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As resist feature sizes have decreased and the performance demands on chemically amplified photoresists have increased the role of the photoacid generator (PAG) in determining overall resist performance has become increasingly apparent. Over the past 20 years a variety of different types of PAG's have been introduced as researchers have sought to optimize properties such as acid strength, acid volatility, diffusion length, wavelength response, solubility etc. PAGs that produce very strong organic acids are widely used, in part because of requirements for high photospeed resists. Most of these acid generators are based on perfluoroalkyl sulfonic acid based onium salts. In an effort to identify and characterize alternative PAGs we have investigated the performance of a variety of photoacid generators that are not based on sulfonic acids. In this report we will describe the relative reactivities of these PAGs under a variety of exposure wavelengths and processing conditions including acid diffusion proprieties and photospeed measurements.

We report transmission measurements at cryogenic temperatures for 4 broad-band filters of the Mauna Kea Observatories (MKO) near-infrared filter set and 5 narrow-band filters. The spectral scans were collected using the multi-mode IR instrument of the TNG telescope (NICS) in which these filters are permanently mounted and commonly used for astronomical observations. We determined the transmission curves at a temperature of 78K and found no significant red-leak up to 2.6 microns, the data are available in electronic form on the TNG web page. We also estimated the variation of the wavelength response with the incidence angle and found it compatible with an effective refractive index of about 2., Comment: 3 pages, 2 figures, link to transmission data files, A&A in press

We demonstrate the first In0.53Ga0.47As/InP p‐doped quantum well infrared photodetector (QWIP). This detector has the shortest wavelength response, λp=2.7 μm, ever achieved in a QWIP and operates at normal incidence.

We propose and experimentally demonstrate a novel method which, for the first time to our knowledge, makes it possible to tailor the wavelength response of a waveguide grating coupler. Such grating couplers may be used to improve the efficiency of broad-band quantum-well infrared photodetectors and solar cells.

In this paper, we present a theoretical study on the effect of the angle of a tilted Bragg grating written in a 2 x 2 symmetric fused fiber coupler. Coupling coefficients and wavelength response curves show that the grating angle is critica1 in determining the behavior of the component. For a particular type of coupler, a tilt of 0.4' is sufficient to degrade component performance.

Many of the fundamental characteristics of the recording and reproducing processes can be observed by considering the wavelength response and the pulse response of the magnetic recording channel. The first part of this paper presents some experimental results. The second part consists of a discussion of wavelength response analysis followed by an estimation of head-medium interface parameters based on the experimental measurements. Finally, the assumptions and approximations throughout the analyses are given.

UV-sensitive products which undergo a colour change on exposure to UV radiation are available for use by the general public. We have evaluated SunCheck patches of various sensitivities, and Tanscan UV sensor cards, in terms of their temperature stability, wavelength response and response to sunlight. The products exhibited no perceptible colour change when the temperature was maintained at 45 degrees C for 4 hours; on exposure to monochromatic radiation, the sensitivity peaked at a wavelength of 335 and 355 nm for SunCheck and Tanscan, respectively; the response to sunlight under clear conditions was reasonably consistent, with the coefficient of variation for each type of material ranging between 12.5 and 27%. These products are based on the incorrect concept that there is a 'safe' dose of UV radiation. Thus, they cannot be recommended to the public as a reliable way of reducing the risk of skin cancer.

Metal stripe waveguides in silica, operating in the fundamental long-range mode and at optical free-space wavelengths near 1550nm, are discussed in detail. Straight and curved waveguides having various stripe geometries are modeled. Au, Ag, and Al are compared as metals for the stripe. The wavelength response of waveguides is computed. The impact of index asymmetry is determined and discussed. The results generated and collected herein should be useful to the design of low-loss metal stripe waveguides for integrated plasmonic applications in silica and cladding materials of comparable index.

