Soft Report - Dipartimento di Fisica - Sapienza

Photo-Correlation Laboratories – UdR RomaConventional Photon Correlation Spectroscopyset-up (PCS). A He-Ne laser (λ=632.8 nm) of 10mW is focused on the centre of a vat mounted on agoniometer. The temperature of the sample, sit inthe centre of the vat, is controlled by a cooler-heater(HAAKE K35). The scattered light is focused,selected by a pinhole and revealed by a multimodefiber and a photomultiplier detector. A commercialALV-5000 logarithmic correlator computes theautocorrelation functions. Measurements can beperformed at various scattering vectors q (movingthe collecting arm and so varying the collectingangle) and in a correlation time window between 1µs and 10 s.Advanced photon correlation spectroscopyset-up. A He-Ne laser (λ=632.8 nm) of 35 mW issent on a polarizing maintaining single mode fiberand is focused on the centre of a vat mounted on agoniometer. The temperature of the sample, sit inthe centre of the vat, is controlled by a coolerheater(HAAKE FUZZYSTARC35). The scattered lightis collected by a single mode fiber. The photocountsare analysed by an home made software thatprovides a logarithmic correlation of the data. Formore details see the article "Software Toolkit for theStatistical Analysis of Photocounts". By means ofthe use of single mode fiber the coherence factor βreaches the ideal value of 1 and thereforeautocorrelation functions with a very high signal tonoise ratio are obtained. Measurements at variousscattering vector q (varying the collecting angle)and in a time correlation window between 1 µs and2 s can be measured.Infra Red Photon Correlation Spectroscopy (IR-PCS) set-up formeasurement of time correlation functions in non transparent/opalescentsystems. An IR (λ = 1064 nm) diode-pumped lasers is focused (lens L1in the picture) on the sample. The scattered signal can be collected atdifferent scattering angles - thus allowing to vary the momentumtransfer- through an appropriate slab-shaped window. A lens-collimatorsystem, couples the scattered intensity with an optical fiber connected toa silicon avalanche photodiode detector with 2% quantum efficiency and50c/s dark counts. The number of photon counts in a given time is thenrecorded and time-autocorrelation function is computed by a specificallydeveloped software. Several time decades are accessible with thistechnique, from few µs to 100s, while accessible exchanged momentarange from 10 4 to 10 5 cm -1 . The sample-holder cell is equipped with anheater and a temperature control device and is capable of reaching up to800K with an accuracy better than 0.1K, an essential feature for theinvestigation of cooperative and diffusive dynamics of supercooledliquids and glassy systems, as well as of macromolecular and latexnanospheres solutions.23SOFT Scientific Report 2004-06