Double Resonance Optical Pumping Research Articles

Two-photon coherence in a DROP-FWM medium

In this work, we report experimental studies on coherence in a medium exhibiting DROP (Double Resonance Optical Pumping)-FWM (Four Wave Mixing). Here 5S1/2(F) → 5P3/2(F/) → 5D (F//) two photon transition of hot 87Rb atoms is used. The 5S→5P connection is modified by introducing an additional beam phase coupled to the original beam linking F = 2 → F/ transition. The frequency of the additional beam is offset from that of the original beam by ≈ +10Γ (Γ is natural linewidth). Such a two-beam configuration in F→F/ manifold effectively satisfies conditions of Vee (V) linkage or degenerate two-level connection (DTLC), depending on the detuning of the 780nm laser. This transformation profoundly affects the behavior of the ensuing Ladder (Ξ) system. While the (I) Ξ +V condition is favorable for Electromagnetically Induced Transparency (EIT), the (ii) Ξ + DTLC brings in the effect of Electromagnetically Induced Absorption (EIA). The EIT-dominated situation is helpful for FWM to take place, and the EIA effect augments the stronger presence of DROP. This condition is verified by monitoring the blue fluorescence emanating from the 5D→6P3/2→5S1/2 decay route. The DROP effect follows the Amplified Spontaneous Emission (ASE) pattern in the media. The origin of blue photons is also due to FWM under EIT conditions. In the case of EIA, the dominant condition increment in blue fluorescence is due to increased stimulated emission. The blue photons mainly contributed by (i) FWM and (ii) increased participation of stimulated emission are directional in nature and phase coherent.

Optical-optical double resonance spectroscopy of Rb 5D3/2,5/2 in magnetic fields

We have investigated the optical-optical double resonance (OODR) spectroscopy of 87Rb for transition 5S1/2 → 5P3/2 → 5D3/2,5/2 in magnetic fields. Unlike the electromagnetically induced transparency (EIT) spectroscopy of the transition to high Rydberg states (Opt Express, 25(2017)33575), the spectral observation to this low excited state remains much discrepancy compared to the theory simulation as the strong coupling between 5P3/2 and 5D3/2,5/2 leads to a state-dependent spectral broadening due to double resonance optical pumping (DROP) effect. Instead, the OODR method employs a weak optical coupling between these two states, serving as probe, where the spectral broadening can be ignored. We experimentally record the Zeeman-splitting spectrum of 87Rb to 5D3/2 and 5D5/2 in magnetic fields by OODR and the observed spectra are well in accordance with the theoretical calculation. It shows OODR is more suitable to investigate the high resolution spectroscopy of the excited state when the relaxation in DROP can't be neglected.

High resolution spectroscopy of Rb in magnetic field by far-detuning electromagnetically induced transparency

We have presented a high resolution spectroscopy of Rb in magnetic field by far-detuning electromagnetically induced transparency (EIT). The EIT spectrum in the Ξ-type configuration is usually companied by a double resonance optical pumping (DROP) due to the strong optical coupling between the two upper states, leading to the spectral lines seriously deformed and widely broadened for complex relaxation processes in DROP. Here we demonstrate a high resolution spectroscopy by far-detuning EIT for 87Rb 5S1/2 → 5P 3/2 → 5D 5/2 in magnetic fields. The method of far-detuning eliminates the relaxation in DROP to the most extent and decreases the spectral linewidth from more than 20 MHz down to its natural linewidth limit (6 MHz). The deformation of the spectral lines also disappears and the observed spectra are well in accordance with the theoretical calculation. Our work shows that far-detuning EIT is a reliable high resolution spectroscopic method when the relaxation in DROP cannot be neglected, especially for the case of transition to low excited states.

Doppler-broadened four-wave mixing under double-resonance optical pumping in the 5S1/2–5P3/2–4D5/2 transition of warm 87Rb atoms

We investigate stimulated four-wave mixing (FWM) in the 5S1/2–5P3/2–4D5/2 transition of warm 87Rb atoms. Here, the telecommunication wavelength (1529 nm) of the 5P3/2–4D5/2 transition is nearly twice that of the 5S1/2–5P3/2 transition (780 nm). The observed FWM signals of the 5P3/2–4D5/2 transition indicate that the FWM process is significantly influenced by the two-photon Doppler broadening due to the wavelength difference between both transitions and the double-resonance optical pumping (DROP) effect due to two-step excitation. We elucidate the suppression of the FWM process due to the DROP effect using a simple six-level atomic model.

