Cavity-enhanced spectroscopy of a few-ion ensemble in Eu3+:Y2O3
Bernardo Casabone, Julia Benedikter, Thomas Hümmer, Franziska Beck, Karmel de Oliveira Lima, Theodor W. Hänsch, Alban Ferrier, Philippe Goldner, Hugues de Riedmatten, David Hunger
We report on the coupling of the emission from a single europium-doped nanocrystal to a fiber-based microcavity under cryogenic conditions. As a first step, we study the sample properties and observe a strong correlation between emission lifetime and brightness, as well as a lifetime reduction for nanocrystals embedded in a polymer film. This is explained by differences in the local density of states. We furthermore quantify the scattering loss of a nanocrystal inside the cavity and use this to deduce the crystal size. Finally, by resonantly coupling the cavity to a selected transition, we perform cavity-enhanced spectroscopy to measure the inhomogeneous linewidth, and detect the fluorescence from an ensemble of few ions in the regime of power broadening. We observe an increased fluorescence rate consistent with Purcell enhancement. The results represent an important step towards the efficient readout of single rare-earth ions with excellent optical and spin coherence properties, which is promising for applications in quantum communication and distributed quantum computation.
We report the development of quantum microscopic theory of quasi-resonant dipole-dipole interaction in the ensembles of impurity atoms imbedded into transparent dielectric and located into Fabry-Perot cavity. On the basis of the general approach we study the simultaneous influence of the cavity and resonant dipole-dipole interaction on the shape of the line of atomic transition as well as on light trapping in dense impurity ensembles. We analyze this influence depending on the size of the ensemble, its density, as well as on r.m.s. deviation of the transition frequency shifts caused by the sym…
The efficiency of the frequency conversion process at the heart of Raman heterodyne spectroscopy was improved by nearly four orders of magnitude by resonant enhancement of both the pump and signal optical fields. Our results using an erbium doped Y$_2$SiO$_5$ crystal at temperatures near 4K suggest that such an approach is promising for the quantum conversion of microwave to optical photons.
We report a technique based upon the cavity ringdown method that enables to characterize the Brillouin gain coefficient directly in a laser cavity. Material gain, optical cavity parameters and lasing properties can be extracted from measurements whithin a single experiment.
Absorption spectroscopy is widely used to detect samples with spectral specificity. Here, we propose and demonstrate a method for enhancing the sensitivity of absorption spectroscopy. Exploiting multiple light scattering generated by a boron nitride (h-BN) scattering cavity, the optical path lengths of light inside a diffusive reflective cavity are significantly increased, resulting in more than ten times enhancement of sensitivity in absorption spectroscopy. We demonstrate highly sensitive spectral measurements of low concentrations of malachite green and crystal violet aqueous solutions. Bec…
In a previous letter we studied the giant optical nonlinearities of a Rydberg atomic medium within an optical cavity, in the Schwinger-Keldysh formalism. In particular, we calculated the non-linear contributions to the spectrum of the light transmitted through the cavity. In this article we spell out the essential details of this calculation, and we show how it can be extended to higher input photon numbers, and higher order correlation functions. As a relevant example, we calculate and discuss the three-photon correlation function of the transmitted light, and discuss its physical significanc…
Strong coupling of molecular vibrations to an infrared cavity mode affects their nature by creating dressed polariton states. We show how the single and double vibrational polariton manifolds may be controlled by varying the cavity coupling strength, and probed by a time domain 2DIR technique, Double Quantum Coherence (DQC). Applications are made to the amide-I ($CO$) and amide-II ($CN$) bond vibrations of $N-methylacetamide$ (NMA).
