Soft Report - Dipartimento di Fisica - Sapienza
Soft Report - Dipartimento di Fisica - Sapienza
Soft Report - Dipartimento di Fisica - Sapienza
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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 "<strong>Soft</strong>ware 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) <strong>di</strong>ode-pumped lasers is focused (lens L1in the picture) on the sample. The scattered signal can be collected at<strong>di</strong>fferent 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 photo<strong>di</strong>ode 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 <strong>di</strong>ffusive dynamics of supercooledliquids and glassy systems, as well as of macromolecular and latexnanospheres solutions.23SOFT Scientific <strong>Report</strong> 2004-06