Measuring the Hyperfine Splitting and Deriving the Hyperfine Interaction Constants of the Cesium 5p67d 2D5/2 Excited State

The measurement of the cesium (Cs) 5p67d2D5/2 excited state’s hyperfine splitting intervals and hyperfine interaction constants was experimentally investigated using a ladder-type (852 nm + 698 nm) three-level Cs system (5p66s2S1/2–5p66p2P3/2–5p67d2D5/2) with a room-temperature Cs atomic vapor cell. By scanning the 698 nm coupling laser’s frequency, the Doppler-free high-resolution electromagnetically-induced transparency (EIT)-assisted double-resonance optical pumping (DROP) spectra were demonstrated via transmission enhancement of the locked 852 nm probe laser. The EIT-assisted DROP spectra were employed to study the hyperfine splitting intervals for the Cs 5p67d2D5/2 excited state with a room-temperature Cs atomic vapor cell, and the radio-frequency modulation sideband of a waveguide-type electro-optic phase modulator (EOPM) was introduced for frequency calibration to improve the accuracy of frequency interval measurement. The existence of EIT makes the DROP spectral linewidth much narrower, and it is very helpful to significantly improve the spectroscopic resolution. Benefiting from the higher signal-to-noise ratio (SNR) and much better resolution of the EIT-assisted DROP spectra, the hyperfine splitting intervals between the hyperfine folds of (F” = 6), (F” = 5), and (F” = 4) of the Cs 5p67d2D5/2 state (HFS6″–5″ = −10.60(17) MHz and HFS5″–4″ = −8.54(15) MHz) were measured and, therefore, the magnetic dipole hyperfine interaction constant (A = −1.70(03) MHz) and the electrical quadrupole hyperfine interaction constant (B = −0.77(58) MHz) were derived for the Cs 5p67d2D5/2 state. These constants constitute an important reference value for an improvement of the precise measurement and determination of basic physical constants.

Laser frequency stabilization on 5P → 5D transition by double resonance optical pumping and two-photon transition spectroscopy in rubidium

We present a laser frequency locking scheme for the high excited transition of rubidium, which cannot be directly referenced by atomic absorption spectroscopy. Double resonance optical pumping spectroscopy and two-photon transition spectroscopy of a 5S → 5P → 5D transition are obtained in a room temperature vapor cell and employed as the reference sources. An Allan deviation of 1.71 × 10−12 at an averaging time of 2048 s with a residual frequency fluctuation of ±0.2 MHz over 7000 s is obtained by two-photon transition spectroscopy. The case of double resonance optical pumping spectroscopy presents an Allan deviation of 4.86 × 10−12 at an averaging time of 2048 s with a residual frequency fluctuation of ±0.4 MHz over 7000 s. One distinct advantage of two-photon transition spectroscopy method is demonstrated by the analysis of the fast Fourier transform of error signal. A narrower full width at half-maximum of two-photon transition spectroscopy and a higher zero crossing slope by using a frequency modulation method lead to a better frequency stabilization. This work provides a technical basis for the laser frequency stabilization based on atomic and molecular transition spectroscopy, and it also supplies a new frequency standard for optical telecommunication applications.

Experimental Study on Double Resonance Optical Pumping Spectroscopy in a Ladder-Type System of 87Rb Atoms**Supported by the National Key R&D Program of China under Grant No 2017YFA0304203, the National Natural Science Foundation of China under Grant Nos 61575116, 61705122, 61728502, 91736209 and 11434007, the Changjiang Scholars and Innovative Research Team in University of Ministry of Education of China under Grant

Double resonance optical pumping spectroscopy has an outstanding advantage of high signal-to-noise ratio, thus having potential applications in precision measurement. With the counter propagated 780 nm and 776 nm laser beams acting on a rubidium vapor cell, the high resolution spectrum of 5S1/2 − 5P3/2 − 5D5/2 ladder-type transition of 87Rb atoms is obtained by monitoring the population of the 5S1/2 ground state. The dependence of the spectroscopy lineshape on the probe and coupling fields are comprehensively studied in theory and experiment. This research is helpful for measurement of fundamental physical constants by high resolution spectroscopy.

