We devise a new detection technique for mid-infrared multi-heterodyne spectroscopy. As an experimental implementation, mid-infrared light interrogates a gas sample in the 3-$μ$m region of the fundamental CH, OH, NH stretch in molecules and detection is performed in the near-infrared telecommunication region. Spectra showing 18000 resolved comb lines of 100-MHz spacing are recorded at a sensitivity close to the shot-noise limit. The demonstration adds to the unique advantages of dual-comb spectroscopy, such as potential very high resolution, negligible instrumental line width, and direct calibration of the frequency scale with an atomic clock. We also show that direct mid-infrared detection with a differential photo-detector module is beneficial in the limit of low mid-infrared average power.
We demonstrate the measurement of single-shot spectra of temporally selected micropulses from a mid-infrared (MIR) free-electron laser (FEL) by upconversion. We achieve the upconversion of FEL pulses at 11 μm using externally synchronized Nd:YAG or microchip laser pulses at 1064 nm to produce sum-frequency mixing (SFM) signals at 970 nm, which are detected by a compact CCD spectrometer without an intensifier. Our experimental system is very cost-effective, and allows us to obtain the laser spectra of selected micropulses at any temporal position within a single macropulse from an oscillator-ty…
Upconversion Dual-comb Passive Spectroscopy of Mid-IR Incoherent Light
Department of Electrical, Computer, and Energy Engineering, University of Colorado Boulder（科罗拉多大学博尔德分校电气、计算机和能源工程系）；Department of Physics, University of Colorado Boulder（科罗拉多大学博尔德分校物理系）
Coherent interconversion of signals between optical and mechanical domains is enabled by optomechanical interactions. Extreme light-matter coupling produced by confining light to nanoscale mode volumes can then access single mid-infrared (MIR) photon sensitivity. Here we utilise the infrared absorption and Raman activity of molecular vibrations in plasmonic nanocavities to demonstrate frequency upconversion. We convert λ~10 μm incoming light to visible via surface-enhanced Raman scattering (SERS) in doubly-resonant antennas that enhance upconversion by >10^10. We show >200% amplification of th…
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）
Upconversion imaging, where mid infrared (IR) photons are converted to visible and near IR photons via a nonlinear crystal and detected on cheap and high-performance Silicon detectors, is an appealing method to address the limitations of thermal sensors which are expensive, often require cooling and suffer from both limited spectral response and limited spatial resolution as well as poor sensitivity. However, phase matching severely limits the spectral bandwidth of this technique therefore requiring serial acquisitions in order to cover a large spectrum. Here, we introduce a novel upconversion…
Highly-sensitive mid-infrared upconversion detection based on external-cavity pump enhancement
State Key Laboratory of Precision Spectroscopy, East China Normal University（精密光谱科学技术国家重点实验室，华东师范大学）；Chongqing Key Laboratory of Precision Optics, Chongqing Institute of East China Normal University（精密光学重庆市重点实验室，华东理工大学重庆研究院）；Collaborative Innovation Center of Extreme Optics, Shanxi University（极端光学协同创新中心，山西大学）；School of Optical Electrical and Computer Engineering, University of Shanghai for Science and Technology（光电信息与计算机工程学院，上海理工大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Chongqing Institute for Brain and Intelligence, Guangyang Bay Laboratory（重庆脑与智能研究所，广阳湾实验室）
We present a scheme for estimating the noise-equivalent temperature difference (NETD) of frequency upconversion detectors (UCDs) that detect mid-infrared (MIR) light. In particular, this letter investigates the frequency upconversion of a periodically polarized crystal based on lithium niobate, where a mid-infrared conversion bandwidth of 220 nm can be achieved in a single poled period by a special design. Experimentally for a temperature target with a central wavelength of 7.89 μm in mid-infrared radiation, we estimated the NETD of the device to be 56 mK. Meanwhile, a direct measurement of th…
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Shanghai University（上海大学）
Mid-infrared photon counting and resolving via efficient frequency upconversion
State Key Laboratory of Precision Spectroscopy, East China Normal University（精密光谱科学技术国家重点实验室，华东师范大学）；School of Optical Electrical and Computer Engineering, University of Shanghai for Science and Technology（上海理工大学光学电气与计算机工程学院）；Jinan Institute of Quantum Technology（济南量子技术研究院）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）
