Advances in filter technology for multiphoton microscopy

Investigation of a broadband TiO 2/SiO 2 optical thin-film filter for hybrid solar power systems

Bandpass filters are indispensable to the development of advanced optical and electro-optical systems used in space, defense, and terrestrial applications. In this paper, wideband deep cutoff bandpass filter of 750-900nm was designed and prepared by ion beam sputtering deposition technology. Long wave pass filter with high transmittance from 750 to 900nm and low transmittance from 400 to 730nm was designed and prepared on one side of the HB720 substrate. Short wave pass filter with high transmittance from 750 to 900nm and low transmittance from 930 to 1100nm was designed and prepared on the other side of the HB720 substrate. From the measured transmittance curve, the average transmittance was above 96% from 750nm to 900nm, the transmittance at the wavelength of 728nm and 928nm was less than 0.1%. The results indicated that high quality bandpass filter can be manufactured using the combination method of long-wave and short-wave filters.

Optical interference filters are widely used in optics for various applications. Depending on the optical system specifications, either edge filters or band-pass filters are required. In this last category, special attention is paid to narrow band transmission filters which use is greatly expanding in both telecommunication and spectrometry. In this work, narrow band transmission filters are proposed which performance is varied along the filter surface. These variable filters allow the construction of compact spectrometers that are useful in all applications where both weight and dimensions are required to be very low. Transmission filters operating in a wide wavelength range, visible and shortwave near infrared, are described. Their peak transmittance is linearly moved in one direction along the component surface, within a total length smaller than 10 mm. The filter structure is composed of a thin-film multilayer stack containing both metal and dielectric materials.

Advanced optical bandpass filters for the Hubble Space Telescope (HST) Advanced Camera for Surveys (ACS) have been developed on a filter-by-filter basis through detailed studies which take into account the instrument's science goals, available optical filter fabrication technology, and developments in ACS's charge-coupled-device (CCD) detector technology. These filters include a subset of filters for the Sloan Digital Sky Survey (SDSS) which are optimized for astronomical photometry using today's charge-coupled-devices (CCD's). In order for ACS to be truly advanced, these filters must push the state-of-the-art in performance in a number of key areas at the same time. Important requirements for these filters include outstanding transmitted wavefront, high transmittance, uniform transmittance across each filter, spectrally structure-free bandpasses, exceptionally high out of band rejection, a high degree of parfocality, and immunity to environmental degradation. These constitute a very stringent set of requirements indeed, especially for filters which are up to 90 mm in diameter. The highly successful paradigm in which final specifications for flight filters were derived through interaction amongst the ACS Science Team, the instrument designer, the lead optical engineer, and the filter designer and vendor is described. Examples of iterative design trade studies carried out in the context of science needs and budgetary and schedule constraints are presented. An overview of the final design specifications for the ACS bandpass and ramp filters is also presented.

Novel bandpass filter for far UV-C emitting radiation sources

Multi-layer reflective thin film filters optimized for oblique incidence angles were deposited on glass substrates using Electron Beam evaporation technique with in situ thickness monitoring. The present study involves deposition and optical characterization of 5 layered multi-layer structures of TiO 2 -Al 2 O 3 and TiO 2 -SiO 2 having different thicknesses for varied wavelength ranges in the visible region. Three TiO 2 -SiO 2 multi-layer thin film filters were deposited having peak reflectance at 480 nm, 540 nm and 675 nm respectively corresponding to light sources in the blue, green and red wavelength regions. Similarly, a TiO 2 -Al 2 O 3 multi-layer was fabricated having peak reflectance of around 64% at 610nm. These filters were deposited at an elevated temperature of 250° C in an oxygenated reactive environment for better adhesion, mechanical strength and proper stoichiometr y. Reflectance measurements of these multi-layer filters at oblique incidence angles reveal high reflectance of around 70 ~ 75% with a reasonably broad reflection band which can have wide applications in beam steering, shaping and folding applications in various complex optical systems facing constrained space and we ight requirements. Keywords: Thin films, optical coatings, interference filters, fo lding mirror, multi-layers, electron beam deposition.

