Cavity Output Research Articles

Measurement of CO2 by Wavelength Modulated Reinjection Off-Axis Integrated Cavity Output Spectroscopy at 2 μm

A high sensitivity wavelength modulated reinjection off-axis integrated cavity output spectroscopy (WM-RE-OA-ICOS) experimental setup was built at a 2 μm band. On the basis of an off-axis integrated output spectroscopy (OA-ICOS), combined with an optical reinjection (RE) approach to improve signal intensity, and wavelength modulation spectroscopy (WMS) to improve the signal-to-noise ratio (SNR) of the system, the experimental study of trace CO2 with high sensitivity was carried out using the setup. The performance was compared and evaluated, and the results show that: Compared with the OA-ICOS, the wavelength modulated reinjection OA-ICOS enhanced the signal intensity by 6.3 times, and the SNR increased 7.2 times from 179 to 1288. The Allan variance results showed that the detection limit of the system is 0.35 ppm when the average system time is 230 s. The setup was used to measure the indoor CO2 concentration for a long time (22 h), and the measured results were in line with the actual concentration change. The proposed method shows good performance enhancement for the OA-ICOS system in trace gas measurements.

Wide dynamic detection range of methane gas based on enhanced cavity absorption spectroscopy

Integrated cavity output spectroscopy (ICOS) is an effective technique in trace gase detection. The strong absorption due to the long optical path of this method makes it challenging in the application scenes that have large gas concentration fluctuation, especially when the gas concentration is high. In this paper, we demonstrate an extension of the dynamic range of ICOS by using a detuned laser combined with an off-axis integrating cavity. With this, we improve the upper limit of the dynamic detection range from 0.1% (1000 ppm) to 20% of the gas concentration. This method provides a way of using ICOS in the applications with unpredictable gas concentrations such as gas leak detection, ocean acidification, carbon sequestration, etc.

Subradiant-to-Subradiant Phase Transition in the Bad Cavity Laser.

We show that the onset of steady-state superradiance in a bad cavity laser is preceded by a dissipative phase transition between two distinct phases of steady-state subradiance. The transition is marked by a nonanalytic behavior of the cavity output power and the mean atomic inversion, as well as a discontinuity in the variance of the collective atomic inversion. In particular, for repump rates below a critical value, the cavity output power is strongly suppressed and does not increase with the atom number, while it scales linearly with atom number above this value. Remarkably, we find that the atoms are in a macroscopically entangled steady state near the critical region with a vanishing fraction of unentangled atoms in the large atom number limit.

Airborne Mid-Infrared Cavity enhanced Absorption spectrometer (AMICA)

Abstract. We describe the Airborne Mid-Infrared Cavity enhanced Absorption spectrometer (AMICA) designed to measure trace gases in situ on research aircraft using Off-Axis Integrated Cavity Output Spectroscopy (OA-ICOS). AMICA contains two largely independent and exchangeable OA-ICOS arrangements, allowing for the simultaneous measurement of multiple substances in different infrared wavelength windows tailored to scientific questions related to a particular flight mission. Three OA-ICOS setups have been implemented with the aim to measure OCS, CO2, CO, and H2O at 2050 cm−1; O3, NH3, and CO2 at 1034 cm−1; and HCN, C2H2, and N2O at 3331 cm−1. The 2050 cm−1 setup has been characterized in the laboratory and successfully used for atmospheric measurements during two campaigns with the research aircraft M55 Geophysica and one with the German HALO (High Altitude and Long Range Research Aircraft). For OCS and CO, data for scientific use have been produced with 5 % accuracy (15 % for CO below 60 ppb, due to additional uncertainties introduced by dilution of the standard) at typical atmospheric mixing ratios and laboratory-measured 1σ precision of 30 ppt for OCS and 3 ppb for CO at 0.5 Hz time resolution. For CO2, high absorption at atmospheric mixing ratios leads to saturation effects that limit sensitivity and complicate the spectral analysis, resulting in too large uncertainties for scientific use. For H2O, absorption is too weak to be measured at mixing ratios below 100 ppm. By further reducing electrical noise and improving the treatment of the baseline in the spectral retrieval, we hope to improve precision for OCS and CO, resolve the issues inhibiting useful CO2 measurements, and lower the detection limit for H2O. The 1035 and 3331 cm−1 arrangements have only partially been characterized and are still in development. Although both setups have been flown and recorded infrared spectra during field campaigns, no data for scientific use have yet been produced due to unresolved deviations of the retrieved mixing ratios to known standards (O3) or insufficient sensitivity (NH3, HCN, C2H2, N2O). The ∼100 kg instrument with a typical in-flight power consumption of about 500 VA is dimensioned to fit into one 19 in. rack typically used for deployment inside the aircraft cabin. Its rugged design and a pressurized and temperature-stabilized compartment containing the sensitive optical and electronic hardware also allow for deployment in payload bays outside the pressurized cabin even at high altitudes of 20 km. A sample flow system with two parallel proportional solenoid valves of different size orifices allows for precise regulation of cavity pressure over the wide range of inlet port pressures encountered between the ground and maximum flight altitudes. Sample flow of the order of 1 SLM (standard litre per minute) maintained by an exhaust-side pump limits the useful time resolution to about 2.5 s (corresponding to the average cavity flush time), equivalent to 500 m distance at a typical aircraft speed of 200 m s−1.