We present a system for molecular spectroscopy using a broadband mid-infrared laser with near infrared detection. Difference frequency generation of a Yb:fiber femtosecond laser produced a mid-infrared (MIR) source tunable from 2100-3700 cm^-1 (2.7-4.7 microns) with average power up to 40 mW. The MIR spectrum was upconverted to near-infrared wavelengths for broadband detection using a two-dimensional dispersion imaging technique. Absorption measurements were performed over bandwidths of 240 cm^-1 (7.2 THz) with 0.048 cm^-1 (1.4 GHz) resolution, and absolute frequency scale uncertainty was bett…
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Institute of Semiconductors, Chinese Academy of Sciences（中国科学院半导体研究所）；Shanxi University（山西大学）
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Jinan Institute of Quantum Technology（济南量子技术研究院）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；University of Shanghai for Science and Technology（上海理工大学）
Passive Incoherent Ultrafast Mid-Infrared Upconversion Imaging and Its Calibration
University of Science and Technology of China（中国科学技术大学）；CAS Center for Excellence in Quantum Information and Quantum Physics, University of Science and Technology of China（中国科学技术大学量子信息科学与工程卓越中心）；Anhui Province Key Laboratory of Quantum Network, University of Science and Technology of China（中国科学技术大学安徽省量子通信与计算重点实验室）；Anhui Kunteng Quantum Technology Co. Ltd.（安徽昆腾量子技术有限公司）；National Key Laboratory of Deep Space Exploration（深空探测国家重点实验室）
As a novel technique for infrared detection, frequency upconversion has been successfully deployed in many applications. However, investigations into the noise properties of upconversion detectors (UCDs) have also received considerable attention. In this letter, we present a new noise source - second harmonic generation (SHG)-induced spontaneous parametric downconversion (SPDC) - experimentally and theoretically shown to exist in short-wavelength-pumped UCDs. We investigate the noise properties of two UCDs based on single-pass 1064 nm-pumped periodically poled LiNbO$_{3}$ bulk crystals. One UC…
Mid-infrared edge-enhanced imaging via angle-selective nonlinear filtering
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）
Wavelength stability of free-electron lasers (FELs) is one of the important parameters for various applications. In this paper we describe two different methods to diagnose the wavelength stability of a mid-infrared (MIR) FEL. The first one is based on autocorrelation which is usually used to measure the pulse duration, and the second one is based on frequency upconversion through sum-frequency mixing (SFM).
Frequency upconversion is a cornerstone of electromagnetic signal processing, analysis and detection. It is used to transfer energy and information from one frequency domain to another where transmission, modulation or detection is technically easier or more efficient. Optomechanical transduction is emerging as a flexible approach to coherent frequency upconversion; it has been successfully demonstrated for conversion from radio- and microwaves (kHz to GHz) to optical fields. Nevertheless, optomechanical transduction of multi-THz and mid-infrared signals remains an open challenge. Here, we uti…
Upconversion of infrared photons is a promising possibility to enhance solar cell efficiency by producing electricity from otherwise unused sub-band-gap photons. We present a rate equation model, and the relevant processes, in order to describe upconversion of near-infrared photons. The model considers stimulated and spontaneous processes, multi-phonon relaxation and energy transfer between neighboring ions. The input parameters for the model are experimentally determined for the material system β-NaEr0.2Y0.8F4. The determination of the transition probabilities, also known as the Einstein coef…
Direct detection of single photons at wavelengths beyond 2 microns under ambient conditions remains an outstanding technological challenge. One promising approach is frequency upconversion into the visible (VIS) or near-infrared (NIR) domain, where single photon detectors are readily available. Here, we propose a nanoscale solution based on a molecular optomechanical platform to up-convert photons from the far and mid-infrared (covering part of the THz gap) into the VIS-NIR domain. We perform a detailed analysis of its outgoing noise spectral density and conversion efficiency with a full quant…
Mid-infrared snapshot spectral imaging via nonlinear radial dispersion
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Guangyang Bay Laboratory
We report on Mid-infrared (MIR) OCT at 4 $μ$m based on collinear sum-frequency upconversion and promote the A-scan scan rate to 3 kHz. We demonstrate the increased imaging speed for two spectral realizations, one providing an axial resolution of 8.6 $μ$m, and one providing a record axial resolution of 5.8 $μ$m. Image performance is evaluated by sub-surface micro-mapping of a plastic glove and real-time monitoring of CO$_2$ in parallel with OCT imaging.