A new method for the fabrication of a singlemode fibre wavelength independent Y-junction is described; through asymmetrically tapering a pre-assembled Y-junction precursor, the splice point is drawn into the waist region of the device and low-loss is ensured. The lowest loss and flattest wavelength response for such a device is reported.

The effect of surface recombination velocity on the short wavelength response of the tandem junction solar cell is investigated theoretically. The analysis predicts approximately the same dependence of the short-circuit current on surface recombination velocity as for a conventional p-n junction solar cell. It is concluded that the experimentally observed improvement in the blue response of the tandem junction solar cell is probably due to a small surface recombination velocity as a result of the absence of front-surface metallization.

Results of calculations are presented which illustrate the effect of the location of an ideal winding on the wavelength response of probe heads from a perpendicular recording medium with a permeable underlayer. Calculated wavelength responses represent the theoretical limits for the response of practical probe heads with practical windings. A numerical estimate of possible improvement of readback response of probe heads is presented.

The readback response of a perpendicular recording system utilizing a medium with a soft magnetic underlayer (SMUL) had been investigated using rigorous two-dimensional theory. The results are as follows. 1) Changes in the medium thickness (with a SMUL) effect radical changes in the wavelength response of the heads. 2) For a thin medium, the effective gap of a ring head becomes twice its geometrical gap. 3) The combination of probe head and medium with SMUL has adequate resolution only if the recording medium thickness is an order of magnitude less than probe thickness. 4) The foregoing combination has a potential advantage over longitudinal recording on conventional thin media with respect to the absolute value of readback output.

A hypothetical action spectrum for the regression of lesions in photochemotherapy of psoriasis is proposed. An ideal detector should have a wavelength response which matches this action spectrum but this is generally not the case with commercially available photometers. The problems that may arise by indiscriminate use of such detectors are discussed, together with a suggested solution.

The absolute calibration, linearity, angular response and wavelength response of three different commercially available UVA meters have been evaluated. The meters exhibited wide variations in accuracy in determining UVA irradiance, combined with significant differences in response at different angles and wavelengths. It is considered that these variations may lead to uncertainties in ultraviolet radiation dosimetry when assessing the relation between the risk of cutaneous carcinoma associated with oral psoralen photochemotherapy and UVA dose.

Directional growth was induced in the conchocelis phase of Porphyra umbilicalis (L.) J. Ag. by prolonged unilateral light. The filaments of the conchocelis exhibited negative phototropism when irradiated with monochromatic light of wavelengths between 400–500 nm. Fragmented filaments were used for the experiments on phototropism; after a growing period of 4 wk, these filaments showed a phototropic reaction to continuous unilateral light within 1 day. The photoropic response increased in proportion to the logarithm of the photon flux density of the monochromatic light. The wavelength response curve showed similarities with phototropic action spectra found in the literature except that there was an additional peak near 400 nm. Phototropism was also demonstrated in ten other species of red algae, the rhizoids of which showed a negative response. The filaments of some species grew towards light.

The paper is confined to a discussion of the mechanical limits imposed on magnetic recording heads by the required performance specification. The performance criteria of a multi-track head are normally: sensitivity and the variation in sensitivity between tracks, the short wavelength response, high-frequency losses, bias sensitivity, and cross-talk between adjacent tracks. The manufacturing problems associated with multi-track heads are discussed in relation to the effects of mechanical variations on the head performance.

Ga1−xInxAs alloys in the composition range 0≤x≥0.52 and band‐gap (Eg) range of 1.38 to 0.74 eV were activated with Cs and O2. Samples of different carrier concentrations were investigated. For band gaps down to about 0.8 eV, the photothreshold was equal to the band gap. The longest wavelength threshold determined was 1.58 μm. To the best of our knowledge, this represents the longest wavelength response yet achieved for photoemission into vacuum from a III‐V compound. The surface escape probability, B, was derived from the quantum yield data for each sample. The B‐vs‐Eg data were analyzed according to a surface escape model which includes the effects of (i) a finite‐width initial energy distribution of photoexcited carriers, (ii) the bent‐band region and (iii) various types of surface potential barriers. Surface escape probability data pertaining to a single doping density could be explained by a model that includes only a work‐function barrier or simple step potential. However, in order to explain the dat...