Energy-level attraction and heating-resistant cooling of mechanical resonators with exceptional points

We study the energy-level evolution and ground-state cooling of mechanical resonators under a synthetic phononic gauge field. The tunable gauge phase is mediated by the phase difference between the $\mathcal{PT}$- and anti-$\mathcal{PT}$-symmetric mechanical couplings in a multimode optomechanical system. The transmission spectrum then exhibits the asymmetric Fano line shape or double optomechanically induced transparency by modulating the gauge phase. Moreover, the eigenvalues will collapse and become degenerate although the mechanical coupling is continuously increased. Such counterintuitive energy-attraction, instead of anti-crossing, attributes to destructive interferences between $\mathcal{PT}$- and anti-$\mathcal{PT}$-symmetric couplings. We find that the energy-attraction, as well as the accompanied exceptional points (EPs), can be more intuitively observed in the cavity output power spectrum where the mechanical eigenvalues correspond to the peaks. For mechanical cooling, the average phonon occupation number becomes minimum at these EPs. Especially, phonon transport becomes nonreciprocal and even ideally unidirectional at the EPs. Finally, we propose a heating-resistant ground-state cooling based on the nonreciprocal phonon transport, which is mediated by the gauge field. Towards the quantum regime of macroscopic mechanical resonators, most optomechanical systems are ultimately limited by their intrinsic cavity or mechanical heating. Our work revealed that the thermal energy transfer can be blocked by tuning the gauge phase, which supports a promising route to overpass the notorious heating limitations.

Investigation of a polarization-based Cr:forsterite laser resonator cavity

A polarization-based laser resonator cavity with continuous variable output coupling is investigated using Cr:forsterite crystal as the gain medium. The confocal resonator cavity houses intracavity polarization optics for continuous tuning of the output coupler. The variation in the coupling efficiency is suitably explained by calculation based on Jones matrix formalism. The established resonator cavity is found to be advantageous for fine control over the cavity output energy, intracavity energy, cavity buildup time, laser pulse width, and threshold pump energy. The theoretically estimated output energy is in good agreement with the experimental results. The investigated system provides flexible optimization of the laser parameters and can be useful for all optical synchronization of multiple laser pulses as desired in many spectroscopic experiments.

Optomechanical cooling with coherent and squeezed light: The thermodynamic cost of opening the heat valve

Ground-state cooling of mechanical motion by coupling to a driven optical cavity has been demonstrated in various optomechanical systems. In our work, we provide a so far missing thermodynamic performance analysis of optomechanical sideband cooling in terms of a heat valve. As performance quantifiers, we examine not only the lowest reachable effective temperature (phonon number) but also the evacuated-heat flow as an equivalent to the cooling power of a standard refrigerator, as well as appropriate thermodynamic efficiencies, which all can be experimentally inferred from measurements of the cavity output light field. Importantly, in addition to the standard optomechanical setup fed by coherent light, we investigate two recent alternative setups for achieving ground-state cooling: replacing the coherent laser drive by squeezed light or using a cavity with a frequency-dependent (Fano) mirror. We study the dynamics of these setups within and beyond the weak-coupling limit and give concrete examples based on parameters of existing experimental systems. By applying our thermodynamic framework, we gain detailed insights into these three different optomechanical cooling setups, allowing a comprehensive understanding of the thermodynamic mechanisms at play.

Low-Threshold Microlasers Based on Holographic Dual-Gratings.

