm) spectral resolution in ultra-violet range and 0.01 nm spectral resolution in the visible range, as well as a uniform efficiency of diffraction in a broad 200 nm to 1000 nm wavelength region. Our new zero-off-axis spectrometer configuration has the unique merit that enables it to be used for a wide range of spectral sensing and measurement applications.

Microstructure-Induced Anisotropic Optical Properties of YF3 Columnar Thin Films Prepared by Glancing Angle Deposition.

Yttrium fluoride (YF3) columnar thin films (CTFs) were fabricated by electron beam evaporation with the glancing angle deposition method. The microstructures and optical properties of YF3 CTFs were studied systematically. The YF3 films grown at different deposition angles are all amorphous. As the deposition angle increases, the columns in YF3 CTFs become increasingly separated and inclined, and the volume fraction of YF3 decreases, resulting in lower refractive indices. This phenomenon is attributed to the self-shadowing effect and limited adatom diffusion. The YF3 CTFs are optically biaxial anisotropic with the long axis (c-axis) parallel to the columns, the short axis (b-axis) perpendicular to the columns, and the other axis (a-axis) parallel to the film interface. The principal refractive index along the b-axis for the 82°-deposited sample is approximately 1.233 at 550 nm. For the 78°-deposited sample, the differences of principal refractive indices between the c-axis and the b-axis and between the a-axis and the b-axis reach the maximum 0.056 and 0.029, respectively. The differences of principal refractive indices were affected by both the deposition angle and the volume fraction of YF3.

Strong optical absorption of a metallic film to induce a lensing effect in the visible region.

In this work, the two-dimensional profile of the light transmission through a prism-like metallic film sample of Au was measured at a wavelength of 632.8 nm in the visible intraband transition region to verify that, beyond the possible mechanisms of overcoming the diffraction limit, a strongly nonuniform optical absorption path length of the light traveling in the metal could induce a lensing effect, thereby narrowing the image of an object. A set of prism-like Au samples with different angles was prepared and experimentally investigated. Due to the nonuniform paths of the light traveling in the Au samples, lens-effect-like phenomena were clearly observed that reduced the imaged size of the beam spot with decreasing light intensity. The experimental measurements presented in the work may provide new insight to better understand the light propagation behavior at a metal/dielectric interface.

Ultrahigh-resolution spectrometer based on 19 integrated gratings.

Optical spectrometers play a key role in acquiring rich photonic information in both scientific research and a wide variety of applications. In this work, we present a new spectrometer with an ultrahigh resolution of better than 0.012 nm/pixel in the 170-600 nm spectral region using a grating-integrated module that consists of 19 subgratings without any moving parts. By using two-dimensional (2D) backsideilluminated complementary metal-oxide-semiconductor (BSI-CMOS) array detector technology with 2048 × 2048 pixels, a high data acquisition speed of approximately 25 spectra per second is achieved. The physical photon-sensing size of the detector along the one-dimensional wavelength direction is enhanced by a factor of 19 to approximately 428 mm, or 38912 pixels, to satisfy the requirement of seamless connection between two neighboring subspectral regions without any missing wavelengths throughout the entire spectral region. As tested with a mercury lamp, the system has advanced performance capabilities characterized by the highest k parameter reported to date, being approximately 3.58 × 104, where k = (working wavelength region)/(pixel resolution). Data calibration and analysis as well as a method of reducing background noise more efficiently are also discussed. The results presented in this work will stimulate further research on precision spectrometers based on advanced BSI-CMOS array detectors in the future.