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We present experimental results on the sub-Doppler Rydberg spectroscopy of potassium in a hot cell and cold atoms, using two counterpropagating laser beams of 405 and 980 nm as an inverted ladder-type excitation configuration (4S 1/2-5P 3/2-nS 1/2 and nD 3/2,5/2). Such an inverted ladder-type scheme is predicted to be without the sub-Doppler electromagnetically induced transparency feature in a thermal ensemble under the weak-probe approximation. Instead, we utilize a strong probe field and successfully observe a transparency window with a width narrower than 50 MHz. Our all-order numerical simulation is in satisfactory agreement with the experimental results. This narrow linewidth allows us to measure the energy levels of the Rydberg levels from n = 20-70 with improved accuracy. The deduced ionization energy agrees with the previous measurements. Furthermore, the two-photon Rydberg excitation scheme was applied to the cold ensembles to study the ground-state atoms population decrease in the magneto-optical trap for various Rydberg states. Our experimental observations suggested two distinct regimes of the trap losses under different probe detuning conditions. While the far off-resonance case (p 0) can be described by the picture of dressed atom, the on-resonance case (p ∼ 0) reveals more interesting results. The higher Rydberg states suffer larger trap loss. Besides, even with similar level energies, the excitation to nD states result in faster escape of the ground-state atom from trap than nearby nS states.

We report absolute frequency measurements of molecular iodine P(46) 5-4 a, a, and a hyperfine transitions at 647 nm with a fiber-based frequency comb. The light source is based on a Littrow-type external-cavity diode laser. A frequency stability of 5×10 at a 200 s integration time is achieved when the light source is stabilized to the P(46) 5-4 a line. The pressure shift is determined to be -8.3(7)  kHz/Pa. Our determination of the line centers reached a precision of 21 kHz. The light source can serve as a reference laser for lithium spectroscopy (2S→3P).

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Doppler-free spectroscopy of 40Ca+ on the transition 3D3/2 → 4P1/2 known as the frequency standard for repumping beam of Calcium ion trap was performed by means of optogalvanic detection. This reference signal was applied to measure the frequency stability of laser locked to the resonance of an ultra-low expansion (ULE) glass made cavity. Lamb dip spectrum fitting of this Calcium ion spectra revealed that the long-term drift of our laser system is below 2 MHz per hour. A simple setup for frequency locking of dual colour of lasers at 866 nm and 780 nm was also demonstrated. Consistencies of the frequency difference between these two lasers were measured less than 2 MHz in a hour after stabilizing both lasers to the cavity.