Efficient quantum memory is of paramount importance for long-distance quantum communications, as well as for complex large-scale computing architectures. We investigate the capability of Er$^{3+}$:Y$_2$SiO$_5$ crystal to serve as a quantum memory for the travelling microwave photons by employing techniques developed for dense optical ensembles. In our efforts to do so, we have performed high-resolution microwave spectroscopy of Er$^{3+}$:Y$_2$SiO$_5$, where we identified electronic spin as well as hyperfine transitions. Furthermore, we have explored spectral hole burning technique and studied …
Cavity ring-up spectroscopy (CRUS) provides an advanced technique to sense ultrafast phenomena, but there is no thorough discussion on its theory. Here we give a detailed theoretical analysis of CRUS with and without modal coupling, and present exact analytical expressions for the normalized transmission, which are very simple under certain reasonable conditions. Our results provide a solid theoretical basis for the applications of CRUS.
We demonstrate broadband and sensitive cavity ring-down spectroscopy using a near infrared frequency comb and a time-resolved Fourier transform spectrometer. The cavity decays are measured simultaneously and spectrally sorted, leading to purely exponential decays for each spectral element. The absorption spectra of atmospheric water and carbon dioxide are retrieved and demonstrate the high frequency resolution and absorption precision of the technique. The experimental apparatus, the measurement concept and the data treatment are described. The technique benefits from the advantages of cavity …
We describe methods using frequency combs and optical resonators for recording two-dimensional (2D) ultrafast spectroscopy signals with high sensitivity. By coupling multiple frequency combs to higher-order modes of one or more optical cavities, background-free, cavity-enhanced 2D spectroscopy signals are naturally generated via phase cycling. As in cavity-enhanced ultrafast transient absorption spectroscopy (CE-TAS), the signal to noise is enhanced by a factor proportional to the cavity finesse squared, so even using cavities of modest finesse, a very high sensitivity is expected, enabling ul…
We have recently introduced the Vernier-based Direct Frequency Comb Cavity-Enhanced Spectroscopy technique and we present the corresponding formalism for quantitative broadband spectroscopy. We achieve high sensitivity and broadband performance by acquiring spectra covering more than 2000 cm$^{-1}$ around 12600 cm$^{-1}$ (800 nm), resolving the 3$ν$+$δ$ band of water vapor and the entire A-band of oxygen in ambient air. 31 300 independent spectral elements are acquired at the second time scale with an absorption baseline noise of 2$\times$10$^{-8}$ cm$^{-1}$ providing a merit figure of 1,1.10$…
Rayleigh scattering is usually considered to be the elastic scattering of photons from sub-wavelength physical objects, such as small particles or molecules. Here, we present the spectroscopic study of the scattering properties of molecules embedded in an optical cavity under strong coupling conditions, where the collective interaction between the molecules and the cavity gives rise to composite light-matter excitations known as cavity polaritons. We show that the polaritonic states exhibit strong resonant Rayleigh scattering, reaching 25% efficiency. Since the polaritonic wavefunctions in suc…
We present a thorough analysis of the signal line shapes of Fourier transform-based noise-immune cavity-enhanced optical frequency comb spectroscopy (NICE-OFCS). We discuss the signal dependence on the ratio of the modulation frequency, f${_m}$, to the molecular line width, Γ. We compare a full model of the signals and a simplified absorption-like analytical model that has high accuracy for low f${_m}$/Γ ratios and is much faster to compute. We verify the theory experimentally by measuring and fitting NICE-OFCS spectra of CO${_2}$ at 1575 nm using a system based on an Er:fiber femtosecond lase…
We study the optical response of double optomechanical cavity system assisted by Rydberg atomic ensembles. And atomic ensembles are only coupled with one side cavity by a single cavity mode. It has been realized that a long-range manipulation for optical properties of hybrid system, by controlling the Rydberg atomic ensembles decoupled with the optomechanical cavity. Switching on the coupling between atoms and cavity mode, the original time reversal symmetry of double cavity structure has been broken. Based on the controlled optical non-reciprocity, we put forward the theoretical schemes of al…
本文报道了一种新的光腔衰荡光谱方法，样品气体处于饱和吸收区。这种技术允许去耦，并同时检索空腔背景和吸收信号，通过我们开发和测试的理论模型。利用光谱应用的高灵敏度和频率精度，首次测量了自然丰度的$^{17}$ O $^{12}$ C $^{16}$ O的激发振动态的超精细结构，其精度为$10^{-11}$中的几个部分。
We demonstrate incoherent broadband cavity enhanced absorption spectroscopy in the mid-infrared wave- length range from 3000 to 3450 nm using an all-fiber based supercontinuum source. Multi-components gas detection is performed and concentrations of acetylene and methane are retrieved with sub-ppm accuracy. A linear response to nominal gas concentrations is observed demonstrating the feasibility of the method for sensing applications.
