CCD Readout Noise Research Articles

Low Count Detection for EELS Spectrum by Reducing CCD Read-out Noise

Journal Article Low Count Detection for EELS Spectrum by Reducing CCD Read-out Noise Get access Mitsutaka Haruta, Mitsutaka Haruta Kyoto University, Uji, Kyoto, Japan Search for other works by this author on: Oxford Academic Google Scholar Yoshifumi Fujiyoshi, Yoshifumi Fujiyoshi Kyoto University, Uji, Kyoto, Japan Search for other works by this author on: Oxford Academic Google Scholar Takashi Nemoto, Takashi Nemoto Kyoto University, Uji, Kyoto, Japan Search for other works by this author on: Oxford Academic Google Scholar Akimitsu Ishizuka, Akimitsu Ishizuka HREM Research Inc., Higashimatsuyama, Saitama, Japan Search for other works by this author on: Oxford Academic Google Scholar Kazuo Ishizuka, Kazuo Ishizuka HREM Research Inc., Higashimatsuyama, Saitama, Japan Search for other works by this author on: Oxford Academic Google Scholar Hiroki Kurata Hiroki Kurata Kyoto University, Uji, Kyoto, Japan Search for other works by this author on: Oxford Academic Google Scholar Microscopy and Microanalysis, Volume 26, Issue S2, 1 August 2020, Pages 1202–1204, https://doi.org/10.1017/S1431927620017328 Published: 01 August 2020

Extremely low count detection for EELS spectrum imaging by reducing CCD read-out noise

Extremely low count detection for EELS spectrum imaging is required to overcome problems with electron irradiation and widen the range of available applications. We have made a systematic statistical study of the reduction of CCD noise for EELS. We propose a calculation method to estimate the properties of noise and a procedure to reduce it. Since the dominant noise is a practically random component, it can be reduced by subtracting the population mean of the dark reference and a summation over an appropriate number of spectra, depending on the standard deviation of the noise. A gain-averaging method can further improve the signal-to-noise (SN) ratio. It is thereby demonstrated that a high-SN spectrum can be obtained even for a single-count core-loss signal. The present method would be useful for measuring low signal spectrum such as monochromated spectra and for radiation sensitive materials.

Measurement of thermospheric temperatures using OMTI Fabry\u2013Perot interferometers with 70-mm etalon

Fabry–Perot interferometer (FPI) is an instrument that can measure the temperature and wind velocity of the thermosphere through observations of airglow emission at a wavelength of 630.0 nm. The Solar-Terrestrial Environment Laboratory/Institute for Space-Earth Environmental Research, Nagoya University, has recently developed four new ground-based FPIs. One of those FPIs, possessing a large-aperture etalon (diameter: 116 mm), was installed in Tromsø (FP01), Norway, in 2009. The other three small FPIs, using 70-mm-diameter etalons, were installed in Thailand (FP02), Indonesia (FP03) and Australia (FP04) in 2010–2011. They use highly sensitive cooled-CCD cameras with 1024 × 1024 pixels to obtain interference fringes. However, appropriate temperature has not been obtained from the interference fringes using these new small-aperture FPIs. In the present study we improved the analysis procedure of temperature determination using these FPIs. Each of FPIs measures north, south, east and west directions repeatedly by rotating two mirrors mounted on top of the FPI. We estimated center pixel of laser fringe and airglow fringes for each direction and found significant differences in the center pixel locations (a few pixels) among the measurement directions. These differences are considered to be caused by movement of the scanning mirror on the top of the optics, resulting in mechanical distortion of the optics body. By calculating the fringe center separately for each direction, we could correct these center pixel variations and determine the temperature with random errors of 10–40 K. This new method was employed to the all measurements from four FPIs after 2009 and provided temperatures with reasonably small errors. However, we found that temperatures below 400 K were obtained associated with weak airglow intensities and concluded using a model calculation that they are due to contamination of OH line emissions in the upper mesosphere. By defining an appropriate threshold of the fringe peak count, we successfully eliminated these unrealistic temperature values, and the corrected temperature values became comparable to those provided by the MSIS-90E and GAIA models.Graphical abstractTemperatures obtained by the FPIs and comparison with MSIS-E90 and GAIA models. Average temperatures (solid lines) and number of data (dashed lines) obtained at (a) Tromsø, (b) Chiang Mai, (c) Kototabang and (d) Darwin for the shown interval Thick lines show temperatures averaged for every 15 minutes obtained by FP01-04. Data obtained when the airglow intensity was very low (less than 3-sigma of CCD read-out noise) were removed. The error bars indicate standard deviations of the whole data. Thin lines and dotted lines show that obtained by the MSIS-E90 model and the GAIA model, respectively, at an altitude of 250 km.

