Interline Transfer CCD Camera Research Articles

Signal-to-noise ratio improvements in laser flow diagnostics using time-resolved image averaging and high dynamic range imaging

Two alternative image readout approaches are demonstrated to improve the signal-to-noise ratio (SNR) in temporally resolved laser-based imaging experiments of turbulent phenomena. The first method exploits the temporal decay characteristics of the phosphor screens of image intensifiers when coupled to an interline-transfer CCD camera operated in double-frame mode. Specifically, the light emitted by the phosphor screen, which has a finite decay constant, is equally distributed and recorded over the two sequential frames of the detector so that an averaged image can be reconstructed. The characterization of both detector and image intensifier showed that the technique preserves the correct quantitative information, and its applicability to reactive flows was verified using planar Rayleigh scattering and tested with the acquisition of images of both steady and turbulent partially premixed methane/air flames. The comparison between conventional Rayleigh results and the averaged ones showed that the SNR of the averaged image is higher than the conventional one; with the setup used in this work, the gain in SNR was seen to approach 30 %, for both the steady and turbulent cases. The second technique uses the two-frame readout of an interline-transfer CCD to increase the image SNR based on high dynamic range imaging, and it was tested in an unsteady non-reactive flow of Freon-12 injected in air. The result showed a 15 % increase in the SNR of the low-pixel-count regions of an image, when compared to the pixels of a conventionally averaged one.

Characterization of a Commercial, Front-Illuminated Interline Transfer CCD Camera for use as a Guide Camera on a Balloon-Borne Telescope

We report results obtained during the characterization of a commercial front-illuminated progressive scan interline transfer CCD camera. We demonstrate that the unmodified camera operates successfully in temperature and pressure conditions (-40°C, 4 mBar) representative of a high altitude balloon mission. We further demonstrate that the centroid of a well-sampled star can be determined to better than 2% of a pixel, even though the CCD is equipped with a microlens array. This device has been selected for use in a closed-loop star-guiding and tip-tilt correction system in the BIT-STABLE balloon mission.

Interline transfer CCD camera for gated broadband coherent anti-Stokes Raman-scattering measurements

Use of an interline transfer CCD camera for the acquisition of broadband coherent anti-Stokes Raman-scattering (CARS) spectra is demonstrated. The interline transfer CCD has alternating columns of imaging and storage pixels that allow one to acquire two successive images by shifting the first image in the storage pixels and immediately acquiring the second image. We have used this dual-image mode for gated CARS measurements by acquiring a CARS spectral image and shifting it rapidly from the imaging pixel columns to the storage pixel columns. We have demonstrated the use of this dual-image mode for gated single-laser-shot measurement of hydrogen and nitrogen CARS spectra at room temperature and in atmospheric pressure flames. The performance of the interline transfer CCD for these CARS measurements is compared directly with the performance of a back-illuminated unintensified CCD camera.

Measurement of the temporal evolution of periodic induced displacement derivatives using stroboscopic electronic speckle-shearing interferometry

Single pulsed subtraction electronic speckle-shearing pattern interferometry is used to measure the time evolution of deformations induced by periodic impulse loading on a metal plate. This is accomplished with a stroboscopic system based on a pulsed laser and an interline-transfer CCD camera running at 60 frames/s. In a few seconds, a sequence of hundreds of interferograms is recorded with an effective sampling time interval of some tens of microseconds. We describe the experimental setup used to generate the transient deformation on the metal plate and also the synchronization of laser pulses and image acquisition. Several correlation fringe patterns are presented, showing the time evolution of the deformation. Finally, these data are used to calculate optical phase maps and displacement derivative fields for different times after the application of the dynamic load on the object.

Simultaneous imaging of temperature and mole fraction using acetone planar laser-induced fluorescence

Imaging of concentration with acetone PLIF has become popular in mixing investigations. More recently, studies of the temperature dependences of acetone fluorescence have enabled quantitative imaging of temperature using single- or dual-wavelength excitation strategies. We present here the first demonstration of simultaneous imaging of temperature and mole fraction with acetone PLIF. Laser excitation is at 248 and 308 nm; the resulting fluorescence images are captured by an interline transfer CCD camera capable of acquiring two frames with a separation in time of as little as 500 ns. In addition to adding temperature imaging capability, this dual-wavelength approach enables mole fraction to be accurately measured in non-isothermal flows. Tests in a heated turbulent jet demonstrate the ability to record instantaneous mole fraction and temperature structure. The expected correspondence of the temperature and concentration fields is observed, and mean values of these quantities derived from image averaging show the expected radial and centerline profiles as the jet becomes fully developed.

Operation modes of an interline-transfer camera in pulsed subtraction video speckle interferometry

When pulsed lasers are applied in subtraction video speckle interferometry, the interline-transfer CCD camera used to acquire the primary interferograms to be subtracted can be operated in different modes. The features of each operation mode are discussed. It is shown that the visibility of the correlation fringes produced by subtraction depends on the operation mode in which the interline-transfer camera is used. By subtracting in different ways two primary interferograms recorded for an in-plane configuration using a cw laser, it is shown that results favor the use of CCD cameras operated in the noninterlaced field and noninterlaced frame modes.

Double-pulse subtraction TV holography

The fringe visibility in pulsed subtraction and addition TV holography is described and compared. Correlation fringe patterns, obtained by conventional double-pulse addition TV holography, are characterized by their relatively poor quality. The fringe visibility is significantly improved by applying subtraction in combination with the double-pulse technique. This is achieved by using a standard interline transfer CCD camera. Double-pulse subtraction TV holography is especially useful for subfringe measurements, and vibration amplitudes of less than λ/50 have been detected on raw double-pulse subtraction interferograms.