Upconversion Detection Research Articles

Wide spectral coverage terahertz frequency up-conversion detection with organic crystal OH1

Wide spectral coverage terahertz frequency up-conversion detection with organic crystal OH1

Large Dynamic Range Spectral Measurement in Terahertz Region Based on Frequency Up-Conversion Detection via OH1 Crystal.

Terahertz spectroscopy systems, which integrate terahertz sources and detectors, have important applications in many fields such as materials science and security checking. Based on highly sensitive frequency up-conversion detection, large dynamic range spectral measurements in a terahertz region are reported. Our system realized the detection sensitivity at a 10 aJ level with a 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1) crystal and a dynamic range up to seven orders. Based on this system, we verified the validity of the spectral measurement with tests which were conducted on monohydrate glucose, anhydrous glucose and mixed tablet samples with a thickness of 0.8 mm in 1~3 THz, respectively. Also, a mini coppery elbow tube with an inner diameter of 1 mm was used for the transmission of a terahertz wave to simulate some strip biological tissue samples. By allowing terahertz to transmit through this tube filled with 0.5 g glucose powder, we successfully obtained the absorption spectrum with a minimum transmittance at the absorption peak in the order of 10-4.

Wavelength‐Selective Near‐Infrared Organic Upconversion Detectors for Miniaturized Light Detection and Visualization

AbstractUpconversion detectors monolithically combining a detection unit and a light emitting unit, enables light detection and visualization in a compact structure, promising great advances in miniaturized multifunctional optoelectronics. The detection range of upconversion detectors usually covers a broadband spectrum, limiting their use in spectroscopic fields. This work investigates two wavelength‐selective upconversion detectors made with organic semiconductors to realize narrowband near‐infrared (NIR) light detection and visualization dual function. Two non‐fullerene‐based NIR‐sensitive bulk‐heterojunctions (BHJs) are exploited to make wavelength‐selective upconversion detectors, achieving peak sensitivity at 860 and 890 nm, with full width at half maximum of 125 and 170 nm, respectively. Each NIR‐sensitive BHJ comprises a donor polymer and a non‐fullerene acceptor, both of which are selectively sensitive to NIR light. The cumulative analysis of the optical properties of the absorber and current–voltage characteristics of the device indicates that the wavelength selectivity stems mainly from the wavelength‐dependent absorption. In particular, the upconversion detectors exhibit wavelength‐selective electronic and optical dual‐readouts, which are appealing for miniaturized spectroscopic applications, including health monitoring, optical communication, and microbead imaging, paving the way for practical applications.

Mid‐Infrared Single‐Photon Compressive Spectroscopy

AbstractSensitive mid‐infrared (MIR) spectroscopy plays an indispensable role in various photon‐starved conditions. However, the detection sensitivity of conventional MIR spectrometers is severely limited by excessive noises of the involved infrared sensors, especially for multi‐pixel arrays in parallel spectral acquisition. Here, an ultra‐sensitive MIR single‐pixel spectrometer is devised and implemented, which relies on high‐fidelity spectral upconversion and wavelength‐encoding compressive measurement. Specifically, a MIR nanophotonic supercontinuum from 3.1 to 3.9 µm is nonlinearly converted to the NIR band via synchronous chirped‐pulse pumping, which facilitates both the precise spectral mapping and sensitive upconversion detection. The upconverted signal is then spatially dispersed onto a programmable digital micromirror device, before being registered by a single‐element silicon detector. Consequently, the spectral information can be deciphered from the correlation between encoded patterns and recorded measurements, which results in a spectral resolution of 0.5 under an illumination flux down to 0.01 photons nm–1 pulse–1. Moreover, faithful reconstructions at sub‐Nyquist sampling rates are demonstrated using the compressive sensing algorithm, which leads to a 95% reduction in data acquisition time. The presented single‐pixel computational spectrometer features wavelength multiplexing, high throughput, and efficient sampling, which thus paves a new way for sensitive and fast spectroscopic analysis at the single‐photon level.

