We present a theory of the multi-threshold second-order phase transition,and experimentally demonstrate the multi-threshold secondorder phase transition phenomenon.With carefully selected parameters,in an external cavity diode laser system,we observe secondorder phase transition with multiple(three or four) thresholds in the measured power-current-temperature three dimensional phase diagram.Such controlled death and revival of second-order phase transition sheds new insight into the nature of ubiquitous secondorder phase transition.Our theory and experiment show that the single threshold second-order phase transition is only a special case of the more general multi-threshold second-order phase transition,which is an even richer phenomenon.
We demonstrate a narrowband optical filter which operates on the 52S1/2 to 52P3/2 transition at 780 nm in rubidium vapor based on optical-pumping-induced dichroism combined with Faraday anomalous dispersion effects. Its peak transmission is 18.4（2）% at the 52S1/2, F = 2 to 5^2P3/2, F＇ = 1, 3 crossover transition, whereas at the 5^2S1/2, F = 2 to 5^2P3/2, F＇ = 2, 3 crossover transition the transmission is 18.6（2）%. Both transitions have a bandwidth （full-width at half-maximum of peak transmission） as narrow as 24.5（8） MHz, which is remarkably improved compared with the narrowest bandwidth as we know. This technique can also be applied to other alkali atoms. OCIS codes： 120.2440, 230.2240, 300.6460. doi： 10.3788/COL201412.101204.
The population ratio between the excited states of rubidium in the electrodeless discharge rubidium vapour lamp is calculated according to the near-infrared spectra in the region of 780-1550 nm. By using a 1529 nm laser, we measure the density of natural rubidium atoms at the 5P3/2 level. The populations of different excited states are then clarified.
In order to realize laser frequency stabilization,the global evolution of an analyzer angle on the electrodeless-discharge-vaporlamp-based excited-state Faraday anomalous dispersion optical filter(LESFADOF)with a single transmission peak operating on the Rb1529 nm(5P3/2-4D5/2)is presented.We find that the transmission of the line center peak at 80°arrives at 14%in a 3 cm length lamp contained natural Rb mixed with 2 torr Xe buffer gas operating at 250°C with 176 MHz radio frequency.When it is used to realize laser frequency stabilization,the LESFADOF at near 80°is appropriate.Whether a single transmission peak or double transmission peaks depend on the rf voltage when two polarizers are crossed.
TAO ZhiMingWANG YanFeiHONG YeLongWANG DongYingZHUANG WeiCHEN JingBiao
Active optical clock,a new conception of atomic clock,has been proposed recently.In this work,we propose a scheme of active optical clock based on four-level quantum system.The final accuracy and stability of two-level quantum system are limited by second-order Doppler shift of thermal atomic beam.To three-level quantum system,they are mainly limited by light shift of pumping laser field.These limitations can be avoided effectively by applying the scheme proposed here.Rubidium atom four-level quantum system,as a typical example,is discussed.The population inversion between 6S 1/2 and 5P 3/2 states can be built up at a time scale of 10-6 s.With the mechanism of active optical clock,in which the cavity mode linewidth is much wider than that of the laser gain profile,it can output a laser with quantum-limited linewidth narrower than 1 Hz in theory.An experimental configuration is designed to realize this active optical clock.
We demonstrate experimentally the population inversion between 7S1/2 and 6P3/2 levels of cesium in thermal cesium cell with a 455.5 nm pumping laser.We calculate the relative population probabilities at each level theoretically with the density matrix method.In a steady state,5.8% atoms are at 7S1/2 level and 2.9% at 6P3/2 level,which builds up the population inversion between the two levels.We obtain the fluorescence spectra produced in thermal cesium cell in our experiment.The measured relative intensity of each available fluorescence spectral line in the experiment agrees very well with the theoretical result.The demonstrated population inversion between 7S1/2 and 6P3/2 levels can be used to construct an active optical clock of four-level system with a wavelength of 1469.9 nm.
WANG YanFeiWANG DongYingZHANG TongGangHONG YeLongZHANG ShengNanTAO ZhiMingXIE XiaoPengCHEN JingBiao
The intensity of fluorescence spectral lines of Rb atoms in the region of 350-1110nm is measured in eletrodeless discharge lamp. The population ratio between the excited states is calculated according to the spontaneous transition probabilities with rate equations. At the same time, the population density of energy level is also obtained. The results provide the potential applications of electrodeless discharge lamp in atomic filter and optical frequency reference at higher excited states without a pumping laser.
TAO ZhiMingWANG YanFeiHONG YeLongWANG DongYingZHANG ShengNanZHUANG WeiCHEN JingBiao
