Long pass filters

The main problem has been a methodological one. The patch clamp analysis of single channels views the world of channels through a very small analytical window [10]. A single channel event (opening) needs to be sufficiently long-lived and sufficiently large to be picked up within the current noise band under optimized conditions, and with the low-pass filter set to say 2 kHz. The open time needs to be close to a millisecond and the current amplitude close to 0.5 pA to permit detection. 

The dye laser irradiates an external cell which contains 40 Pa (0.3 torr) Io vapor. A 1P28 photomultiplier whose face is covered by a 610 nm long pass filter measures the 12 fluorescence, while a photodiode monitors a reflected spot of the dye laser. The ratio of fluorescence to dye laser power is displayed on a strip chart recorder. The si dearm temperature is gradually (1-2 hours) raised from about 210 K or 220 K, where fluorescence in the external cell is strong, to whatever temperature is required to reduce the signal by about 60%. 

To dry the filter, two halogen heat-emitters are installed above the filter. The filter, if wet, causes the air flow to decrease. The air flow rate has a range from 90 to 550 m h . The air flow is forced by the fan which gives Ap = 4000 Pa. The filtered air is ejected off the station by the 2 m long outlet tube. The aerosol sampling station ASS-500 components are shown in Fig. 9.12. 

One additional technique, which is directly related to PM, is the PA excitation (PAE) spectrum [36J. In this technique the wavelength of the excitation source is continuously changed while the intensity of a particular PA band in the PM spectrum is monitored. This is readily done using a powerful xenon lamp coupled to a monochromator equipped with several long- and short-pass filter combinations. The PAE spectra are usually used for studying the excited electronic states of the polymer samples rather than the photoexcitations themselves (361. They can yield information, for example, on the location of the lowest allowed exciton (l u), the continuum threshold, and other important electronic states above it. This complementary information is useful in relation to PL and its excitation spectrum. 

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