High-sensitivity dual-comb and cross-comb spectroscopy across the infrared using a widely tunable and free-running optical parametric oscillator

Dual-comb spectroscopy (DCS) enables high-resolution measurements at high speeds without the trade-off between resolution and update rate inherent to mechanical delay scanning. However, high complexity and limited sensitivity remain significant challenges for DCS systems. We address these via a wavelength-tunable dual-comb optical parametric oscillator (OPO) combined with an up-conversion detection method. The OPO is tunable from 1300-1670 nm (signal) and 2700-5000 nm (idler). Spatial multiplexing in both the laser and OPO cavities creates a near-common path arrangement, enabling comb-line-resolved measurements in free-running operation. The narrow instantaneous bandwidth results in high power per comb-line up to 160 μW in the mid-infrared. Through intra-cavity up-conversion based on cross-comb spectroscopy, we leverage these power levels while overcoming the sensitivity limitations of direct mid-infrared detection. This approach yields a high signal-to-noise ratio (50.2 dB Hz1/2) and high dual-comb figure of merit (3.5 × 108 Hz1/2). This scheme enabled detecting ambient methane over a 3-meter path length in millisecond time scale.

Broadband terahertz frequency-domain emission spectroscopy of DAST with a widely tunable quasi-monochromatic source and sensitive up-conversion detection

A continuous 4–32 THz emission spectrum of organic crystal DAST is obtained through a widely tunable quasi-monochromatic terahertz source and sensitive up-conversion detection. The spectrum is characterized by a frequency resolution of ∼0.05 THz and a highest signal-to-noise ratio of ∼65 dB. Terahertz signals are detectable at room temperature even in the high absorption regions of DAST, thus most of the absorption peaks of DAST are clearly located. The results verify the findings of previous works well, including density functional theory calculations and other similar experiments. This paper provides a highly sensitive instrument for broadband terahertz spectroscopic characterization.

Detection efficiency measurement of an up-conversion single-photon detector at 3.39μm based on SPDC.

Up-conversion single-photon detector (UCSPD) is promising in weak light radiometry at mid-infrared spectrum. This paper proposed a method to measure the detection efficiency of UCSPD at 3.39μm based on the visible-infrared correlated photons generated by spontaneous parametric down-conversion (SPDC). No infrared standard light source or standard detector was used in measurement and calibration result was insensitive to ambient thermal radiation. An experimental facility was established to obtained a detection efficiency of 0.0085 with a relative uncertainty of 2.8% (k = 1). Factors affecting measuring uncertainty were analyzed and corrected. Bandwidth matching between trigger channel and channel under test is a key problem in detection efficiency calibration. By measuring the bandwidth of the trigger channel and analyzing the bandwidth of the optical elements in the channel under test, we confirm that the acceptance bandwidth of up-conversion crystal is the narrowest. The two channels meet the bandwidth matching conditions, and the detection efficiency can be obtained directly without the bandwidth correction algorithm. Measured detection efficiency agreed well with the result obtained by a continuous laser measurement facility within a difference about 4.7%.

Highly sensitive mid-infrared upconversion detection based on external-cavity pump enhancement

Highly sensitive mid-infrared upconversion detection based on external-cavity pump enhancement

Tunable and narrowband shortwave infrared light sensing enabled by dual-Fano resonance enhanced sum-frequency generation

Tunable and narrowband light detection provides a means of selectively detecting optical signals at a specific wavelength, enabling a precise tool for object identification, machine vision, spectroscopy, and so on. Simultaneous tunable and narrowband response in shortwave infrared (SWIR) detectors is critical yet still challenging. This work utilizes dual-Fano resonance enhanced sum-frequency generation in a two-layer structure comprising a silicon metasurface and a two-dimensional (2D) nonlinear GaSe layer to realize tunable and narrowband light detection in the SWIR range. The silicon metasurface affords a high-quality-factor dual-Fano resonance in the SWIR regime, which enhances the near-field optical density of the two resonant wavelengths (pump and signal) when passing through the 2D nonlinear layer, leading to drastically enhanced sum-frequency generation. The sum-frequency light at a visible wavelength that contains the information of the SWIR signal light, can then be detected by a low-noise visible detector. The tunability and selectivity in the response spectrum stem from the geometry-dependent dual-Fano resonance in the silicon metasurface, covering the 1200–1550 nm range. The upconversion detector exhibits a sub-nanometer narrowband detection with a full width at half maximum of down to ∼0.1 nm, owing to the high quality factor of the Fano resonances. This SWIR narrowband detection is one of the best performances reported so far, much narrower than commercial filter products. The peak value of the specific detectivity of 1.5 × 1012 Jones at 1256.3 nm is achieved, comparable to broadband commercial InGaAs detectors. The detector designs in this work open up the opportunity of upconversion sensors for delicate spectroscopic applications.

