We present two-color modulation transfer spectroscopy as a tool for precision studies of atomic properties of excited states. The bi-colored technique addresses a narrow set of velocity groups of a thermal atomic vapour using a two-step transition to "burn a hole" in the velocity distribution. The resulting spectrum presents sub-Doppler linewidths, good signal to noise ratio and the trademark sidebands that work as an in situ ruler for the energy spacing between atomic resonances. The spectra obtained can be used for different applications such as measurements of energy splittings or stabilization of laser frequencies to excited atomic transitions.
We present a technique for simultaneous laser frequency stabilization on transitions of multiple atomic species with a single optical setup. The method is based on modulation transfer spectroscopy and the signals are separated by modulating at different frequencies and electronically filtered. As a proof of concept, we demonstrate simultaneous spectroscopy of the potassium D$_1$, D$_2$ and rubidium D$_2$ transitions. The technique can easily be extended to other atomic species and allows the development of versatile and compact frequency reference modules.
With the uncertainty of the optical clocks improving to the order of 10-18, the probe light used to detect the clock transition has demonstrated nonnegligible Stark shift, provoking to precisely evaluate this shift. Here, we demonstrate a frequency modulation technique to realize a large measurement lever arm of the probe Stark shift with no cost of the measurement accuracy of the interleaved stabilization method. This frequency-modulated spectrum is theoretical described and experimental verified. The probe Stark shift coefficient of the 87Sr optical lattice clock is experimentally determined…
Band-resolved frequency modulation spectroscopy is a common method to measure weak signals of radiative ensembles. When the optical depth of the medium is large, the signal drops exponentially and the technique becomes ineffective. In this situation, we show that a signal can be recovered when a larger modulation index is applied. Noticeably, this signal can be dominated by the natural linewidth of the resonance, regardless of the presence of inhomogeneous line broadening. We implement this technique on a cesium vapor, and then explore its main spectroscopic features. This work opens the road …
Isotope selective optical excitation of atoms is important for experiments with neutral atoms, metrology, and work with trapped ions, including quantum information processing. Polarization-enhanced absorption spectroscopy is used to frequency stabilise a tunable external cavity laser diode system at 398.9 nm for isotope selective photoionization of neutral Yb atoms. This spectroscopy technique is used to measure isotope resolved dispersive features from transitions within a see through configuration Ytterbium hollow-cathode discharge lamp. This Doppler-free dichroic polarization spectroscopy i…
We present a general analysis for determining the optimal modulation parameters for the modulation transfer spectroscopy scheme. The results are universally valid and can be applied to spectroscopy of any atomic species requiring only the knowledge of the effective linewidth $Γ_{eff}$. A signal with optimized slope and amplitude is predicted for a large modulation index $M$ and a modulation frequency comparable to the natural linewidth of the spectroscopic transition. As a result of competing practical considerations, a modulation index in the range of $3 \le M \le 10$ has been identified as o…
We experimentally and theoretically show that the electron energy spectra strongly depend on the relative helicity in highly intense, circularly polarized two-color laser fields which is an unexpected finding. The employed counter-rotating two-color (CRTC) fields and the co-rotating two-color (CoRTC) fields are both a superposition of circularly polarized laser pulses at a central wavelength of 390 nm and 780 nm (intensitiy ratio $I_{390}/I_{780}\approx 250$). For the CRTC field, the measured electron energy spectrum is dominated by peaks that are spaced by 3.18 eV (corresponds to the photon e…
Analysis of the frequency shift in coherent population trapping resonance's dynamic continuous-wave spectroscopy at the phase-jump modulation and its comparison with the conventional approach
P. N. Lebedev Physical Institute of the Russian Academy of Sciences（俄罗斯科学院列别杰夫物理研究所）
A method of dynamic continuous-wave spectroscopy of coherent population trapping (CPT) resonances using phase modulation of the jump type is developed. The time evolution of the spectroscopic signal is investigated. A method for the formation of an error signal for frequency stabilization is proposed. We show that our approach has a reduced sensitivity to the lineshape asymmetry of the CPT resonance. The experimental results are in good qualitative agreement with theoretical predictions based on a mathematical model of a three-level $Λ$ system in a bichromatic field. This method can be used in…
We develop and study quantum and semi-classical models of Rydberg-atom spectroscopy in amplitude-modulated optical lattices. Both initial- and target-state Rydberg atoms are trapped in the lattice. Unlike in any other spectroscopic scheme, the modulation-induced ponderomotive coupling between the Rydberg states is spatially periodic and perfectly phase-locked to the lattice trapping potentials. This leads to a novel type of sub-Doppler mechanism, which we explain in detail. In our exact quantum model, we solve the time-dependent Schrödinger equation in the product space of center-of-mass (COM)…
