Sydor ROSS 5800 Systems are offered with a dynamic calibration featured called DynaCal that corrects for both the geometric distortions of the system as well as the nonlinearities in the ramps. The calibration is performed for each ramp speed. This internal module enables remote calibration to be performed prior to data collection.
Dynamic Geometric Calibration (DynaCal)
On systems with DynaCal, the slow sweep geometric distortion is replaced with a swept image that maps out the dynamic distortions. The DynaCal head takes light pulses from the internal comb generator and splits the signal into ~ 11 spatially separated points. For each sweep speed, a swept image is taken, and the resulting grid of points image is used for calculating the geometric distortion. On systems with a DynaCal head, this supercedes the slow swept geometric distortion calibration.
Time-Base Calibration (TimeCal)
Streak speed calibrations are obtained with the use of the internal comb generator. The comb generator is then split into an array of points across the photocathode. It is important to calibrate the streak speed at all spatial locations in the image since it can vary by more than 1% due to the fringing fields at the edges of the deflection plates.
The image above is a cartoon of how the calibration is generated. A grid of points is generated using an internal comb generator which is spread out to an array of vertical points and creates a row of horizontal points in time. The red dots are representative of a dramatically distorted raw image. In this example, the blue arrow shows the geometric distortions, the blue dashed is the nonlinear ramp distortion. In the corners, you see a combination of both types of distortions.
With DynaCal correction, most of these distortions are removed. It does this with the 3rd order 2D polynomial fit. The results can be seen in the center image.
TimeCal correction takes the calibration one step further, removing any ramp nonlinearities that the 3rd order correction couldn’t account for. This correction takes the middle row of points and assumes that the previous correction has adequately straightened the data in the vertical direction. TimeCal then takes the known comb frequency to calibrate the time axis and calculates the remaining nonlinearities on the time axis.
The two corrections, DynaCal and TimeCal, work together to provide a more fully corrected image. The second step also utilizes the known comb frequency to provide time base calibration. Data is shown in the first two images as pixels, however data is represented in the horizontal axis in real-time for the TimeCal & DynaCal corrected example. The calibration file generated using this process can be applied to any future image.
When the ROSS 5800 with DynaCal is purchased, both Dynacal and TimeCal are included.