A Set Of Instruments For Measuring Parameters Of Single Subnano- And Picosecond Signals

Abstract

Present -day experimental physics and laser technology set forth increasingly high requirements to fast process parameters measuring means. Some 10 or 15 years ago, investigations were focused on processes of a nanosecond duration (10 -9 s), whereas today research demand measurements in pico (10 -12) and femtosecond (10 -1s s) time ranges.Most vital now are complex studies, i.e. those dealing not only with the process itself, but also with associated secondary phenomena, often quite diverse in physical nature.During the last years much attention was paid, for instance, to design and investigation of lasers capable of generating ultrashort pulses 1, 2 lasting fractions of a nanosecond. In such lasers, the radiator outputs a train of ultrashort pulses of variable intensity with a constant interpulse period which is a function of the resonator length. Such lasers are employed in various systems.Technical implementation and study of such systems demand, first of all, that credible information be available to the researcher on the time development of the process in various parts of the system, deformations of signals passing its different elements, etc. Besides, the interactions between the laser ultrashort pulse train and the substance should be studied in time, with regard for their correlation with the initiating radiation.The greatest amount of information pertaining to such processes may be obtained with the help of the method of fast oscillography. The instrumentation used in this method should meet the following requirements: measurability of single -process parameters, multichannel design, precise cross -correlation of channels in time, and undistorted recording of signals of a picosecond range, and multipurpose nature. The structural diagrams of three -channel measuring installations meeting the above requirements are shown in Fig. 1, where 1 thru 3 are channel inputs; 4 thru 6, primary converters; 7 thru 9, oscillographic recorders (OR), and 10, sweep generator. Each OR may have its own sweep generator, but the use of a common sweep generator eliminates mutual instability of the recorders sweep. With due regard to time relationships between the processes under study, two versions of channel connection are possible: series connection for processes time -speced longer than the sweep duration (Fig. la) and parallel connection for simultaneous processes, i.e. those occuring within the sweep time (Fig. lb).Fig. 2 presents a detailed diagram of the LOTOS measuring system 3 featuring series -connected ORs. Sweep generators 5, 7 and 9, and illumination generators 6, 8 and 10 may be taken from the set of any available recorder. Time scale generator 4 is common for all the channels. 11 is the primary start -up converter. In a parallel OR design, a common sweep generator is used.The system may serve as a "time magnifier" in observing a process. For this purpose, the sweep of channel III is set at a maximum duration. After passing converter 1, the process reaches all the channels simultaneously. In channels I and II, fa...