Oscillation Period

Screenshot of the third iRHEED screen, the oscillation period module, showing the successful fit to a synthetically generated signal with strong variations of the amplitude and median of the data and the buttons to access the various functions of this module

The oscillation period module implements a unique, newly developed algorithm to accurately determine the period and phase of RHEED intensity oscillations. You graphically determine the onset of growth and estimate the oscillation period using the shaded area, with which the algorithm performs a running average to determine the median of the raw signal (black curve). The raw data is subtracted from this median, making it symmetric to zero. Similarly, the envolope (amplitude decay) is calculated, and the symmetric data is divided by this envelope to produce a trace that is symmetric to zero and has no decay.

Cosine fits to these preprocessed data are very accurate and reliable. The algorithm graphically displays the fit results. You may set a trigger by specifying a given number of oscillations (here 40), at which the algorithm gives you a signal to e.g. close the shutter. The phase of the oscillations becomes irrelevant as the algorithm measures the period and calculates the time at which a given number of oscillations have been completed, from the zero line position that you define.