Ultrastable frequency reference at 1.56 μm using a CO molecular overtone transition with the noise immune cavity-enhanced optical heterodyne molecular spectroscopy method
报道了一种基于一氧化碳12 C 16 O在1563 nm处的3ν振转结合带的超稳分子钟。激光稳定方案是基于频率调制（FM）饱和光谱在高精细度超低膨胀（ULE）玻璃光学腔中使用CO作为长期稳定腔谐振的分子参考。采用NICEOHMS FM调制方法，以保持高的信噪比，并避免由高精细度腔将激光频率噪声转换为幅度噪声。我们报告1秒时的艾伦偏差为1.8x10-12，在1000秒的平均后提高到3.5x10-14。
Locking of a laser frequency to an atomic or molecular resonance line is a key technique in applications of laser spectroscopy and atomic metrology. Modulation transfer spectroscopy (MTS) provides an accurate and stable laser locking method which has been widely used. Normally, the frequency of the MTS signal would drift due to Zeeman shift of the atomic levels and rigorous shielding of stray magnetic field around the vapor cell is required for the accuracy and stability of laser locking. Here on the contrary, by applying a transverse bias magnetic field, we report for the first time observati…
We have found that the error-signal frequency corresponding to the coherent population trapping resonance can be displaced from that of "$0-0$" transition unperturbed by the optical field, although the frequency is not sensitive to changes in its intensity. We consider the double $Λ$-system of levels interacting with the asymmetric polychromatic optical field to demonstrate that this effect arises due to intensity nonlinearity of the error-signal frequency shift. The experiment with $^{87}$Rb atoms in Ar-N$_2$ buffer gas atomic cell shows how the displacement value depends on different paramet…
Active frequency stabilization of a laser to an atomic or molecular resonance underpins many modern-day AMO physics experiments. With a flat background and high signal-to-noise ratio, modulation transfer spectroscopy (MTS) offers an accurate and stable method for laser locking. Despite its benefits, however, the four-wave mixing process that is inherent to the MTS technique entails that the strongest modulation transfer signals are only observed for closed transitions, excluding MTS from numerous applications. Here, we report for the first time the observation of a magnetically tunable MTS err…
Phase-of-the-phase spectroscopy using two-color colinearly polarized laser pulses has been introduced and experimentally applied to strong-field tunneling ionization in S. Skruszewicz et al., Phys. Rev. Lett. 115, 043001 (2015) and recently to multiphoton ionization in M. A. Almajid et al., J. Phys. B: At. Mol. Opt. Phys. 50, 194001 (2017). The idea behind phase-of-the-phase spectroscopy is to study in a systematic way the change in the photoelectron yield as a function of the relative phase between the strong fundamental field component (of carrier frequency $ω$) and a weak, second color comp…
Production of electron-positron pairs from vacuum in strong bichromatic electric fields, oscillating in time with a fundamental frequency and its second harmonic, is studied. Strong-field processes occuring in such field configurations are generally known to be sensitive to the relative phase between the field modes. Phase-of-the-phase spectroscopy has recently been introduced in the context of strong-field photoionization as a systematic means to analyze these coherence effects. We apply this method to field-induced pair production by calculating the phase dependence of the momentum-resolved …
Compactness, robustness and autonomy of optical frequency references are prerequisites for reliable operation in mobile systems, on ground as well as in space. We present a standalone plug and play optical frequency reference device based on frequency modulation spectroscopy of the D2-transition in rubidium at 780 nm. After a single button press the hand-sized laser module, based on the micro-integrated laser-optical bench described in [J. Opt. Soc. Am. B 38, 1885-1891 (2021)], works fully autonomous and generates 6 mW of frequency stabilized light with a relative frequency instability of 1.4e…
Phase-of-the-phase (PoP) spectroscopy is extended to two-color laser fields having a circularly counter-rotating polarization. In particular, the higher harmonics of the (two-color) phase information are analyzed in order to extract the laser-coherent part of the photoelectron spectra taken under complex target conditions. We illustrate this with a proof-of-principle simulation by considering strong-field electron emission from argon atoms within helium nanodroplets under realistic experimental conditions, i.e., a limited number of photoemission events. Multiple elastic scattering on neutral h…
Color centered-based single photon emitters in hexagonal boron nitride (h-BN) have shown promising photophysical properties as sources for quantum light emission. Despite significant advances towards such a goal, achieving lifetime-limited quantum light emission in h-BN has proven to be challenging, primarily due to various broadening mechanisms including spectral diffusion. Here, we propose and experimentally demonstrate suppression of spectral diffusion by applying an electrostatic field. We observe both Stark shift tuning of the resonant emission wavelength, and emission linewidth reduction…
