Specifications

Chapter 5 Timing Modes 47
periodic. The timing of the External Sync pulse is entirely at the user’s discretion. In
Figure 19, the External Sync pulse is shown arriving after the read. Detection of the
External Sync pulse enables a new readout to occur on completion t
exp
+ t
c.
SCAN
Shutter
Monitor
External Sync
(negative polarity shown)
t
exp
t
w1
t
R
t
c
cleans
acquisition
t
R
t
R
t
R
t
R
actual exposure time
Figure 18. Frame Transfer where t
w1 +
t
exp
+ t
c
> t
R
External Sync
(negative polarity shown)
SCAN
Shutter
Monitor
t
w1
t
c
t
exp
cleans
acquisition
t
R
t
R
t
R
t
R
actual exposure time
Figure 19. Frame Transfer where pulse arrives after readout
Kinetics Mode
Kinetics mode uses the CCD to expose and store a limited number of images in rapid
succession. The time it takes to shift each line (or row) on the CCD is as short as a few
hundred nanoseconds to few microseconds, depending on the CCD. Therefore the time
between images can be as short as a few microseconds. Kinetics mode allows frame
transfer CCDs to take time-resolved images/spectra.
Note: Kinetics mode is an option, so the controller must be programmed before your
order is shipped. If the Kinetics option has been installed in the ST-133/ST-133A, this
readout mode will be made available when you select the appropriate camera type on the
Hardware Setup dialog box.
Below is a simplified illustration of kinetics mode. Returning to our 4 × 6 CCD example,
in this case 2/3 of the array is masked, either mechanically or optically. The shutter
opens to expose a 4 × 2 region. While the shutter remains open, charge is quickly shifted
just under the mask, and the exposure is repeated. After a third image is collected the
shutter is closed and the CCD is read out. Since the CCD can be read out slowly, very
high dynamic range is achieved. Shifting and readout are shown in Figure 20.