Among the efforts to improve the performances of microlasers, optimization of the gain properties and cavity parameters of these lasers has attracted significant attention recently. Distributed feedback lasers, as one of the most promising candidate technologies for electrically pumped microlasers, can be combined with dual-gratings. This combination provides additional freedom for the design of the laser cavity. Here, a holographic dual-grating is designed to improve the distributed feedback laser performance. The holographic dual-grating laser consists of a colloidal quantum dot film with two parallel gratings, comprising first-order (210 nm) and second-order (420 nm) gratings that can be fabricated easily using a combination of spin coating and interference lithography. The feedback and the output from the cavity are controlled using the first-order grating and the second-order grating, respectively. Through careful design and analysis of the dual-grating, a balance is achieved between the feedback and the cavity output such that the lasing threshold based on the dual-grating is nearly half the threshold of conventional distributed feedback lasers. Additionally, the holographic dual-grating laser shows a high level of stability because of the high stability of the colloidal quantum dots against photobleaching.

Spectroscopic investigation of hydrogen and triple-oxygen isotopes in atmospheric water vapor and precipitation during Indian monsoon season

ABSTRACT Water vapor, the most important greenhouse gas in the atmosphere, has four natural stable isotopologues (H2 16O, H2 17O, H2 18O and HD16O), and their isotopic compositions can be used as hydrological tracers. But the underlying processes and pattern-dynamics of the isotopic compositions of atmospheric water vapor and precipitation in response to various meteorological conditions during monsoon season in a tropical hot and humid region is poorly understood. Here, we present results of H and triple-O-isotopes of water in precipitation and atmospheric water vapor during monsoon season exploiting high-resolution integrated cavity output spectroscopy technique. We observed a distinct temporal variation of the isotopic compositions of water at different phases of the monsoon. The diurnal patterns of the isotopic variations were influenced by the local meteorological factors such as temperature, relative humidity and amount of precipitation. We also investigated the monsoonal dynamics of the second-order isotopic parameters, so-called d-excess and 17O-excess along with the influence of local meteorological factors on isotopic variations to improve our understanding of the underlying isotopic fractionation processes. Consequently, our results provide a unique isotopic-fingerprint dataset of rainwater and atmospheric water vapor for a tropical region and thus shed a new light on hydrological and meteorological processes in the atmosphere.

Unconventional Photon Blockade in Quantum‐Well Microcavities with Squeezed Light

The single‐photon blockade effect arising in a cavity containing a quantum well and interacting with squeezed light, resulting from a down‐conversion process through a nonlinear medium, is investigated. Optical parametric oscillator (OPO) materials with positive and negative second‐order susceptibilities are considered. By solving the master equation analytically in the weak‐driving limit and calculating the second‐order equal‐time correlation function, it is found that strong photon antibunching can be achieved in this system with weak excitonic nonlinearity or squeezed light via a destructive quantum interference mechanism. The optimal conditions for the photon blockade are derived analytically and discussed in details. Unlike the excitonic nonlinearity, a strong photon blockade occurs with the squeezed light at total or quasitotal resonance, even in the weak coupling regime, using an OPO material with negative second‐order nonlinear susceptibility. By acting on the driving coherent pump frequency, the control of the cavity output is achieved and the scheme can serve as a tunable single‐photon emission source.

In situ observations of stratospheric HCl using three-mirror integrated cavity output spectroscopy

Abstract. Stratospheric HCl observations are an important diagnostic for the evaluation of catalytic processes that impact the ozone layer. We report here in situ balloon-borne observations of HCl employing an off-axis integrated cavity output spectrometer (OA-ICOS) fitted with a reinjection mirror. Laboratory assessments demonstrated that the spectrometer has a 90 % response time of 10 s to changes in HCl and a 30 s precision of 26 pptv. The instrument was deployed alongside an ozone instrument in August 2018 on a balloon-borne descent between 20–80 hPa (29–18 km altitude). The observations agreed with nearby satellite measurements made by the Earth Observing System Microwave Limb Sounder within 10 % on average. This is the first time that stratospheric measurements of HCl have been made with ICOS and the first time any cavity-enhanced HCl instrument has been tested in flight.