Wide-field mid-infrared hyperspectral imaging beyond video rate
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；University of Shanghai for Science and Technology（上海理工大学）
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东理工大学重庆研究院）；Shanxi University（山西大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Guangyang Bay Laboratory（广阳湾实验室）
Pulse-to-pulse spectral phase characterization of mid-infrared pulses at megahertz rates
The University of Tokyo（东京大学）；Polytechnique Montréal（蒙特利尔理工大学）；University of New Mexico（新墨西哥大学）；RIKEN Center for Advanced Photonics, RIKEN（理化学研究所先进光子中心）
State Key Laboratory of Precision Spectroscopy, and Hainan Institute, East China Normal University（精密光谱学国家重点实验室及海南研究院，华东师范大学）；Chongqing Key Laboratory of Precision Optics, Chongqing Institute of East China Normal University（精密光学重庆市重点实验室，华东理工大学重庆研究院）；Collaborative Innovation Center of Extreme Optics, Shanxi University（极端光学协同创新中心，山西大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Chongqing Institute for Brain and Intelligence, Guangyang Bay Laboratory（重庆脑与智能研究所，广阳湾实验室）
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Guangyang Bay Laboratory
Mid-infrared single-pixel imaging at the single-photon level
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Jinan Institute of Quantum Technology（济南量子技术研究院）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）
High-speed mid-infrared imaging via nonlinear multiplexed detection
East China Normal University（华东师范大学）；Hainan Institute, East China Normal University（华东师范大学海南研究院）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；University of Shanghai for Science and Technology（上海理工大学）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东理工大学重庆研究院）；Shanxi University（山西大学）；Shanghai University（上海大学）；University of Shanghai for Science and Technology（上海理工大学）
East China Normal University（华东师范大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）；Shanxi University（山西大学）；Shanghai University（上海大学）；University of Shanghai for Science and Technology（上海理工大学）
The advancement of technologies for the precise interrogation of molecules offers exciting possibilities for new studies in the realms of precision spectroscopy and quantum technologies. Experiments in these domains often address molecular vibrations in the mid-infrared (MIR) spectral region, thus generating the need for spectrally pure and accurate MIR laser sources. Quantum-cascade lasers (QCLs) have emerged as flexible sources of coherent radiation available over a wide range of MIR frequencies. Here, we demonstrate a robust approach for the simultaneous linewidth narrowing, frequency stabi…
The potential for improving the penetration depth of optical coherence tomography systems by using increasingly longer wavelength light sources has been known since the inception of the technique in the early 1990s. Nevertheless, the development of mid-infrared optical coherence tomography has long been challenged by the maturity and fidelity of optical components in this spectral region, resulting in slow acquisition, low sensitivity, and poor axial resolution. In this work, a mid-infrared spectral-domain optical coherence tomography system operating at 4 micron central wavelength with an axi…
State Key Laboratory of Precision Spectroscopy, East China Normal University（精密光谱学国家重点实验室，华东师范大学）；Chongqing Key Laboratory of Precision Optics, Chongqing Institute of East China Normal University（精密光学重庆市重点实验室，华东理工大学重庆研究院）；Collaborative Innovation Center of Extreme Optics, Shanxi University（极端光学协同创新中心，山西大学）；Chongqing Institute for Brain and Intelligence, Guangyang Bay Laboratory（脑与智能重庆研究院，广阳湾实验室）；Shanghai Research Center for Quantum Sciences（上海量子科学研究中心）；Jinan Institute of Quantum Technology（济南量子技术研究院）
Mid-Infrared Single-Photon Edge Enhanced Imaging based on Nonlinear Vortex Filtering
East China Normal University（华东师范大学）；University of Shanghai for Science and Technology（上海理工大学）；Chongqing Institute of East China Normal University（华东师范大学重庆研究院）
Laser frequency combs are coherent light sources that emit a broad spectrum consisting of discrete, evenly spaced narrow lines, each having an absolute frequency measurable within the accuracy of an atomic clock. Their development, a decade ago, in the near-infrared and visible domains has revolutionized frequency metrology with numerous windfalls into other fields such as astronomy or attosecond science. Extension of frequency comb techniques to the mid-infrared spectral region is now under exploration. Versatile mid-infrared frequency comb generators, based on novel laser gain media, nonline…