Modern high energy laser mirrors require very high reflectances (greater than 99.9%) for operation. Simple metallic coatings cannot give a high enough reflectance, so further dielectric layers must be added to enhance the reflectance. Such mirrors may be several meters in diameter and strongly curved, making uniform coatings difficult to deposit. The reflectance is not critically dependent on the thicknesses of the layers, but a 1% thickness error for a typical 6-layer design gives a wavefront phase error of .01X. Worse, this error is a function of wavelength; the wavefronts may be very different in visible light than at the infrared design wave-length. Due to a nonlinear relation between coating thickness and the optical phase change on reflection, the wavefront in the visible may look very little like the coating thickness distribution that produces it. A technique for determining coating thickness distributions for an IR coating from interferograms taken at 2 or more visible wavelengths has been developed. The usefulness of the method has been studied by a series of calculations, and the means of obtaining good accuracy are described.

Integrated optical filters for infrared electrooptical gas sensors

In situ fabrication of ZnO nanorods/Ag hybrid film with high mid-infrared reflectance for applications in energy efficient windows

In visible light communication (VLC), using multiple colors is an efficient way to enhance data rate, leading to multi-color VLC (MC-VLC). However, the performance of MC-VLC is jeopardized by the spectral overlaps of different colors. Thin-film optical filters, as the key component of MC-VLC systems, are usually adopted to separate colors. The passband bandwidth (BW) and center wavelength (CWL) of optical filters are critical to mitigate the crosstalk among colors and, thus, must be carefully designed. Moreover, due to the intrinsic wavelength shift of the CWL with the varying of the angle of incidence, it is challenging to support mobility for MC-VLC. In this paper, we consider a joint design of multiple optical filters for MC-VLC by properly selecting the BW and CWL of each filter. We first investigate the optical filter design for a fixed receiver location. Then, to support mobility, we propose two robust optical filter designs, namely, statistically and worst case robust designs, which do not rely on the exact receiver location. Efficient methods are developed to solve the corresponding design problems and obtain the optimized optical filters. Compared with the existing optical filters, the proposed optical filters exhibits much better performance in various scenarios.

We have conducted an extensive series of laser damage measurements on highly reflective (HR) dielectric coatings which have yielded 1064-nm thresholds as high as 40 J/cm for 8- to 10-ns pulses at pulse-repetition frequencies (PRF) of 10 Hz. Moreover by laser conditioning these coatings with subthreshold pulses the thresholds of some coatings were raised to levels exceeding 70 J/cm. These are the highest threshold dielectric HR coatings that we have tested in this regime. The coatings were originally developed to produce HR-overcoated metal mirrors for free-electronlaser (EEL) app1icationsat high PRF. Our tests included coatings deposited on both dielectric substrates and molybdenum (Mo) substrates. In each category we also examined coatings with a pre-coat of Mo between the substrate and the HR stack. The improved dielectric HR stacks effectively shielded the Mo from the laser irradiation so that the thresholds of virtually all Mo samples exceeded levels of the best dielectric-enhanced and dielectric-HR-coated metal mirrors we have tested to date. In addition to the low PRF measurements we also conducted 1064-nm damage tests at 6-kHz PRF using 65-ns pulses from the Kilroy damage test facility. The coatings survived thermal loading of fluences ranging from 2 to 10 J/cm2 with respective small spot sizes on the order of 1 . 2 to 0. 3 mm (1 /e? diameter). 1.© (1991) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Dichroic mirrors, as core optical elements, are widely used in biomedical testing instruments based on the principles of absorbance detection, fluorescence detection and Raman detection. In this paper, the application principle of dichroic mirrors for biomedical detection was introduced, and some key technical indexes for high-performance dichroic mirrors were proposed according to their application characteristics. With the equivalent layer substitution method, a dichroic mirror film system of high-performance based on two conventional materials was designed. Using the plasma assisted reactive magnetron sputtering technology, the dichroic mirror film system with 146 layers was coated, and a kind of dichroic mirror with some important technical indicators such as high steepness (<1%), depolarization (polarization separation <3.5nm), wide range of high transmission (T>96% range > 300nm) was manufactured. The influence of wavefront distortion of dichroic mirror on imaging was described in detail. Our dichroic mirrors can meet the performance of low transmitted wavefront distortion (TWD<λ/4) and low reflected wavefront distortion (RWD<λ/2). The manufactured dichroic mirror products showed satisfying application results when used in high-end medical testing instruments with fine imaging requirements.

