A PSEUDORANDOM PINK NOISE FOR THE COMPUTER-BASED MEASUREMENTS OF LINEAR RESPONSES

We propose a nonbinary pseudorandom sequence for the measurement of li near responses. Compared with a maximal length shift register sequence (m sequence), this sequence is more suitable for digital processing b ased on computers; with the use of discrete Fourier transforms, the re sponse functions are reproduced without approximations from digitally sampled data because thp input power spectrum is pink, i.e., completel y flat in a given frequency range and 0 otherwise. In practice, the ne w sequence is simply the sum of harmonics with arbitrary phases and is produced readily with digital wave form generators. For reducing the peak power of this sequence, the amplitude distribution is better to b e bimodal rather than Gaussian. For demonstrating its feasibility with common digital hardware, the magnetic resonance of Rb atoms in a sub- MHz region was measured successfully. With the use of the fast Fourier transform algorithm, our software task was only 0.4% of that for the cross-correlational calculation based on an m sequence. (C) 1998 Ameri can Institute of Physics. [S0034-6748(98)01107-1].