The blue light in a ladder system: from double resonance optical pumping to Autler-Townes splitting

In this experimental work we report our findings about a Ladder (Ξ) transition 5S1∕2 → 5P3∕2 → 5D3∕2 of 85Rb atoms under different laser power combinations. Based on the ratio of power levels of two individual lasers, which are used in counter-propagating configuration, the system exhibits double resonance optical pumping and Autler-Townes splitting. The excursion of the Ξ level coupling is studied alongwith photon counting of blue light originating from 5D3∕2 → 6P3∕2 → 5S1∕2 non-degenerate decay. The blue photon statistics shows that emitted radiation are thermal. However the probability density of the integrated photon count vs. laser power exhibits a jump in intensity scale followed by a long tail, which resembles Levy type distribution. This may be considered as a signature when the level dressing changes in Ξ system as theoretically discussed earlier by Abi-Salloum [T.Y. Abi-Salloum, J. Mod. Opt. 57, 1366 (2010); T.Y. Abi-Salloum, Phys. Rev. A 81, 053836 (2010)].

Blue fluorescence as a frequency offset reference in the rubidium 5S-5P-5D transition.

In this work, we address the issue of the suitability of blue fluorescent light as a frequency offset reference during the ladder-level excitation 5S1/2→5P3/2→5D3/2 of Rb85 atoms. A simple pump-probe spectroscopy experiment is performed to generate non-degenerate blue light emission produced by the spontaneous decay route 5D3/2→6P3/2→5S1/2. By varying the relative intensity of the pump-probe combination, we can hover between regimes dominated by mechanisms such as double resonance optical pumping (DROP) and Autler-Townes splitting. The efficacy of the blue fluorescence (420nm) as a frequency offset reference is pronounced under the DROP regime due to its narrow (∼natural) linewidth. To provide further insight into the stability performance, the pump laser connecting the 5P3/2→5D3/2 transition is stabilized to the peak of the blue light with the help of a probe stabilized to the saturation absorption signal of the 5S1/2→5P3/2 transition. For this purpose, we used the coherence-induced modulation transfer technique. The error frequency noise power spectra and the subsequent Allan variance calculation clearly show that probe fluctuations are transferred to the pump laser because of an existing two-photon coherent coupling.

Determination of hyperfine structure constants of 5D5/2 and 7S1/2 states of rubidium in cascade atomic system

We present a method to precisely determine the hyperfine structure constants of the rubidium 5D5/2 and 7S1/2 states in a cascade atomic system. The probe laser is coupled to the 5S1/2→5P3/2 hyperfine transition, while the coupling laser is scanned over the 5P3/2→5D5/2(7S1/2) transition. The high-resolution double-resonance optical pumping spectra are obtained with two counter-propagating laser beams acting on rubidium vapor. The hyperfine splitting structures are accurately measured by an optical frequency ruler based on the acousto-optic modulator, thus, the magnetic dipole hyperfine coupling constant A and quadrupole coupling constant B are determined. It is of great significance for the atomic hyperfine structure and fundamental physics research.

Fluorescence double resonance optical pumping spectrum and its application for frequency stabilization in millimeter scale vapor cells

In recent years, we are observing substantial efforts towards the miniaturization of atomic cells to a millimeter scale and below, with the ultimate goal of enabling efficient and compact light vapor interactions. However, such miniaturization results in a reduction in optical path, effectively reducing the contrast of the optical signal. In order to overcome this obstacle, we have introduced and demonstrated a new approach of fluorescence double resonance optical pumping (FDROP) in the ladder-type atomic system. We have developed a theoretical model to predict the FDROP spectrum and validated this model using experimental results in a millimeter-size cell. We show that the contrast of fluorescence signal of the FDROP approach is higher than the transmission signal in the double resonance optical pumping approach. Taking advantage of this desired property, we have used the FDROP for the purpose of stabilizing the frequency of a laser operating at the telecom waveband with the hyperfine structure of the 5P3/2–4D5/2 transition in a millimeter-size cell. By beating the stabilized laser to another stabilized laser, we obtained frequency instability floor of 9 × 10−10 at around 1000 s in terms of Allan deviation. Such sources which are stabilized to miniaturized cells may play an important building block in diverse fields ranging e.g. from communication to metrology.

Atomic coherence effects in four-wave mixing process of a ladder-type atomic system.

We investigate the effects of atomic coherence on four-wave mixing (FWM), with respect to the transition routes between the hyperfine states in the 5S1/2-5P3/2-5D5/2 transition of 87Rb atoms. By comparing the FWM spectra with the electromagnetically induced transparency (EIT) spectra of the hyperfine states, we confirm that the FWM process is significantly influenced by both ladder-type and V-type two-photon coherences. From the observed FWM signal of each hyperfine structure, we clarify the role of two-photon coherence in the FWM process under EIT, double-resonance optical pumping (DROP), and two-photon absorption (TPA) conditions in a ladder-type atomic system, which is dependent on the open degree of the hyperfine states, the laser intensity, and the laser frequency detuning.

