Picosecond lasers streak camera detection

Figure 1. Diagram of apparatus for picosecond fluorescence studies using streak camera detection. A laser oscillator B dye cell C output reflector D polarizer E spark gap F KDP pockels cell G polarizer (crossed with D) H clear glass beamsplitter J laser amplifier K pin photodiode L transient digitizer M,N 1054 nm reflectors P 2nd harmonic generator Q 3rd or 4th harmonic generator R spectrograph S streak camera T biplanar photodiode U image...

The commercially available laser source is a mode-locked argon-ion laser synchronously pumping a cavity-dumped dye laser. This laser system produces tunable light pulses, each pulse with a time duration of about 10 picoseconds, and with pulse repetition rates up to 80 million laser pulses/second. The laser pulses are used to excite the sample under study and the resulting sample fluorescence is spectrally dispersed through a monochromator and detected by a fast photomultiplier tube (or in some cases a streak camera (h.)) ... 

As described above, recent advances in accelerator technology have enabled the production of very short electron pulses for the study of radiation-induced reaction kinetics. Typically, digitizer-based optical absorbance or conductivity methods are used to follow reactions by pulse radiolysis (Chap. 4). However, the time resolution afforded by picosecond accelerators exceeds the capability of real-time detection systems based on photodetectors (photomultiplier tubes, photodiodes, biplanar phototubes, etc.) and high-bandwidth oscilloscopes (Fig. 8). Faster experiments use streak cameras or various methods that use optical delay to encode high temporal resolution, taking advantage of the picosecond-synchronized laser beams that are available in photocathode accelerator installations. 

The nanosecond-picosecond two-color two-laser flash photolysis method is also useful to study the excited state of radicals, that is, the D, state. We applied nanosecond-picosecond two-color two-laser flash photolysis to detect the absorption and fluorescence spectra of the ketyl radical of benzophenone and its derivatives (BPH and BPDH ) in the excited state in the UV-visible region [111], since BPH and BPDH are well investigated radicals in various fields. Since BPH and BPDH are generated from irreversible ways, such as photoionization, we employed a streak camera to realize the single-shot detection of these intermediates. 

When the generation of picosecond laser pulses first became possible in the laboratory, methods of electronic detection which currently are in such widespread use for measurements performed on the picosecond time scale, e.g. streak cameras and two-dimensional photodiode arrays, were not readily available to the experimenter. Techniques had to be developed not only to measure accurately the kinetics of photoinitiated events which occur on this ultrashort time scale, but more importantly to monitor the width and shape of the laser pulse to ensure reliable and reproducible generation of these pulses. 

Another example of the use of optical multichannel detection is the picosecond spectroscopic study of acridine, s-tetrazine, and rhodamine B by Barbara et. al.(26) In this type of study, a sample containing the compound of interest is placed in the path of an A,6-ps FWHM laser pulse. The laser pulse is focused onto the sample cell, and the emitted light is collected and directed, by an assembly of lenses, into a streak camera which is capable of time-resolving the emission. Processing and analysis of the streak camera data are accomplished by means of an assembly consisting of a two-dimensional photodiode array... 

Transition radiation is considerably weaker than Cerenkov radiation, however since it is a surface phenomenon it avoids problems with radiator thickness and reflections inherent to Cerenkov-generating silica plates. Optical TR can be measured using a streak camera. An optical TR system has been used to time-resolve the energy spread of an electron macropulse in a free-electron laser facility [10]. Interferometry of coherent, far-infrared TR has been used to measure picosecond electron pulse widths and detect satellite pulses at the UCLA Satumus photoinjector, using charges on the order of 100 pC [11],... 

In the future, we can expect the ratho expensive picosecond dye lasers and Ti sapphire lasexs to be t laced by sin ler and less eiq>ensive device. A diode-punq>ed Nd YAG laser has already been used fw Ume-resolved detection in capillary zone eleftto(4ioresis, and one can purchase a streak camera with apulsed lasCT diode excitation source. Laser diodes have also been used as the excitation source for FD fluwiMnctry. The wavelengths are usually limited to 600-700 nm, but some laso diodes can be frequency-doubled to 410 nm. It is also likely that... 

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