In this paper, we propose technical solutions to solve the issue of the thermal stabilization of a room-temperature high-Q whispering gallery mode microwave sapphire resonator. This technology enables the design of very low phase noise microwave sources which can be used as references for phase noise measurements or for high sensitivity radar systems. Nevertheless, the sapphire resonator presents at the ambient temperature a high sensitivity to thermal fluctuations of the order of −70ppm∕K limiting the oscillator stability in the long term. An original resonator thermal configuration has been designed and optimized thanks to finite difference technique simulations. The symmetry of the proposed thermal structure increases the temperature control efficiency. Coupled to a high-resolution electronic temperature controller directly embedded on the microwave cavity, this structure presents a very low sensitivity to the environment thermal fluctuations. This sensitivity is better than −0.05ppm∕K.

Vapor cell atomic clocks are widely appreciated for their excellent short-term fractional frequency stability and their compactness. However, they are known to suffer on medium and long time scales from significant frequency instabilities, generally attributed to light-induced frequency shift effects. In order to tackle this limitation, we investigate the application of the recently proposed auto-balanced Ramsey (ABR) interrogation protocol onto a pulsed hot vapor Cs cell clock based on coherent population trapping (CPT). We demonstrate that the ABR protocol, developed initially to probe the one-photon resonance of quantum optical clocks, can be successfully applied to a two-photon CPT resonance. The applied method, based on the alternation of two successive Ramsey-CPT sequences with unequal free-evolution times and the subsequent management of two interconnected phase and frequency servo loops, is found to allow a relevant reduction of the clock frequency sensitivity to laser power variations. This original ABR-CPT approach, combined with the implementation of advanced electronics laser power stabilization systems, yields the demonstration of a CPT-based Cs cell clock with a short-term fractional frequency stability at the level of 3.1 × 10 −13 τ −1/2 , averaging down to the level of 6 ×10 −15 at 2000 s integration time. These encouraging performances demonstrate that the use of the ABR interrogation protocol is a promising option towards the development of low drift CPT-based frequency standards. Such clocks could be attractive candidates in numerous applications including next-generation satellite-based navigation systems, secure communications, instrumentation or defense systems.