Broadband long-wavelength upconversion in ultra-short nonlinear crystals.

Since the inception of the second-order nonlinear frequency conversion in 1961, enhancing the inherent low conversion efficiency has been a primary objective. This goal has been successfully accomplished through the utilization of cm-long nonlinear crystals characterized by high quality and nonlinearity, coupled with versatile phase-matching strategies and high-power mixing lasers. However, the reliance on lengthy nonlinear crystals and the necessity for precise phase-matching introduce stringent tolerances on acceptance angles and spectral bandwidths for the interacting fields, thereby constraining its widespread applicability in scientific and industrial domains. This challenge is addressed by combining a broadly tunable ∼5 mW quantum cascade laser operating in the 9.5-12.5 µm range with upconversion detection in ∼100 µm long AGS crystals. Using a tightly focused continuous wave Nd:YVO4 laser with 20 mW output power and spatial filtering of the upconverted beam lead to a SNR of 55 for 50 µs averaging time sufficient for many applications.

Noise-resilient single-pixel compressive sensing with single photon counting

The fast expansion of photon detection technology has fertilized the rapid growth of single-photon sensing and imaging techniques. While promising significant advantages over their classical counterparts, they suffer from ambient and quantum noises whose effects become more pronounced at low light levels, limiting the quality of the acquired signal. Here, we study how photon-counting noises degrade a single-pixel optical classifier via compressive sensing, and how its performance can be restored by using quantum parametric mode sorting. Using modified National Institute of Standards and Technology (MNIST) handwritten digits as an example, we examine the effects of detector dark counts and in-band background noises and demonstrate the effectiveness of mode filtering and upconversion detection in addressing those issues. We achieve 94% classification accuracy in the presence of 500 times stronger in-band noise than the signal received. Our results suggest a robust and efficient approach to single photon sensing in a practical environment, where sunlight, ambient, and multiscattering noises can easily dominate the weak signal.

Quantum entanglement and interference at 3 μm.

Given the important advantages of the mid-infrared optical range (2.5 to 25 μm) for biomedical sensing, optical communications, and molecular spectroscopy, extending quantum information technology to this region is highly attractive. However, the development of mid-infrared quantum information technology is still in its infancy. Here, we report on the generation of a time-energy entangled photon pair in the mid-infrared wavelength band. By using frequency upconversion detection technology, we observe the two-photon Hong-Ou-Mandel interference and demonstrate the time-energy entanglement between twin photons at 3082 nm via the Franson-type interferometer, verifying the indistinguishability and nonlocality of the photons. This work is very promising for future applications of optical quantum technology in the mid-infrared band, which will bring more opportunities in the fields of quantum communication, precision sensing, and imaging.

Highly sensitive multi-stage terahertz parametric upconversion detection based on RbTiOPO4 crystal

Highly sensitive terahertz frequency upconversion detection was demonstrated with a RbTiOPO4 crystal. The detectable THz frequency ranges were 3.6-4.0, and 5.4-5.7 THz. The minimum detectable terahertz energy at 5.6 THz was about 0.2 fJ.

Edge-Enhanced Upconversion Detection Enabled by Spatial-Complex Amplitude Modulation on Pump Beams

Edge-Enhanced Upconversion Detection Enabled by Spatial-Complex Amplitude Modulation on Pump Beams

Quantum optical tomography based on time-resolved and mode-selective single-photon detection by femtosecond up-conversion

We developed an optical time-of-flight measurement system using a time-resolved and mode-selective up-conversion single-photon detector for acquiring tomographic images of a mouse brain. The probe and pump pulses were spectrally carved from a 100-femtosecond mode-locked fiber laser at 1556 nm using 4f systems, so that their center wavelengths were situated at either side of the phase matching band separated by 30 nm. We demonstrated a sensitivity of 111 dB which is comparable to that of shot-noise-limited optical coherence tomography and an axial resolution of 57 μm (a refractive index of 1.37) with 380 femtosecond probe and pump pulses whose average powers were 1.5 mW and 30 μW, respectively. The proposed technique will open a new way of non-contact and non-invasive three-dimensional structural imaging of biological specimens with ultraweak optical irradiation.

Highly sensitive frequency upconversion detection from 1 to 3 THz with OH1 crystal.