Measurement of absolute frequencies and hyperfine structure constants of4D5/2and4D3/2levels ofRb87andRb85using an optical frequency comb

We report the absolute frequency values of all (ten) hyperfine transitions of $5{P}_{3/2}\ensuremath{-}4{D}_{5/2}$ and $5{P}_{3/2}\ensuremath{-}4{D}_{3/2}$ for $^{87}\mathrm{Rb}$ and $^{85}\mathrm{Rb}$ atoms via the use of an optical frequency comb by measuring the frequency of a laser diode stabilized onto the line centers of the double-resonance optical pumping spectra. Here we report on the absolute frequencies for the two transitions $[{}^{85}\mathrm{Rb},\phantom{\rule{0.16em}{0ex}}5{P}_{3/2}({F}^{\ensuremath{'}}=4)\ensuremath{-}4{D}_{5/2}\phantom{\rule{0.16em}{0ex}}({F}^{\ensuremath{'}\ensuremath{'}}=3,4)]$. Furthermore, the frequency uncertainties are reduced significantly for the other transitions. Moreover, the magnetic dipole and the electric quadrupole hyperfine structure constants of $4{D}_{5/2}$ for $^{87}\mathrm{Rb}$ and $^{85}\mathrm{Rb}$ are determined by using the measured values of the absolute frequency.

Control of coherence in a ladder type system with double resonance optical pumping and electromagnetically induced transparency

It is shown that a repump laser (named repump after the convention used in the Laser Cooling experiment) can be effectively used to externally control the existing coherence in a ladder type atomic level coupling scheme comprising of 5S1/2(F = 2) → 5P3/2(F′) → 5D5/2(F′′) states of 87Rb atom. The repump laser connecting the F = 1 → F′ = 2 levels results in a substantial increment in the Electromagnetically Induced Transparency signal, with simultaneous reduction in Double Resonance Optical Pumping, throughout the entire Doppler width. Also, the optimization of EIT (both line width and strength) could be achieved by adjusting the intensity and the de-tuning of the repump laser, which successfully reduces incoherent pumping and related radiation trapping in the system. Of the two kinds of repump options, namely by connecting (i) the normal hyperfine levels and (ii) the degenerate Zeeman sublevels, the option (ii) has been found to be the more effective one for controlling the EIT in terms of ‘Gain’ and simultaneous preservation of narrow (often sub-natural) line width.

Determination of the hyperfine structure constants of theRb87andRb854D5/2state and the isotope hyperfine anomaly

The hyperfine structure (hfs) splittings of the $4{D}_{5/2}$ state for two isotopes of $^{87}\mathrm{Rb}$ and $^{85}\mathrm{Rb}$ atoms are measured based on double-resonance optical pumping spectra in a $5{S}_{1/2}\text{\ensuremath{-}}5{P}_{3/2}\text{\ensuremath{-}}4{D}_{5/2}$ ladder-type atomic system. The frequency calibration is performed by employing a wideband fiber-pigtailed phase-type electro-optic modulator together with a Fabry-P\'erot cavity to cancel the error arising from nonlinear frequency scanning. The hfs magnetic dipole constant $A$ of the $4{D}_{5/2}$ state is determined to be \ensuremath{-}16.801 \ifmmode\pm\else\textpm\fi{} 0.005 MHz for $^{87}\mathrm{Rb}$ and \ensuremath{-}4.978 \ifmmode\pm\else\textpm\fi{} 0.004 MHz for $^{85}\mathrm{Rb}$. The hfs electric quadrupole constant $B$ of the $4{D}_{5/2}$ state is determined to be 3.645 \ifmmode\pm\else\textpm\fi{} 0.030 MHz for $^{87}\mathrm{Rb}$ and 6.560 \ifmmode\pm\else\textpm\fi{} 0.052 MHz for $^{85}\mathrm{Rb}$. The values of $A$ and $B$ for the $^{87}\mathrm{Rb}4{D}_{5/2}$ state are twice as accurate as previous work with thermal atoms using a femtosecond laser comb and the values of $A$ and $B$ for the $^{85}\mathrm{Rb}4{D}_{5/2}$ state are 3 times and 25 times more accurate than previous work in laser-cooled atoms using Fabry--P\'erot interferometer, respectively. According to this high precision of the hfs constants and the previously measured nuclear $g$ factors of the two isotopes, the value of the $d$-electron hyperfine anomaly $^{87}\mathrm{\ensuremath{\Delta}}{}^{85}(4{D}_{5/2})$ is derived to be \ensuremath{-}0.0041 \ifmmode\pm\else\textpm\fi{} 0.0009.

