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--- howto:how_to_measure_the_instrument_response_function_irf [2016/12/06 12:05] – veiga
+++ howto:how_to_measure_the_instrument_response_function_irf [2019/11/04 09:45] – [Appropriate Count Rate for Measuring an IRF] buschmann
@@ Line 78: / Line 78: @@
 ===== Appropriate Count Rate for Measuring an IRF =====
 See [[glossary:Differential Count Rate]]
+===== How often does the IRF need to be measured? =====
+In spectrometers, the IRF is usually measured before or after each measurement.
+In microscopy-applications, this is usually not practical; and often it is sufficient to measure the IRF once during a measurement series, provided that the system has had time to warm up (~15min), and neither the repetition rate nor the intensity at the diode laser driver is changed (the current which drives the laser).
+If the intensity needs to be changed, the optical attenuation can be adapted.
+A special case are systems with 2-Photon-Excitation (2PE). Here, usually TiSa-lasers are used which have fs-pulses, therefore the IRF is normally determined by the detector. In these cases, often the IRF can be measured once (and the excitation wavelength is not important, provided that the IRF is measured with a quenched dye and the same filterset is used as for the sample), and re-used later. Over time or upon changes of the excitation wavelength, the position of the IRF can shift slightly, but this is accounted for with the "IRF-shift"-parameter of the fitting equation.
 ===== How to compensate IRF effects in the analysis of time domain measurements =====