Design and real-time control of the OPD from 20 to 200°C in a cat's-eye cavity using thick slabs of Yb3+: YAG for athermal amplification

We demonstrate an athermal, 100 mJ-energy class Yb3+: YAG slab-based amplifier designed to operate in the range of temperatures from 20 to 200°C. The gain medium consists of an edge-pumped, thick slab with a folded laser beam-path, which is defined in a cat's eye cavity thanks to 6–12 elementary paths. Highly variable operating conditions are investigated, in a close connection with the induction of severe thermal penalties in the slab. These penalties concern the material's spectroscopic properties and the thermo-mechanical distortions, at the location of the laser faces. Looking at the shape of the optical-path-difference (OPD) along the slab, we evidence a strong dependency with the pump-dependent temperature cartography inside. This involves comprehensive fits between the measurement data and Finite Element Modeling (FEM) results. As a follow-up, by closely coupling a movable cylindrical lens along the slab, we validate the efficiency of an easy-to-implement correction process to cancel the OPD in the real time. Regardless of the operating regime, this enables fully updatable lasing conditions with reduced output beam distortions in the far field of the cavity output.

Simultaneous detection of hydrogen sulfide and carbon dioxide based on off‐axis integrated cavity output spectroscopy using a near‐infrared distributed feedback diode laser

AbstractAn optical scheme for simultaneous detection of hydrogen sulfide (H2S) and carbon dioxide (CO2) is demonstrated. A near infrared tunable diode laser operating at 1.578 μm including the absorption lines of H2S at 6336.62 cm−1 and CO2 at 6336.24 cm−1 was used as the light source for spectroscopic measurements of H2S and CO2. A high‐finesse cavity with a base length of 21 cm and a pair of high reflectivity mirrors with a reflectivity of 99.999% were employed based on off‐axis integrated cavity output spectroscopy. Allan variance analysis shows that the minimum detection limits of 150 ppbv for H2S in 170 s averaging time and 1.03 ppmv for CO2 in 209 s, respectively.

Measurement of \u03b418O and \u03b42H of water and ethanol in wine by Off-Axis Integrated Cavity Output Spectroscopy and Isotope Ratio Mass Spectrometry

There are two officially approved methods for stable isotope analysis for wine authentication. One describes δ18O measurements of the wine water using Isotope Ratio Mass Spectrometry (IRMS), and the other one uses Deuterium-Nuclear Magnetic Resonance (2H-NMR) to measure the deuterium of the wine ethanol. Recently, off-axis integrated cavity output (laser) spectroscopy (OA-ICOS) has become an easier alternative to quantify wine water isotopes, thanks to the spectral contaminant identifier (SCI). We utilized an OA-ICOS analyser with SCI to measure the δ18O and δ2H of water in 27 wine samples without any pre-treatment. The OA-ICOS results reveal a wealth of information about the growth conditions of the wines, which shows the advantages to extend the official δ18O wine water method by δ2H that is obtained easily from OA-ICOS. We also performed high-temperature pyrolysis and chromium reduction combined with IRMS measurements to illustrate the “whole wine” isotope ratios. The δ18O results of OA-ICOS and IRMS show non-significant differences, but the δ2H results of both methods differ much more. As the δ2H difference between these two methods is mainly caused by ethanol, we investigated the possibility to deduce deuterium of wine ethanol from this difference. The results present large uncertainties and deviate from the obtained 2H-NMR results. The deviation is caused by the other constituents in the wine, and the uncertainty is due to the limited precision of the SCI-based correction, which need to improve to obtain the 2H values of ethanol as alternative for the 2H-NMR method.

Stable self-pulsing regime in a Brillouin ring fiber laser cavity

This study reports that when solving by full integration a set of coupled ordinary differential equations that describe the spatial evolution of the guided pump and Stokes powers caused by stimulated Brillouin scattering in the regime of pump depletion, a structure of regular pulses emerge from the output of a Brillouin laser cavity characterized as a stable self-pulsing regime. The dependence of this self-pulsing mechanism on the laser cavity length, the coupling factor, and the pump power is investigated revealing the existence of three regimes: no lasing, continuous, and self-pulsing. When compared to records in the scientific literature, this is the first time, to the best of the author’s knowledge, that a stable self-pulsing regime is reported theoretically. Furthermore, we also demonstrated the pumping depletion during the formation of the self-pulsing regime. These results provide not only a better understanding of the dynamics of self-pulsing regimes in a fiber laser cavity but also the possibility of unlocking the mechanisms responsible for the formation of stable pulse trains in a Brillouin fiber-ring laser.