Measurements of ultrahigh-fidelity absorption spectra can help validate quantum theory, engineer ultracold chemistry, and remotely sense atmospheres. Recent achievements in cavity-enhanced spectroscopy using either frequency-based dispersion or time-based absorption approaches have set new records for accuracy with uncertainties at the sub-per-mil level. However, laser scanning5 or susceptibility to nonlinearities limits their ultimate performance. Here we present cavity buildup dispersion spectroscopy (CBDS) in which the dispersive frequency shift of a cavity resonance is encoded in the cavit…
We report on the Doppler-free saturation spectroscopy of the nitrous oxide (N$_2$O) overtone transition at 1.28~$μ$m. This measurement is performed by the noise-immune cavity-enhanced optical heterodyne molecular spectroscopy (NICE-OHMS) technique based on the quantum-dot (QD) laser. A high intra-cavity power, up to 10~W, reaches the saturation limit of the overtone line using an optical cavity with a high finesse of 113,500. At a pressure of several mTorr, the saturation dip is observed with a full width at half-maximum of about 2~MHz and a signal-to-noise ratio of 71. To the best of our know…
We present a complex-valued electric field model for experimentally observed cavity transmission in coherent cavity-enhanced (CE) multiplexed spectroscopy (i.e., dual-comb spectroscopy, DCS). The transmission model for CE-DCS differs from that previously derived for Fourier-transform CE direct frequency comb spectroscopy [Foltynowicz et al., Appl. Phys. B 110, 163-175 (2013)] by the treatment of the local oscillator which, in the case of CE-DCS, does not interact with the enhancement cavity. Validation is performed by measurements of complex-valued near-infrared spectra of CO and CO$_2$ by an …
In whispering gallery mode resonator sensing applications, the conventional way to detect a change in the parameter to be measured is by observing the steady state transmission spectrum through the coupling waveguide. Alternatively, cavity ring-up spectroscopy (CRUS) sensing can be achieved transiently. In this work, we investigate CRUS using coupled mode equations and find analytical solutions with a large spectral broadening approximation of the input pulse. The relationships between the frequency detuning, coupling gap and ring-up peak height are determined and experimentally verified using…
Broadband ultrafast optical spectroscopy methods, such as transient absorption spectroscopy and 2D spectroscopy, are widely used to study molecular dynamics. However, these techniques are typically restricted to optically thick samples, such as solids and liquid solutions. In this article we discuss a cavity-enhanced ultrafast transient absorption spectrometer covering almost the entire visible range with a detection limit of $Δ$OD $ < 1 \times 10^{-9}$, extending broadband all-optical ultrafast spectroscopy techniques to dilute beams of gas-phase molecules and clusters. We describe the techni…
The achievable instrument sensitivity is a critical parameter for the continued development of THz applications. Techniques such as Cavity-Enhanced Techniques and Cavity Ring Down Spectroscopy have not yet been employed at THz frequency due to the difficulties to construct a high finesse Fabry-Pérot cavity. Here, we describe such a THz resonator based on a low-loss oversized corrugated waveguide with highly reflective photonic mirrors obtaining a finesse above 3000 around 620 GHz. These components enable a Fabry-Perot THz Absorption Spectrometer with an equivalent interaction length of one kil…
