We have performed high resolution spectroscopy of rubidium with a single mode continuous wave distributed feedback (DFB) laser diode. The saturation spectrum of the D_2-line of 85Rb and 87Rb was recorded with a resolution close to the natural line width. The emission frequency was actively stabilized to Doppler-free transitions with a relative accuracy of better than 7 parts in 10^9 using commercially available servo devices only. An output power of 80 mW was sufficient to allow for two-photon spectroscopy of the 5S-5D-transition of 87Rb. Further, we report on the spectral properties of the DFB diode, its tuning range and its frequency modulation properties. The line width of the diode laser, determined with high resolution Doppler free two photon spectroscopy, was 4 MHz without applying any active stabilization techniques. For time scales below 5 us the line width drops below 2 MHz.
The photoionisation of rubidium in strong infra-red laser fields based on ab initio calculations was investigated. The bound and the continuum states are described with Slater orbitals and Coulomb wave packets, respectively. The bound state spectra were calculated with the variational method and we found it reproduced the experimental data within a few percent accuracy. Using the similar approach, ionisation of Rb was also successfully investigated. The effects of the shape and the parameters of the pulse to the photoionisation probabilities and the energy spectrum of the ionised electron are …
Employing recent developed magneto-optical trap recoil ion momentum spectroscopy (MOTRIMS) combining cold atom, strong laser pulse, and ultrafast technologies, we study momentum distributions of the multiply ionized cold rubidium (Rb) induced by the elliptically polarized laser pulses (35 fs, $1.3 \times 10^{15}$ W/cm$^2$). The complete vector momenta of Rbn+ ions up to charge state n = 4 are recorded with extremely high resolution (0.12 a.u. for Rb$^+$). Variations of characteristic multi-bands displayed in momentum distributions, as the ellipticity varies from the linear to circular polariza…
AWAKE develops a new plasma wakefield accelerator using the CERN SPS proton bunch as a driver. The proton bunch propagates through a 10 m long rubidium plasma, induced by an ionizing laser pulse. The co-propagation of the laser pulse with the proton bunch seeds the self modulation instability of the proton bunch that transforms the bunch to a train with hundreds of bunchlets which drive the wakefields. Therefore the plasma radius must exceed the proton bunch radius. Schlieren imaging is proposed to determine the plasma radius on both ends of the vapor source. We use Schlieren imaging to estima…
It is known from ensemble measurements that rubidium atoms trapped in solid parahydrogen have favorable properties for quantum sensing of magnetic fields. To use a single rubidium atom as a quantum sensor requires a technique capable of efficiently measuring the internal state of a single atom, such as laser-induced fluorescence. In this work we search for laser-induced fluorescence from ensembles of rubidium atoms trapped in solid parahydrogen and, separately, in solid neon. In parahydrogen we find no evidence of fluorescence over the range explored, and place upper limits on the radiative br…
Data students collect from the typical advanced undergraduate laboratory on Saturated Absorption Spectroscopy (SAS) of rubidium can be used to measure the isotope shift and thus leads to an estimate of the isotopic ground state energy shift. This helps students refine their `picture' of the atomic ground state. We describe theoretically why this laboratory works well with free-running laser diodes, demonstrate it experimentally using these lasers tuned to either principal near-infrared transitions, and show an extension of the laboratory using the modulation transfer spectroscopy method.
We present the first extended-cavity diode laser in Littrow configuration operating in the cyan wavelength range around 497 nm. The gallium-nitride based diode laser features a free-space output with up to 60 mW, operates in a single frequency mode, is tunable over a range of more than 8 nm and has a Lorentzian linewidth of less than 90 kHz. A detailed characterization of the tuning capabilities of the diode laser and its emission spectrum is provided. This compact, simple and low cost laser source replaces more complex systems based on frequency doubling and therefore simplifies the developme…
We have developed a versatile pulsed laser system for high precision magnetometry. The operating wavelength of the system can be configured to optically pump alkali vapors such as rubidium and cesium. The laser system consists of an auto-locked, interference filter stabilized, external cavity diode laser (ECDL), a tapered waveguide amplifier, and a pulsing module. The auto-locking controller can be used by an untrained operator to stabilize the laser frequency with respect to a library of atomic, molecular, and solid-state spectral markers. The ECDL output can be amplified from 20 mW to 2 W in…
The knowledge of the frequency noise spectrum of a diode laser is of interest in several high resolution experiments. Specifically, in laser-pumped vapor cell clocks, it is well established that the laser frequency noise plays a role in affecting the clock performances. It is then important to characterize the frequency noise of a diode laser, especially since such measurements are rarely found in the literature and hardly ever provided by vendors. In this paper, we describe a technique based on a frequency-to-voltage converter that transforms the laser frequency fluctuations into voltage fluc…