Cavity-enhanced magnetometer with a spinor Bose–Einstein condensate

We propose a novel type of composite light–matter magnetometer based on a transversely driven multi-component Bose–Einstein condensate coupled to two distinct electromagnetic modes of a linear cavity. Above the critical pump strength, the change of the population imbalance of the condensate caused by an external magnetic field entails the change of relative photon number of the two cavity modes. Monitoring the cavity output fields thus allows for nondestructive measurement of the magnetic field in real time and we show that the sensitivity of the proposed magnetometer exhibits Heisenberg-like scaling with respect to the atom number. For state-of-the-art experimental parameters, we calculate the lower bound on the sensitivity of such a system to be of the order of fT –pT for a condensate of 104 atoms with coherence times on the order of several ms.

A novel gas sensing scheme using near-infrared multi-input multi-output off-axis integrated cavity output spectroscopy (MIMO-OA-ICOS)

We demonstrated a novel multi-input multi-output (MIMO) laser-to-cavity coupling scheme in off-axis integrated cavity output spectroscopy (OA-ICOS) for cavity mode noise suppression. Theoretical investigation was performed to explore the relation between the number of splitting beams and the MIMO parameters. Mode distribution and propagation inside the cavity was simulated. The noise suppression factor of the MIMO scheme and the noise level and dominated noise in the cavity were studied based on cavity mode simulation. Methane measurements were carried out using a dual-input dual-output (DIDO, N = 2) sensor system to validate the presented scheme, and good agreement was found between simulation and experiment.

Off-axis integrated cavity output spectroscopy for real-time methane measurements with an integrated wavelength-tunable light source

Off-axis integrated cavity output spectroscopy (OA-ICOS) is a sensitive technique for trace gas sensing. A wavelength modulated off-axis integrated cavity output spectroscopy (WM-OA-ICOS) based CH4 detection system was presented in this paper. An integrated near-infrared (NIR) light source consisting of a digital temperature controller, a current modulator and a 1.65 μm distributed feedback (DFB) laser was developed. A 50.8 mm long assembly Fabry–Perot (F-P) cavity was designed and used as the gas chamber. Wavelength modulation spectroscopy (WMS) was employed to improve the signal to noise ratio (SNR) of the system and a LabVIEW-based orthogonal lock-in amplifier was developed to extract the second harmonic (2f) signal. The experimental values of the optimum modulation parameters were determined and CH4 measurements were carried out to demonstrate the effectiveness and sensitivity of the sensor system. A quantitative characterization of long-term stability and detection sensitivity is presented. Based on Allan variance analysis, the limit of detection is 10.5 ppm when the averaging time is 30 s which can be improved easily by changing the cavity lens with higher reflectivity or increase the distance between the cavity mirrors. The sensor system was insensitive to optical alignment and can be easily serviced on site. Furthermore, this system can be further integrated by using self-developed lock-in amplifier based on our previous work, which enables the system to have good prospects in industrial field.

Mechanical squeezing in a dissipative optomechanical system with two driving tones

The squeezed state of a macroscopic mechanical oscillator can be exploited to enhance the sensitivity of precision measurements. Here, we theoretically demonstrate that the displacement squeezing of a mechanical oscillator in a dissipative optomechanical system can be generated by the use of two driving tones tuned to the first upper and lower mechanical sidebands. We find that the displacement squeezing of the mechanical oscillator is determined by the powers of the two driving tones and the temperature of the environment. Even when the temperature of the environment is as high as 20 mK, the mechanical squeezing beyond 3 dB can be achieved. Moreover, we show that the mechanical squeezing can be detected by directly measuring the cavity output spectrum.

Limit cycle phase and Goldstone mode in driven dissipative systems

In this article, we theoretically investigate the first- and second-order quantum dissipative phase transitions of a three-mode cavity with a Hubbard interaction. In both types, there is a mean-field (MF) limit cycle phase where the local U(1) symmetry and the time-translational symmetry of the Liouvillian superoperator are spontaneously broken. In MF, this spontaneous symmetry breaking manifests itself through the appearance of an unconditionally and fully squeezed state at the cavity output, connected to the well-known Goldstone mode. By employing the Wigner function formalism, hence, properly including the quantum noise, we show that away from the thermodynamic limit and within the quantum regime, fluctuations notably limit the coherence time of the Goldstone mode due to the phase diffusion. Our theoretical predictions suggest that interacting multimode photonic systems are rich, versatile test beds for investigating the crossovers between the mean-field picture and quantum phase transitions, a problem that can be investigated in various platforms including superconducting circuits, semiconductor microcavities, atomic Rydberg polaritons, and cuprite excitons.