Atish Roy

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.

We describe an improved laser frequency stabilization technique that overcomes limitation of the conventional Transfer Cavity (TC) method by prohibiting frequency drift of the desired (working) laser arising due to change in differential optical path length of the Fabry-Perot (FP) cavity with respect to the reference laser. Unlike the TC where noise at each stage propagates and cascades to the working laser, in this novel “Loop Stabilized Transfer Cavity (LSTC)” technique, different stages like the reference and working lasers, FP cavity constitute a loop which is stabilized altogether rather than stabilizing the individual component. As a result, frequency of the working laser is restricted from drifting and overall noise is also reduced as compared to that in the TC. Theoretical and experimental results comparing both the techniques are presented here.

Phase-stabilized distribution of radiofrequency (RF) signal is an essential requirement for many modern technological applications and advanced scientific experiments including clock synchronization or synchronization of distributed sensors. Coaxial cables are commonly used for the distribution of RF signal but the phase of the RF signals is very much sensitive to the variation of ambient conditions, especially temperature variation. In this letter, we introduced a technique and verified with 10 MHz signal for real-time measurement of phase-drift due to varying ambient condition along with phase-stabilized RF signal transmission through the coaxial cables by active phase compensation.

Precise transfer of time and frequency signals over long distances as well as clock synchronization to an ultra‐stable reference are very crucial for many of the technological applications as well as for advanced scientific research. These reinforces a wide range of applications such as navigation, power grid management, mobile communication, and so on. In order to compare the performances of two highly stable and accurate atomic clocks, it is desirable that the link between the two clocks, that is, the transmission link has higher level of stability than those clocks. This article describes establishment of an ultra‐stable optical fiber link employing White Rabbit network for transfer of time and frequency signals and also for comparing performance of atomic clocks. Utilizing this link, time signals have been transferred within an uncertainty of ±130 ps at ambient temperature (30°C–40°C) and the instability of the link in terms of modified Allan‐deviation reaches to ∼10⁻¹⁶ within one day of integration time.

Nearly collimated atomic beam is of interest for a variety of experiments. This article reports a simple way of modifying the atomic beam distribution using a dark wall oven and describes detailed study of outcoming atoms’ spatial distribution. A simple design is obtained by employing the fact that inhomogeneous thermal distribution along a capillary results due to its partial resistive heating. Based on this phenomenon, we have designed a dark wall oven consisting of a reservoir, collimator, and cold absorber at the exit end of atoms, where all three are fabricated out of a single stainless steel capillary. The nearly collimated spatial distribution of the atoms resulting due to the absorber eliminating the atoms diverging above a certain angle is modeled and experimentally verified. A divergence as minimum as 1.2(1)° corresponding to a half angle θ_1/2 = 0.9(1)° is measured at an oven temperature of 250 °C that produces an atomic flux of about 8 × 10⁹ atoms s⁻¹. Total flux as estimated using our measured spatial distribution of atoms matches well with the numerically simulated values of it for the dark wall oven.

We present precise values of the dipole polarizabilities ( α ) of the ground [ 4 f 14 6 s ] 2 S 1 / 2 and metastable [ 4 f 14 5 d ] 2 D 3 / 2 states of Yb ⁺ , that are important in reducing systematics in the clock frequency of the [ 4 f 14 6 s ] 2 S 1 / 2 → [ 4 f 14 5 d ] 2 D 3 / 2 transition. The static values of α for the ground and [ 4 f 14 5 d ] 2 D 3 / 2 states are estimated to be 9.8 ( 1 ) × 10 − 40 J m 2 V − 2 and 17.6 ( 5 ) × 10 − 40 J m 2 V − 2 , respectively, while the tensor contribution to the [ 4 f 14 5 d ] 2 D 3 / 2 state as − 12.3 ( 3 ) × 10 − 40 J m 2 V − 2 compared to the experimental value − 13.6 ( 22 ) × 10 − 40 J m 2 V − 2 . This corresponds to the differential scalar polarizability value of the above transition as −7.8(5) × 10 − 40 J m 2 V − 2 in contrast to the available experimental value −6.9(1.4) × 10 − 40 J m ² V ⁻² . This results in the black-body radiation shift of the clock transition as − 0.44 ( 3 ) Hz at the room temperature, which is large as compared to the previously estimated values. Using the dynamic α values, we report the tune-out and magic wavelengths that could be of interest to subdue systematics due to the Stark shifts and for constructing lattice optical clock using Yb ⁺ .