We present an experimental scheme that produces Doppler-free spectra of the $5s \to 6p $ second resonance transition in atomic rubidium. The experiment uses the saturation of the cascade fluorescence that occurs when thermal rubidium atoms interact with two counterpropagating $420 $ nm laser beams of comparable intensity. Part of the excited atomic population goes through the $5p_{3/2}$ level which then decays by emission of $780$ nm photons. Narrow dips appear in this otherwise broad $780$ nm fluorescence, which allows resolution of the $6p_{3/2}$ hyperfine structure. A rate equation model is…
We experimentally demonstrate a one-color two-photon transition from the $5\mathit{S}_{1/2}$ ground state to the $6\mathit{S}_{1/2}$ excited state in rubidium (Rb) vapor using a continuous wave laser at 993 nm. The Rb vapor contains both isotopes ($^{85}$Rb and $^{87}$Rb) in their natural abundances. The electric dipole allowed transitions are characterized by varying the power and polarization of the excitation laser. Since the optical setup is relatively simple, and the energies of the allowed levels are impervious to stray magnetic fields, this is an attractive choice for a frequency refere…
Atomic frequency reference at 1033 nm for ytterbium (Yb)-doped fiber lasers and applications exploiting a rubidium (Rb) 5$S_{1/2}$ to 4$D_{5/2}$ one-colour two-photon transition
We report on the generation of 500 mW of spectrally pure laser light at the 460.86 nm transition used for laser cooling of strontium atoms. To this end we inject a high power single mode laser diode with light from a stabilized extended cavity diode laser. To optimize and monitor the injection status and the spectral purity of the slave diode we developed a novel technique that uses a single passive optical element. A narrow band interference filter generates a suitable monitoring signal without any additional electronics for post processing of the data. Our method greatly simplifies the daily…
We report a simple tunable master-slave laser injection-lock scheme for atomic physics experiments. Seed light from an external cavity diode laser is injected into a high-power fiber-pigtailed diode laser via a fiber optic circulator. High-power outputs (up to $\sim$600 mW) at the injected frequency have been obtained in a single-mode fiber with tuning over a wide wavelength range ($\sim$15 nm). The scheme is simpler and more cost-effective than the traditional scheme of free-space injection-locking.
We present an inexpensive, low-noise ($<260~μ$V$_{rms}$, 0.1~Hz - 100~kHz) design for a piezo driver suitable for frequency tuning of external-cavity diode lasers. This simple driver improves upon many commercially available drivers by incorporating circuitry to produce a `feed-forward' signal appropriate for making simultaneous adjustments to the piezo voltage and laser current, enabling dramatic improvements in mode-hop-free laser frequency tuning range. We present the theory behind our driver's operation, characterize its output noise, and demonstrate its use in absorption spectroscopy on t…
Laser intensity noise suppression has essential effects on preparation and characterization of the audio-frequency squeezed vacuum state of light based on a sub-threshold optical parametric oscillator (OPO).We have implemented two feedback loops by using relevant acousto-optical modulators (AOM) to stabilize the intensity of 795-nm near infrared (NIR) fundamental laser and 397.5-nm ultraviolet (UV) laser generated by cavity-enhanced frequency doubling.Typical peak-to-peak laser intensity fluctuation with a bandwidth of $\sim10$ kHz in a half hour has been improved from $\pm7.45$$\%$ to $\pm0.0…
We propose and demonstrate pump-probe spectroscopy of rubidium absorption which reveals the sub-Doppler hyperfine structure of the $^{5}$S$_{1/2} \leftrightarrow$ $^{5}$P$_{3/2}$ (D2) transitions. The counter propagating pump and probe lasers are independently tunable in frequency, with the probe operating at the single-photon-level. The two-dimensional spectrum measured as the laser frequencies are scanned shows fluorescence, Doppler-broadened absorption dips and sub-Doppler features. The detuning between the pump and probe lasers allows compensation of the Doppler shift for all atomic veloci…
We report on an interference-filter-stabilized external cavity diode laser using a gallium-nitride-based violet laser diode. Surface-activated-bonded glass substrates were employed as cat's eye output couplers in order to suppress power degradation due to optical damage. From the results of a long-term frequency-stabilization test, mode-hop-free operation for about one week was demonstrated. After a continuous operation of about three weeks, the power degradation was less than 10$\%$. The results show the potential of such interference-filter-stabilized external cavity diode lasers for practic…
The exquisite properties of Rydberg levels make them particularly appealing for emerging quantum technologies. The lifetime of low-angular-momentum laser-accessible levels is however limited to a few $100\,μ\mathrm{s}$ by optical transitions and microwave blackbody radiation (BBR) induced transfers at room temperature. A considerable improvement would be obtained with the few $10\,\mathrm{ms}$ lifetime of circular Rydberg levels in a cryogenic environment reducing the BBR temperature. We demonstrate the preparation of long-lived circular Rydberg levels of laser-cooled Rubidium atoms in a cryos…