Vertical external-cavity surface-emitting lasers (VECSELs) augmented by intra-cavity nonlinear optical frequency conversion have emerged as an attractive light source of ultraviolet to visible light for demanding scientific applications, relative to other laser technologies. They offer high power, low phase noise, wide frequency tunability, and excellent beam quality in a simple and inexpensive system architecture. Here, we characterize the frequency stability of an intra-cavity frequency-doubled VECSEL with 690 mW of output power at 475 nm using the delayed self-heterodyne technique and direc…
Mode-resolved dual-comb spectroscopy (DCS) is an emerging spectroscopic tool with the potential to simultaneously achieve a broad spectral coverage and ultrahigh spectral resolution in terahertz (THz) spectroscopy. However, the need for two independently stabilized ultrafast lasers significantly hampers the potential application of DCS techniques. In this article, we demonstrate mode-resolved DCS in the THz region based on a free-running single-cavity dual-comb fiber laser with adaptive sampling. Low-pressure spectroscopy of acetonitrile gas with absorption features approaching the Doppler lim…
Advances in high-resolution laser spectroscopy have enabled many scientific breakthroughs in physics, chemistry, biology and astronomy. Optical frequency combs have pushed measurement limits with ultrahigh-frequency accuracy and fast-measurement speed while tunable diode laser spectroscopy is used in scenarios that require high power and continuous spectral coverage. Despite these advantages of tunable diode laser spectroscopy, it is challenging to precisely determine the instantaneous frequency of the laser because of fluctuations in the scan speed. Here we demonstrate a simple spectroscopy s…
We report the first experimental demonstration of frequency-locking of an extended-cavity quantum-cascade-laser (EC-QCL) to a near-infrared frequency comb. The locking scheme is applied to carry out absolute spectroscopy of N2O lines near 7.87 μm with an accuracy of ~60 kHz. Thanks to a single mode operation over more than 100 cm^{-1}, the comb-locked EC-QCL shows great potential for the accurate retrieval of line center frequencies in a spectral region that is currently outside the reach of broadly tunable cw sources, either based on difference frequency generation or optical parametric oscil…
We report the most accurate measurement of the position of the weak quadrupole S(2) 2-0 line in D$_2$. The spectra were collected with a frequency-stabilized cavity ring-down spectrometer (FS-CRDS) with an ultra-high finesse optical cavity ($\mathcal{F}$ = 637 000) and operating in the frequency-agile, rapid scanning spectroscopy (FARS) mode. Despite working in the Doppler-limited regime, we reached 40 kHz of statistical uncertainty and 161 kHz of absolute accuracy, achieving the highest accuracy for homonuclear isotopologues of molecular hydrogen. The accuracy of our measurement corresponds t…
We report Doppler-free two-photon absorption of N$_2$O at $λ$ = 4.53 $μ$m, measured by cavity ring-down spectroscopy. High power was achieved by optical self-locking of a quantum cascade laser to a linear resonator of finesse $F$ = 22730, and accurate laser detuning over a 400 MHz range was measured relative to an optical frequency comb. At a sample pressure of p = 0.13 kPa, we report a large two-photon cross-section of $σ_{13}^{(2)}$ = 8.0 $\times$ 10$^{-41}$ cm$^4$ s molecule$^{-1}$ for the $Q$(18) rovibrational transition at a resonant frequency of $ν_0$ = 66179400.8 MHz.
One way of optically monitoring molecule concentrations is to utilise the high sensitivity of the transmission and reflection rates of Fabry-Perot cavities to changes of their optical properties. Up to now, intrinsic and extrinsic Fabry-Perot cavity sensors have been considered with analytes either being placed inside the resonator or coupled to evanescent fields on the outside. Here we show that Fabry-Perot cavities can also be used to monitor molecule concentrations non-invasively and remotely, since the reflection of light from the target molecules back into the Fabry-Perot cavity adds upwa…