Recently developed 3-5 compound semiconductor photocathodes show promise of substantial advantages over conventional photocathodes in increased yield and longer wavelength response. This paper reviews the physical principles of operation, preparation, and activation of these new types of photocathode. Also discussed are current fabrication techniques, problem areas, practical difficulties, and operating characteristics of experimental cathodes.

For photoconductors in which the dominant noise is generation‐recombination noise, it is shown that the signal‐to‐noise ratio is proportional to expβEi/2kTD, where Ei is the threshold response of the photoconductor, TD is its temperature, and β is a constant between unity and one‐half. If longer wavelength response is desired (smaller Ei) without sacrificing signal‐to‐noise ratio, this can only be achieved by lowering TD. Similarly, for any given Ei, the generation‐recombination noise can be reduced to an arbitrarily low level by lowering TD sufficiently. Expressions are obtained for the optimum value of Ei under typical operating conditions.

A LIPS tape of CrO 2 particles was prepared through the follwing steps: 1) a perpendicular orientation over the entire thickness by the previous "VAST" method (Vertical magnetic orientation-AC demagnetization-Smoothing period -Train), 2) a short radiation heating only in the shallow surface layer and 3) a magnetic reorientation to the longitudinal direction only in the inside layer, still in a low viscosity state. Their magnetic data show that the thickness of the perpendicular surface layer can be controlled to any suitable thin value by the heating condition. Their wavelength response shows both high density and wide band characters.

Barium-ferrite fine-particle-coated perpendicular magnetic recording tapes have been experimentally fabricated. Typical tapes have M s = 120 - 130 emu/cc, H c = 600 - 1500 Oe and perpendicular squareness ratio M_{r\perp}/M_{s} larger than 0.9. Tape recording performances were measured with a perpendicular head as well as With a ring-shaped head. A good short wavelength response, D 50 = 76k FRPI, which has never been attained by longitudinally oriented particulate tapes, was obtained; The relationship between perpendicular squareness ratio and output was also investigated to show the importance of perpendicular orientation for attaining a higher recording density.

Achieving both high resolution and high read/write efficiency has been tried with a rather thick single-pole-head film core having the sensitive (ordinary) trailing edge and the less sensitive leading edge in the neighborhood of which a degradation of the magnetic flux density (Bs) is made. The degradation is made by laminating several sputtered layers of different alloy constitution of Co 1-x Zr x (x = 0.17-0.32). The whole film core consists of this degradation region of 4.2 μm thick and high permeability Co 0.85 Zr 0.03 Nb 0.12 region of 5.0 μm thick. Observed shallowing of the reproduce nulls in the wavelength response with the rather thick core shows a possible compatibility of the resolution and the efficiency.

We report In1−xGaxAsyP1−y/InP photodiode detectors with external quantum efficiencies of 50–70% without antireflection coating. The short‐ and long‐wavelength response limits of these very efficient detectors can be compositionally tuned to lie anywhere in the wavelength range 0.9

Output response of thin film heads was analyzed using wavelength response to determine the optimum pole tip length for both low peak shift and high resolution. From the analytical analysis, thin film heads were designed and fabricated. The experimental results very much agree with the theoretical results. We conclude that by selecting the trailing pole to be thicker than the leading pole we can achieve optimum results for certain linear density requirements. We also observe that heads with thin poles provide better results at both low frequency and high frequency, while heads with thick poles work better at mid range frequency.

The fabrication and performance of a stable single-mode transmissive 8×8 star coupler is described. The device exhibits very low excess loss (0.13 dB), good coupling uniformity (0.73 dB) and low near-end crosstalk (>64 dB). The star coupler is fabricated from eight lengths of single-mode fibre, by forming 3 dB fused coupling regions between appropriate fibre pairs. A Table of insertion loss measurements is presented, together with graphs showing the wavelength response between 1.2 and 1.7 μm.