The wide applications of terahertz (THz) wave technology in the ∼1-3 THz range has resulted in a surge in the demand for the performance improvement of THz wave detection technique. In this study, a frequency tunable, highly sensitive frequency upconversion detection based on a 2-(3-(4-hydroxystyryl)-5,5-dime-thylcyclohex-2-enylidene) malononitrile (OH1) crystal at room temperature is demonstrated. Moreover, to effectively increase the signal-to-noise ratio in the low frequency range, a beam isolation enhancer is proposed and its effect is verified. The minimum detectable THz pulse energy reaches about 100 aJ at 1.9 THz. The frequency tuning ranging from 1 to 3 THz. Sensitivity comparison with a 4-dimethylamino-N-methyl-4-stilbazolium tosylate (DAST) crystal system shows that OH1 is a more suitable nonlinear crystal in the 1-2.4 THz range.

Ultra-sensitive mid-wavelength-infrared upconversion detector

We have proposed and experimentally demonstrated an efficient ultra-sensitive mid-wavelength-infrared (MWIR) detector using a periodically poled lithium niobate nonlinear crystal and a silicon single-photon counting module. The involved frequency upconversion technique can spectrally convert the MWIR signal photons to the short-wavelength-infrared (SWIR) region. The internal quantum efficiency (QE) of the upconversion detector (UPD) reaches 8.87% at an average pump power of 10.67 W. The noise equivalent power of the UPD is measured as 3.24×10−15W/Hz1/2 at the MWIR wavelength of 4.6μm. In addition, the long-term stability is manifested by at least 12 h of operation with a relative fluctuation in the count rates as low as 0.35%.

Thermal camera based on frequency upconversion and its noise-equivalent temperature difference characterization

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, we investigate the frequency upconversion of a periodically poled crystal based on lithium niobate, where an MIR conversion bandwidth of 220 nm can be achieved in a single-poled period by a special design. Experimentally, for an MIR radiating target at a temperature of 95°C, the NETD of the device was estimated to be 56 mK with an exposure time of 1 s. Meanwhile, a direct measurement of the NETD was performed utilizing conventional methods, which resulted in 48 mK. We also compared the NETD of our UCD with commercially available direct MIR detectors. We show that the limiting factor for further NETD reduction of our device is not primarily from the upconversion process and camera noise but from the limitations of the heat source and laser performance. Our detectors have good temperature measurement performance and can be used for a variety of applications involving temperature object identification and material structure detection.

High responsivity mid-infrared indirect detection based on nonlinear crystal BaGa4Se7

Currently, non-oxide BaGa4Se7 crystal has been demonstrated as a superior nonlinear medium for both coherent mid-infrared (MIR) generation and up-conversion detection. By bridging the desired MIR region to the well-developed near-infrared devices, the latter addresses the drawbacks of traditional direct detection. Based on our recent report, a comprehensive study is conducted on the nonlinear optical up-conversion process to achieve high responsivity. An analytical model is developed and verified through experiment. Their measurement and calculation cover the relationship between the up-converted signal and the two input lights, the acceptable angle of detection crystal, and the responsivities at a wavelength ranging from 3 to 8 µm. The dependence of responsivity on experimental factors is indicated by the model. The present study provides a theoretical reference for the calibration and optimal design of this detection system, which can also be applied to other general MIR up-conversion configurations.

Highly sensitive and ratiometric detection of nitrite in food based on upconversion-carbon dots nanosensor

Nitrite (NO2−) is extensively found in the daily dietary environment. However, consuming too much NO2− can pose serious health risks. Thus, we designed a NO2−-activated ratiometric upconversion luminescence (UCL) nanosensor which could realize NO2− detection via the inner filter effect (IFE) between NO2−-sensitive carbon dots (CDs) and upconversion nanoparticles (UCNPs). Due to the exceptional optical properties of UCNPs and the remarkable selectivity of CDs, the UCL nanosensor exhibited a good response to NO2−. By taking advantage of NIR excitation and ratiometric detection signal, the UCL nanosensor could eliminate the autofluorescence thereby increasing the detection accuracy effectively. Additionally, the UCL nanosensor proved successful in detecting NO2− quantitatively in actual samples. The UCL nanosensor provides a simple as well as sensitive sensing strategy for NO2− detection and analysis, which is anticipated to extend the utilization of upconversion detection in food safety.