Recent studies have demonstrated that the tumor suppressor PTEN (phosphatase and tensin homolog deleted from chromosome 10), the antagonist of the phosphosphoinositol-3-kinase (PI3K) signaling cascade, is susceptible to H2O2-dependent oxidative inactivation. This study describes the use of redox-engineered cell lines to identify PTEN as sensitive to oxidative inactivation by mitochondrial H2O2. Increases in the steady state production of mitochondrial derived H2O2, as a result of manganese superoxide dismutase (Sod2) overexpression, led to PTEN oxidation that was reversed by the coexpression of the H2O2-detoxifying enzyme catalase. The accumulation of an oxidized inactive fraction of PTEN favored the formation of phosphatidylinositol 3,4,5-triphosphate at the plasma membrane, resulting in increased activation of Akt and modulation of its downstream targets. PTEN oxidation in response to mitochondrial H2O2 enhanced PI3K signaling, leading to increased expression of the key regulator of angiogenesis, vascular endothelial growth factor. Overexpression of PTEN prevented the H2O2-dependent increase in vascular endothelial growth factor promoter activity and immunoreactive protein, whereas a mutant PTEN (G129R), lacking phosphatase activity, did not. Furthermore, mitochondrial generation of H2O2 by Sod2 promoted endothelial cell sprouting in a three-dimensional in vitro angiogenesis assay that was attenuated by catalase coexpression or the PI3K inhibitor LY2949002. Moreover, Sod2 overexpression resulted in increased in vivo blood vessel formation that was H2O2-dependent as assessed by the chicken chorioallantoic membrane assay. Our findings provide the first evidence for the involvement of mitochondrial H2O2 in regulating PTEN function and the angiogenic switch, indicating that Sod2 can serve as an alternative physiological source of the potent signaling molecule, H2O2.

Hyperspectral imaging was originally developed for use in remote sensing applications. More recently, it has been applied to biological imaging systems, such as fluorescence microscopes. The ability to distinguish molecules based on spectral differences has been especially advantageous for identifying fluorophores in highly autofluorescent tissues. A key component of hyperspectral imaging systems is wavelength filtering. Each filtering technology used for hyperspectral imaging has corresponding advantages and disadvantages. Recently, a new optical filtering technology has been developed that uses multi-layered thin-film optical filters that can be rotated, with respect to incident light, to control the center wavelength of the pass-band. Compared to the majority of tunable filter technologies, these filters have superior optical performance including greater than 90% transmission, steep spectral edges and high out-of-band blocking. Hence, tunable thin-film optical filters present optical characteristics that may make them well-suited for many biological spectral imaging applications. An array of tunable thin-film filters was implemented on an inverted fluorescence microscope (TE 2000, Nikon Instruments) to cover the full visible wavelength range. Images of a previously published model, GFP-expressing endothelial cells in the lung, were acquired using a charge-coupled device camera (Rolera EM-C2, Q-Imaging). This model sample presents fluorescently-labeled cells in a highly autofluorescent environment. Linear unmixing of hyperspectral images indicates that thin-film tunable filters provide equivalent spectral discrimination to our previous acousto-optic tunable filter-based approach, with increased signal-to-noise characteristics. Hence, tunable multi-layered thin film optical filters may provide greatly improved spectral filtering characteristics and therefore enable wider acceptance of hyperspectral widefield microscopy.

Currently, WDM thin-film filter has become one of the hottest areas in optical communication. In this research, the structure of parallel plate thin-film filter and wedge thin-film filter are designed and transmittance curve is simulated. Then samples of thin-film filter are tested and the performances are analyzed.