A short review of bias methods for the magnetoresistive head (MRH), all based on the rotation of the magnetization, is given, and the properties of the various methods are discussed. A novel bias method is proposed which avoids many disadvantages of the former since it is based on the rotation of the current with the aid of slanted conductors, covering the MRH. Measured and calculated static curves are given for this new configuration, for which the name "Barber Pole" is proposed. The Barber Pole turns out to be more linear than a field-biassed MRH. The wavelength response of a Barber Pole is calculated and found to be very similar to that of a normal MRH; this is confirmed by measurements. A two terminal track sensing head, based on the new biassing principle is described.

Barium ferrite media have created a lot of interest for digital and analog applications because of their potential to achieve high recording densities. To fully exploit this potential, it is necessary to develop media with good perpendicular orientation and to employ high saturation narrow gap heads. It is possible, however, to obtain very good recording performance utilizing Ba‐ferrite media which are nonoriented or only partially oriented and ordinary ferrite heads for high‐density digital recording applications. In this study, we investigated the performance of such media in rigid disk form using conventional and narrower gap ferrite heads, and obtained much better short wavelength response than that obtained from high‐coercivity cobalt‐modified iron oxide media. The overwrite modulation of these media, however, is only marginally acceptable. The modulation noise observed is much larger for longitudinally oriented than for perpendicularly oriented media. A simple model is proposed to explain the origin...

The perpendicular recording mode is still a candidate for obtaining higher densities. Best recording results on a double-layer (DL) medium must be expected from using a probe head (PH). This contribution provides an analysis of the write-read performance of one-sided PHs that do not use an auxiliary pole on the back of the medium. Analytical as well as numerical models were used to calculate the effects of saturation and medium thickness on the write fields. Experimental verification of the modeling results was obtained by measuring the wavelength response of many W-shaped PHs on DL media. Combining this with the calculated response, we obtained a semi-empirical relation between the pole nulls, pole thickness and the pole-to-backlayer distance. It reveals a PH behaviour very different from a ring head (RH). The pole thickness calculated from the measured pole-null wavelengths showed a very close agreement with the optically determined value. The calculated head efficiencies are very small, as was confirmed experimentally, and need improvement before the PH has an output comparable with a RH.

The wavelength response of a reproducing head can be estimated quantitatively by the superposition of isolated pulses in perpendicular magnetic recording, because recording demagnetization does not occur. In this paper, the resolution of reproduction of a single-pole head is theoretically investigated for various thicknesses of the main-pole and compared with the experimental results. It is also shown that the 50 % down density D 50 is influenced by the virtual spacing, which depends on the thickness of the Co-Cr layer of a double-layered medium. To realize the high resolution of a single-pole head, the main-pole of 0.15 μm in thickness has been made of a Co-Zr-Nb amorphous film. The 50 % down density D 50 of 135 kFRPI could be reached by combining this head with the double-layered medium having a thinner Co-Cr layer of 0.25 μm.

The wavelength dependence of the ac biased recording sensitivity is calculated utilizing a model in which both longitudinal and vertical record fields are considered. Even though the effects of demagnetization fields and spreads in particle switching fields are neglected, the calculation yields excellent quantitative agreement with measurements on extremely well-oriented CrO 2 and γFe 2 O 3 magnetic tapes.

A new method is described whereby extremely short effective gap lengths of ring type reproducing heads used in high resolution magnetic recording instruments can be determined. The method is based on comparison of the frequency or wavelength response of the short gap head with that of a second head of longer gap length which can be conveniently measured by the first null-point method reported previously. Experimental results for the measurement of a head gap of the order of 20 × 10−6 in are given as an illustration.

The twisting of an asymmetric fused tapered single-mode fibre coupler is found to decrease the maximum coupled power, in addition to the usual shift in the wavelength response. This effect can be used to optimise a wavelength-flattened coupler's performance during or after coupler elongation.

