Tham khảo tài liệu 'photodiodes communications bio sensings measurements and high energy part 7', kỹ thuật - công nghệ, cơ khí - chế tạo máy phục vụ nhu cầu học tập, nghiên cứu và làm việc hiệu quả | Single Shot Diagnostics of Quasi-Continuously Pumped Picosecond Lasers Using Fast Photodiode and Digital Oscilloscope 111 4. Experimental investigation of picosecond laser pulses Experimental determination of the measuring system minimal FWHM Minimal FWHM was determined experimentally using an experimental fiber laser generating mode-locked pulses at ym with duration less than 2ps measured by the autocorrelator . Pulse of this duration can be assumed as Dirac delta function for our measuring system. In order to avoid nonlinearities in the photodiode and oscilloscope during all the measurements the oscilloscope vertical resolution was set at 5mV div and the signal amplitude was about 20 mV. The oscilloscope bandwidth was set to maximal analogue bandwidth of 9 GHz with the sampling frequency of 40GS sec. The oscilloscope enables two regimes of waveform acquisition and display - linear only measured points are displayed and sin x x approximation by this function . It was experimentally found that the FWHM measurement difference using these two acquisition regimes is about 1 ps and can be neglected. Therefore most of further described measurements were performed in the linear acquisition regime. There are two possibilities how to determine the FWHM of the measured pulse. The first is use of build-in function of the oscilloscope - Width at 50 . The oscilloscope also enables to show histogram or statistics of these measured values. The second possibility is to save the data and perform a curve fit by Gaussian function. It has been found that using a Gaussian fit is for our pulses adequate and the determined FWHM of a such pulse with duration below 80 ps is about 18 shorter than the value measured by the oscilloscope. Because of this uncertainty most of FWHM values presented below were determined by the Gaussian fit of the measured pulse shape. All the presented values represent average value of about 100 pulses. Recorded pulse from the ym fiber laser with .
