Subhasis Panja

Saturated Absorption Spectroscopy (SAS) is a technique commonly used for recording Doppler broadening free absorption spectra of atomic vapours and also to estimate the natural linewidth of the atomic transitions. However, in conventional SAS two counter-propagating laser beams are used as pump and probe and the linewidths of the absorption spectra show strong dependences with the power of the laser beams following the saturation theory. The present work demonstrates a unique technique of Cross-Beam spectroscopy for recording saturated absorption spectra near their natural linewidth by deploying pump and probe beams in orthogonal orientation instead of their collinear position. In the case of orthogonal orientation, the recorded absorption linewidth hardly varies with the power variation of the laser beam and does not follow the Saturation theory. Following the above technique, transition frequencies for different isotopes of ytterbium (Yb) have been measured, and the transition frequency for the most abundant isotopes, i.e., Yb174, estimated to be 751526556.04(60) MHz with natural linewidth of 32.0(8) MHz.

White Rabbit (WR) is an optical fibre-based time-frequency synchronization technology typically used in timekeeping laboratories for distributing time-frequency signals from a reference clock to distant locations. The accuracy of the received signals at the user end can be affected by random noise processes present in the WR network due to the internal electronic components of WR devices. In this paper, we investigate the presence of random noise processes in the WR network. We then study their statistical properties and model the distribution based on experimentally recorded measurements. According to our study, the probability density function (PDF) follows a Gaussian mixture model (GMM) with varying distribution parameters, and the correlation analysis indicates a strong correlation of the phase noise process over the temporal samples. Furthermore, the developed phase noise models have also been verified by comparing them against additional experimental data. Finally, we present the methodology to generate the phase noise process using computer simulations with the PDF and correlation models developed in this work to help algorithm developers and equipment manufacturers make use of our results.

We report the frequency stabilization of an external cavity diode laser (ECDL) to a reference molecular iodine (I₂) transition at 13,531.18 cm⁻¹ (739.03382 nm). Using the Modulation Transfer Spectroscopy (MTS) method for the highly sensitive detection of weak absorption signals, the Doppler-free absorption peaks of I₂ corresponding to the hot band transition R(78) (1–11) are resolved. The ECDL’s frequency is stabilized with respect to one of the lines lying within the reference absorption band. For this, the iodine vapor cell is heated to 450 °C and the corresponding circularly polarized pump and probe beam powers are maintained at 10 mW and 1 mW, respectively, to avoid power broadening. The short (100 ms) and long-term (50 h) linewidths of the frequency stabilized laser are measured to be 0.75(3) MHz and 0.5(2) MHz, respectively, whereas the natural linewidth of the specific I₂-transitions lie within a range of tens of MHz.