Flash photolysis technique is used to measure the changes of the sample absorption caused by excitation of the sample with a short (nanoseconds) pulse of light.
Flash Photolysis instrument
A general scheme of the Flash Photolysis method is presented in Fig. 1. The main components used in the instrument are
pulsed laser system from Solar TII containing
- Nd:YAG laser LF117 with second harmonic generating (SHG) crystal,
- third harmonic generating crystal,
- Ti:Sapphire laser CF125 with SHG,
- parametric laser COPO2200;
- 450W Oriel Simplicity 66355 illuminator (Newport) with 6266 Xe lamp;
- control system mLFP (LuzChem) containing monochromator Digikröm CM110 and photomultiplying tube R7400U-20 (Hamamatsu);
- TDS3000B Digital Oscilloscope (Tektronix).
The instrument is controlled by a computer.
Fig. 1. Flash Photolysis instrument.
Main characteristics of the Flash Photolysis instrument
|Time resolution||30 ns|
|Excitation spectral range||350-440 nm, 700-890 nm|
|Excitation pulse energy||1 - 100 mJ|
|Excitation pulse duration||15 ns|
|Probing spectral range||300-850 nm|
|Probing spectral resolution||5 nm|
|Time per point||0.2 ns|
|Sensitivity (noise level)||0.001 OD|
Flash Photolysis technique is used to determine which intermediate states the excited sample goes through.
Usual Flash Photolysis technique is not sensitive enough for samples with only one monolayer of molecules. In Total Internal Reflection Mode (Fig. 2) the probing beam is reflected from a monolayer 20...100 times increasing accordingly the sensitivity.
Fig. 2. Flash Photolysis in Total Internal Reflection Mode.