SIT vidicon

The observations of the lithium resonance line at x6708.8 A were carried out with a SIT vidicon detector attached to the coudi spectrometer of the 1.5 m telescope of the Tartu Astrophysical Observatory. The sample of stars observed consists of 70 K0 - K5 and 75 MO - M4 giants. A set of spectra of K giants with different strengths of lithium resonance doublet is shown in Fig. 1. 

Figure 5. Fiber-optic vidicon spectrometer. (1) Nitrous oxide/acetylene flame (2) SIT vidicon detector (3) Fiber-optic input lenses (4) Fiber-optic entrance slit system (5) 0.5-m Czemy-Turner monochromator (6) Optical multichannel analyzer (7) Oscilloscope display.

Described in this paper are three aspects of our work dealing with the verification of the performance of the system that may aid other users of the OMA 1) the measurement of the deterioration of the image caused by pulsing the SIT vidicon and how to eliminate the deterioration, 2) the measurement of pincushion distortion, and 3) the use of a triangular mask in a spinning rotor to simulate an optical density wedge. 

Not only can errors in absorbance measurements arise from non-linearity in the detector circuitry, but distortion in the linearity of the position of channel detector elements can lead to a corresponding distortion of the measured intensity profile. The geometric distortion of the SIT vidicon, as stated in the specification sheet supplied by the OMA manufacturer, is typically 2 channels between channels 100 and 400 for a 2.5 mm high image centered on the tube. This distortion is sufficient to require correction of data obtained for experiments with steep concentration gradients in our system. 

For the SIT vidicon the line-scan amplitude Is reduced to give a 5 by 12.5 mm scanning pattern and adjusted so as to center the image on the tube face. Adjustment of the symmetry control is especially important. Misadjustment will c tuse a distortion in the intensity profile of a knife-edge image at the bottom it will appear rounded or it will fall below the zero intensity level. 

Ruled Line Target. For the measurement of pincushion distortion, we decided to examine a ruled line target. It turned out that the intensity profiles obtained for these measurements were also useful for evaluation of the distortion caused by the pulsing of the SIT vidicon and also for measurement of channel-to-channel crosstalk. 

The line images for the patterns obtained at the two pulse widths were distorted as was shown in Figure 3. However, the quality of the line images in the normalized difference pattern for 725 V (Figure 4c) were as good as those obtained for the unpulsed SIT vidicon. There is only a small amount of increased curvature at the minima on the side of the lines away from the center. The difference patterns for 700 and 750 V (not shown) were more rounded at the minima between the lines, but careful examination provided no improved criteria for their use in determining the optimum focus voltage. 

It should be emphasized that these plots represent the combined distortion caused by the camera lens and the SIT vidicon. 

For some experiments only the 6.7 to 7.2 cm region of the cell is actually used. Thus a 10 ysec pulse pattern was obtained with the vidicon moved a distance corresponding to 125 channels, so as to place its center over the region of interest. The plot of deviation vs. channel number, for this image, was the same as that obtained for the centered image, indicating that the distortion arose entirely from the SIT vidicon. 

Channel-to-Channel Crosstalk. In one of the brochures supplied by the manufacturer of the OMA the channel-to-channel crosstalk for the SIT vidicon is stated in these terms with a 10 ym line centered on a channel, more than 60% of the signal amplitude is centered in that channel and more than 98% of the signal is in that channel and the two adjacent channels. Some of the patterns obtained from the ruled disk studies were examined to see if they were suitable for the measurement of crosstalk. 

The lines on the ruled disk are 80 ym wide in the radial direction at the plane of the SIT vidicon faceplate, they are reduced to half that width, or about 40 ym. The width of an OMA channel element is 25 ym. Thus one can make an estimate of crosstalk by centering a line between two channels. The relative intensities for such a line are normalized so that the sum has a value of 2. The normalized relative intensity for one of the center channels is fg + f for the next three channels it is fl + f2> f2 + f3> and f3, respectively, where fg refers to the fraction of signal in the center channel, and fi, f , and f3 are the fractions for the successive channels on both sides. The sum, f0 + 2(f] + f + 3) should be 1. 

We are baffled as to the cause of the discrepancy between the calculated and measured intensity curves. The mathematics of the calculated curve needs to be refined to include the width of the slit above the rotor, which we had assumed to be negligible. Perhaps the effect of changing the slit width and the focus plane in the cell should be examined. Based on the good results obtained from sedimentation equilibrium experiments, we believe that the SIT vidicon, MIA electronics, and our software controlling the gathering of data are all behaving properly, but perhaps there are still problems to be solved. 

In general, we are satisfied with the performance of our OMA-based light detector system for the absorption optical system in the ultracentrifuge. Many of the problems that we had to solve were inherent in the optical system and the cells, but were hidden to users with photomultiplier detector systems. Other problems associated with the SIT vidicon have been satisfactorily solved. 

The interfacing of GC with MI fluorescence spectrometry also has been accomplished for fluorometric examination of GC effluents, the conventional photomultiplier tube detector is replaced by a SIT vidicon to facilitate rapid acquisition of MI fluorescence spectra of individual GC fractions (30). 

Fig. 89. Spectra of ICP-OES recorded with an SIT vidicon for the case of water, a europium solution and a dissolved bastnaesite sample containing europium [335].

Silicon Intensified Target (SIT) Vidicon and Intensified SIT (ISIT)... 

In this paper we briefly discuss the operation of the silicon intensified target (SIT) vidicon, describing what we conclude to be the spectroscopically most important properties of the detector. We provide experimental evaluation of the SIT vidicon characteristics including two-dimensional image fidelity channel-to-channel and pixel-to-pixel response as a function of position on the detector and temporal resolution and gating. We illustrate how these unique properties enhance our ability to make spectroscopic measurements while at the same time impose limitations on the use of the SIT vidicon. 

We describe a variety of experiments which employed an SIT vidicon detection system for atomic spectroscopy with various degrees of spatial and temporal resolution. 

The silicon intensified target (SIT) vidicon has a number of unique properties which make it a valuable detector for atomic spectroscopy. The SIT vidicon provides two-dimensional photoelectric detection with high sensitivity and rapid signal readout. Time resolution can be obtained in a time-resolved (real time) mode on the millisecond scale and in a time-gated (equivalent time) mode on the submicrosecond scale. 

Coupling an SIT vidicon detector with an on-line computer for detector control, experiment synchronization, data acquisition and data processing results in a powerful and flexible detection system. The flexibility results from the... 

---