Long-wavelength HgCdTe photodiodes operating at 20 K have been developed with quantum efficiencies >40%, bandwidths >500 MHz and a calculated heterodyne NEP = 6 × 10−20 W/Hz for a local oscillator power of 100 μW at 28 μm. A theoretical analysis along with wavelength response, pulse response and noise data are described.

Note: Conference Digest of Sixteenth Int. Conference on Infrared and Millimeter Waves, Lausanne, Switzerland, August 1991, SPIE Vol. 1576, 94 - 95 (1991) Reference CRPP-CONF-1991-016 Record created on 2008-05-13, modified on 2017-05-12

We propose a novel concept for a MUX/DEMUX array based on microresonators with reconfigurable bandwidth and wavelength response. Initial experimental results on a single MR element prove its suitability for flexible-grid applications.

Summary form only given.We have demonstrated a micro-taper based long-period grating with very narrow bandwidth optical response of 7 nm and extinction >20 dB. The wavelength response and bandwidths can be redesigned by choosing appropriate periods and grating lengths.

A two-dimensional head model with an infinitely permeable core wrapped with an infinitesimally thin winding provides the best possible resolution. The readback wavelength response for a model when an ideal winding covers the magnetic core up to the core tips is the autoconvolution of the response of a head with the same core and the winding at infinity. Usage of this relationship facilities the evaluations of theoretical limits of characteristics of real heads.

In infrared reflectography of paintings infrared-to-visible image translation systems are used, operating around 2.0 microns; paint layers become most transparent in that spectral region to detect an underdrawing beneath. Earlier work was successfully carried out with a Barnes Infrared Camera equipped with a lead sulphide detector peaked at about 2.0 microns [1]. Later an infrared vidicon was used manufactured by Heimann PTW in a television system [2]. This vidicon is not ideal because it is not peaked at 2.0 microns-in fact its responsivity extends only to about 1.8 microns. In practice, however, reflectograms were often comparable with those obtained with the earlier Barnes system, although penetration of malachite-containing paint was inferior and interference of overlying paint layers more pronounced. Hori et al. have reported the development of an infrared vidicon with a multi-layer PbO-PbS-sensitive target showing a very short time-lag, a higher resolution and a wavelength response up to 2.0 microns [3]. This vidicon would have been preferable but it is not commercially available. Recently, however, an infrared vidicon manufactured by Hamamatsu Inc. [4] has been made commercially available with a wavelength response up to 2.4 microns. This vidicon has indeed the responsivity required for optimal infrared reflectography; in addition it can be estimated that its signal current when using a 0.8 micron cut-on 100

Summary form only given, as follows. The author reviews device technologies that may benefit from the use of photorefractive materials. These include optical data storage, associative memory, neural networks, optical crossbars, and optical defect inspection. For these technologies, the author defines the properties desired of photorefractive materials. Photorefractive materials exhibit a broad range of properties. These properties determine the utility of the material in any particular device application. Materials with a property of special appeal to an application may be deficient in another important property. It is therefore essential to understand the properties demanded by certain applications, and to mount a research program to determine the ability to alter the properties of the base materials with which one can work. As a result of this activity, a great deal can be learned about the accuracy of the solid-state models used to project the capabilities of these materials. A research program on photorefractive materials is described that addresses such properties as retention time, diffraction efficiency, speed, and wavelength response. The effect of doping on these parameters is demonstrated, and some fundamental shortcomings in the classical band transport model are noted. >

A rhomb consisting of two dense flint equilateral prisms may be used to deviate light and introduce polarization effects analogous to those of the Fresnel rhomb which displaces light. Because of the high index of the prism material (μD=1.650), the wavelength response of the prism rhomb is superior to that of the classical low index Fresnel rhomb. Perpendicular transit of glass surfaces and invariance of the direction of the emergent light apply for both types, but in other respects the rhombs are complementary. In addition, the necessary prisms are widely available commercially.