Mid-infrared high-resolution spectroscopy has proven an invaluable tool for the study of the structure and dynamics of molecules in the gas phase. The advent of frequency combs advances the frontiers of precise molecular spectroscopy. Here we demonstrate, in the important 3-μm spectral region of the fundamental CH stretch in molecules, dual-comb spectroscopy with experimental coherence times between the combs that exceed half-an-hour. Mid-infrared Fourier transform spectroscopy using two frequency combs with self-calibration of the frequency scale, negligible contribution of the instrumental l…
We demonstrate the first cavity-enhanced optical frequency comb spectroscopy in the mid-infrared wavelength region and report the sensitive real-time trace detection of hydrogen peroxide in the presence of a large amount of water. The experimental apparatus is based on a mid-infrared optical parametric oscillator synchronously pumped by a high power Yb:fiber laser, a high finesse broadband cavity, and a fast-scanning Fourier transform spectrometer with autobalancing detection. The comb spectrum with a bandwidth of 200 nm centered around 3.75 μm is simultaneously coupled to the cavity and both …
Mid-infrared (mid-IR) spectroscopy provides a way to study structures and dynamics of complicated molecules in condensed phases. Therefore, developing compact and broadband mid-IR spectrometer has been a long-standing challenge. Here, we show that a highly coherent and broadband mid-IR frequency comb can be generated by using an intra-pulse difference-frequency-generation with a train of pulses from a few-cycle Ti:Sapphire oscillator. By tightly focusing the oscillator output beam into a single-pass fan-out-type periodically-poled lithium niobate crystal and tilting the orientation of the crys…
We present Molecular Vibration Explorer, a freely accessible online database and interactive tool for exploring vibrational spectra and tensorial light-vibration coupling strengths of a large collection of thiolated molecules. The `Gold' version of the database gathers the results from density functional theory calculations on 2'800 commercially available thiol compounds linked to a gold atom, with the main motivation to screen the best molecules for THz and mid-infrared to visible upconversion. Additionally, the `Thiol' version of the database contains results for 1'900 unbound thiolated comp…
We demonstrate dual-comb spectroscopy based on difference frequency generation of frequency-agile near-infrared frequency combs, produced with the help of electro-optic modulators. The combs have a remarkably flat intensity distribution and their positions and line spacings can be selected freely by simply dialing a knob. We record, in the 3-micron region, Doppler-limited absorption spectra with resolved comb lines within milliseconds. Precise molecular line parameters are retrieved. Our technique holds promise for fast and sensitive time-resolved studies e.g. of trace gases.
We report on the development of a high-power mid-infrared frequency comb with 100 MHz repetition rate and 100 fs pulse duration. Difference frequency generation is realized between two branches derived from an Er:fiber comb, amplified separately in Yb:fiber and Er:fiber amplifiers. Average powers of 6.7 W and 14.9 W are generated in the 2.9 $μ$m idler and 1.6 $μ$m signal, respectively. With high average power, excellent beam quality, and passive carrier-envelope phase stabilization, this light source is a promising platform for generating broadband frequency combs in the far infrared, visible,…
Mid-infrared laser frequency combs are compelling sources for precise and sensitive metrology with applications in molecular spectroscopy and spectro-imaging. The infrared atmospheric window between 3-5.5 $μ$m in particular provides vital information regarding molecular composition. Using a robust, fiber-optic source of few-cycle pulses in the near-infrared, we experimentally demonstrate ultra-broad bandwidth nonlinear phenomena including harmonic and difference frequency generation in a single pass through periodically poled lithium niobate (PPLN). These $χ^{(2)}$ nonlinear optical processes …
