Streak cameras are typically designed by a top-down concept. Top of the concept is the streak tube technology that is selected to obtain best measurement results for the application specific requirements. As streak tubes vary in physical dimensions and electrical characteristics, streak cameras are designed with different mechanical housings, tube polarisation electronics, sweep units and communication interfaces. This approach leads to a large number of individual and consequently expensive streak cameras. A new streak camera concept allows the integration of different streak tubes to offer more flexibility for specific application requirements but also general needs. The mechanical design provides interfaces for various sweep units, image intensifier units or electro-mechanical shutter devices. The concept supports a modular configuration using plug-in sweep units today only realised with standard streak cameras. Combined with standardised electrical interfaces, the streak camera can be configured for various applications without redesign. This additionally allows the adaptation to vacuum and other demanding environmental conditions.
The temporal resolution of a synchroscan streak camera is mainly limited by the intrinsic tube resolution, the laser pulse width and the synchronization jitter between the camera and the laser source. Studies show that laser phase noise is localised principally at low frequency. A previous system was designed in order to eliminate the very low frequency jitter. The system allows the streak camera to accumulate a signal during over a long period (several hours) without significant temporal resolution degradation. In order to work properly, this system use a laser reference directly coupled to the streak camera on the top of the photocathode. The localisation of this laser reference spot is locked at a predefined position and then, the temporal axis of the streak camera image is locked. To allow this control, the software changes the phase between the deflection plate voltage and the synchroscan signal. The resolution obtained was about 2 ps Full Width at Half Maximum (FWHM) which is the best resolution available in the accumulation mode and this can be achieved whatever the accumulation time. In this paper, we describe an upgrade of this system which uses the laser reference information to accumulate the different frames after a retiming. It calculates the centre of gravity (COG) of the laser reference, shifts the image on the temporal axis with a sub-pixel resolution to place this COG to a predefined position. Then the frames are accumulated. By this way, the inter frame jitter is reduced. This system benefits from the very high temporal resolution of the streak camera to make to correction so that it can be very efficient. In photon counting, the temporal resolution with this system is improved to a value of 1,5 ps FWHM. With a signal to noise ratio of about 1000 the acquisition time is 35 minutes.
Different temporal instabilities, which degrade the temporal resolution of s a synchroscan streak camera, have been studied. Each of the 3 main components: the laser, the trigger and the streak camera, have their intrinsic instability, thus a degradation of the final temporal resolution is occurred. An internal PLL in the streak camera has been developed in order to improve the temporal resolution. The synchroscan signal is used to lock the phase of the deflection voltage with the laser beam as close as possible. The phase detector has 0 to 360° area detection and a jitter lower than 300 fs FWHM integrated from 10 to 600 kHz, allowing sub picoseconds synchronization with the laser beam. The slow drifts, from 0 to 25 Hz, of the phase comparator are cancelled with a laser reference directly inserted in the camera input. By the way of an image processing, the phase command voltage is modified to lock the position of this laser reference. Results show that this stabilized camera can be used immediately after it is turned on (suppression of the warm-up time) and has very good temporal resolution, even with a long time exposure (2.4 ps FWHM with a time exposure of 2 hours has been realized). This allows more exploration in detection of very weak signals.
Video rate CCD cameras or high sensitivity slow scan CCD cameras are typically used today as streak camera readout systems. In most standard applications the output signal is processed in analog mode. Particularly low light level experiments can take advantage of the discrete nature of light by counting single photons. For these applications the output signal is analyzed in order to detect single events that are directly related to single photons. Therefore the streak camera is combined with a sensitive video rate CCD camera and a fast image processing system. The conversion and amplification stages inside the system are presented with their characteristics related to the photon counting application. Particularly their pulse height distribution and their spatial resolution are considered. Different image processing algorithms used to detect and spatially locate single events from the camera output signal are compared in terms of technical implementation and processing performance. The streak camera together with the readout camera and the image processing system are characterized for their detection quantum efficiency. The photon counting mode is compared to the analog mode and its advantages in terms of signal to noise ratio and spatial resolution is presented.