Velocity Transfer Spectroscopy of Rb 420 nm Transition

We propose and demonstrate the velocity transfer spectroscopy of a V-type energy structure with Rb atoms at 420 nm transition. The weak oscillator strength of a lower excited state for V-type energy structure atoms limits the high signal-to-noise ratio of atomic laser spectroscopy, which can be usually realized by optical-optical double-resonance or double-resonance optical pumping for cascade-type energy structure atoms. For 87Rb atoms, the weak 420 nm transition spectrum between the energy level of 52 S1/2 and 62 P3/2 is transferred to the spectrum on lower excited states at 780 nm with strong oscillator strength, which is recorded by a 780 nm probe laser. This method, which is similar to the electron-shelving detection method, at a certain degree can indirectly measure a higher excited state transition with weak oscillator strength for any V-type energy structure of atoms by transferring the transition spectrum information of the very weak oscillator strength to the strong oscillator strength in an optical-optical double-resonance configuration.

Off-resonant double-resonance optical-pumping spectra and their application in a multiphoton cesium magneto-optical trap

We present an investigation of double-resonance optical pumping (DROP) spectra under the condition of single-photon frequency detuning based on a cesium 6S1/2–6P3/2–8S1/2 ladder-type system with a room-temperature vapor cell. Two DROP peaks are found, and their origins are explored. One peak has a narrow linewidth due to the atomic coherence for a counterpropagating configuration; the other peak has a broad linewidth, owing to the spontaneous decay for a copropagating configuration. This kind of off-resonant DROP spectrum can be used to control and offset-lock a laser frequency to a transition between excited states. We apply this technique to a multiphoton cesium magneto-optical trap, which can efficiently trap atoms on both red and blue sides of the two-photon resonance.

Application of repumping laser in optical switching

Abstract The application of electromagnetically induced transparency (EIT) in high speed optical switching has remained as a key topic in research related to all optical switching. Demonstration of optical switching through EIT realized under ladder (Ξ) level coupling has been reported earlier. Due to narrow linewidth ( Г EIT ) and low coherent dephasing rate ( γ ) the EIT needs to be prepared only once to demonstrate such switching action. However, in a Ξ system the EIT is accompanied with double resonance optical pumping (DROP) signal, which is limited by spontaneous decay ( Г ) rates. It has been shown by our group that the simultaneous presence of DROP–EIT combination paves the way for executing a kind of slow–fast switching action. However the focus always remain on improving the modulation depth in such type of coherence assisted switch. Here we report a possible way to improve modulation depth by using an additional (named ‘repumping’ after convention used in laser cooling experiments) laser in the Ξ system. The 5S 1/2 →5P 3/2 →5D 5/2 level coupling scheme of 87 Rb atom is used in the current experiment.

Study of the effect of repump laser on atomic line filter

The improvement in the performance of an atomic line filter (ALF) under the action of a repump laser is reported in the current experimental work. We address the issue of repumping by including an additional laser coupling the 5S1/2(F=1)→5P3/2(F′′=2,1,0) hyperfine levels whereas the optical filter action is exhibited through a pump–probe laser-induced excited state absorption {5S1/2(F=2)→5P3/2(F′=3)→5D3/2(F′′=3)} of the Rb87 atom. It is found that the application of the repump mechanism considerably influences the characterizing parameters (i.e., transmittance and width) of the ALF. To optimize the performance of the ALF, it is required to carefully choose the detuning and intensity of the repump laser for a fixed set of pump–probe combination. For this purpose, the effect of systematic change in detuning and intensity of the repump laser on the ALF signal is studied in detail. For example, it is experimentally found that ALF considerably benefits (∼30%) in transmittance from selective repumping of atoms. It is to be noted that, unlike earlier reports, where the frequency scale of the filter is calibrated with Faby–Perot etalons of comparatively larger free spectral range, the marking is done here with the help of double resonance optical pumping (DROP) signals. The DROP signals, which originate from two-photon coupling within the 5S→5P→5D hyperfine domain, also act as an indicator of the existing “Radiation Trapping” process in the cascade medium. The current study may help in improving the performance of narrow-bandwidth ALF, which is useful for free space optical communication systems and laser spectroscopy.

Erratum: Calculation of line shapes in double-resonance optical pumping [Phys. Rev. A80, 022509 (2009)

Erratum: Calculation of line shapes in double-resonance optical pumping [Phys. Rev. A<b>80</b>, 022509 (2009)