Dual crystal x-ray spectrometer at 1.8 keV for high repetition-rate single-photon counting spectroscopy experiments

With the recent development of high-repetition rate x-ray free electron lasers (FEL), it is now possible to perform x-ray scattering and emission spectroscopy measurements from thin foils or gasses heated to high-energy density conditions by integrating over many experimental shots. Since the expected signal may be weaker than the typical CCD readout noise over the region-of-interest, it is critical to the success of this approach to use a detector with high-energy resolution so that single x-ray photons may be isolated. Here we describe a dual channel x-ray spectrometer developed for the Atomic and Molecular Optics endstation at the Linac Coherent Light Source (LCLS) for x-ray spectroscopy near the K-edge of aluminum. The spectrometer is based on a pair of curved PET (002) crystals coupled to a single pnCCD detector which simultaneously measures x-ray scattering and emission in the forward and backward directions. The signals from single x-ray photons are accumulated permitting continuous single-shot acquisition at 120 Hz.

Error analysis of laser beam quality measured with CCD sensor and choice of the optimal threshold

Accurate measurement of beam quality is very important in different areas of laser applications. Take the far-field Gaussian spot as an example, the calculation error formulas of peak Strehl ratio and beam quality factor β are derived in the present of various error sources, such as background photon noise, CCD pixel's non-ideal sampling, CCD dark voltage, read-out noise of CCD, signal photon noise and measurement window size. The calculation errors of laser beam quality changing with various error sources are presented in theory and the corresponding numerically simulated results are given. Theoretical and simulated results show that when the threshold is set at NB¯+σB, with NB¯ standing for average value of the error sources and σB standing for mean-square value of the fluctuation in error sources, the lowest calculating error of laser beam quality could be achieved.

From Differential Image Motion to Seeing

ABSTRACTThe theory of the differential image motion monitor (DIMM), a standard and widely spread method of measuring astronomical seeing, is reviewed and extended. More accurate coefficients for computing the Fried parameter from the measured variance of image motion are given. They are tested by numerical simulations that show that any DIMM measures Zernike tilts, not image centroids as generally assumed. The contribution of CCD readout noise to image motion variance is modeled. It can substantially bias DIMM results if left unsubtracted. The second most important DIMM bias comes from the used exposure time, which is typically not short enough to freeze image motion completely. This effect is studied quantitatively for real turbulence and wind profiles, and its correction by interlaced short and long exposures is validated. Finally, the influence of turbulence outer scale reduces image size in large telescopes by 10% or more compared to the standard theory; new formulae to compute FWHM and half‐energy diameter of the atmospheric point‐spread function that take into account outer scale are provided.

Study of CCD mosaic configurations for the ILMT: Astrometry and photometry of point sources in the absence of a TDI corrector

The image deformations induced by the time-delay integration (TDI) mode, used with a CCD camera at the prime focus of a Liquid Mirror Telescope (LMT), can be corrected for by a system of lenses, simultaneously with the optical aberrations. However, before adopting the design of a TDI corrector, we may wonder what is the importance of the TDI image deformations and how to possibly reduce these by choosing optimal mosaic congurations of CCDs, covering an equivalent eld of view. In a rst step, we have simulated the point spread function (PSF) deformation due to the TDI mode only, for dierent selected mosaic congurations. We have then estimated the importance of the astrometric and photometric errors induced by the TDI deformation. By simulating star elds with the same synthetic PSF and taking into account realistic sources of noise (cf. CCD readout noise, photon noise and sky background), we have derived the limiting magnitudes for photometry and astrometry for the case of a 4 m LMT.

Effect of CCD readout noise in astronomical speckle imaging

A theoretical and experimental comparison of photon-countingcameras and CCD's for use in astronomical speckle imaging wasperformed. Photon-counting cameras able to detect single-photonevents typically exhibit a lower quantum efficiency (QE) and suffersaturation effects at high light levels. In contrast, CCD's offera high QE and virtually unlimited photon-count rate. However CCD'sare limited at lower light levels by noise associated with the readoutprocess. Speckle-imaging performance was quantified by derivationof the signal-to-noise ratio (SNR) of the power spectrum and theKnox-Thompson product to include CCD readout noise. Ground-basedtelescope observations at various light levels were obtained with anadvanced, high-speed, low-noise CCD camera to verify SNRexpressions. The useful operating ranges for these two camera typeswere compared by consideration of the effects of QE, readout noise, andmaximum photon-count rate. Although photon-counting camerascontinued to dominate low-light-level applications, CCD's are shown tooffer significant improvements over photon-counting cameras for a widerange of light levels. Future reductions of readout noise will further improve CCD speckle-imaging performance.