Search Results (213)

In this work, we present a high-performance tapered quantum cascade laser (QCL) designed to achieve both high output power and low divergence angle. By integrating a tapered waveguide with a Fabry–Perot structure, significant improvements of tapered QCL devices in both output power and beam quality are demonstrated. The optimized 50 µm wide tapered QCL achieved a maximum output power of 2.76 W in pulsed operation with a slope efficiency of 3.52 W/A and a wall-plug efficiency (WPE) of 16.2%, while reducing the divergence angle to 13.01°. The device maintained a maximum power of 1.34 W with a WPE exceeding 8.2%, measured under room temperature and continuous wave (CW) operation. Compared to non-tapered Fabry–Perot QCLs, the tapered devices exhibited a nearly 10-fold increase in output power and over 200% improvement in WPE. This work provides a promising pathway for advancing mid-infrared laser technology, particularly for applications requiring high power, low divergence, and temperature stability. Full article

Photoacoustic spectroscopy (PAS) has become a valuable technique for trace gas detection due to its high sensitivity and potential for miniaturization. This study presents the development and evaluation of a near-infrared PAS system using a 1532 nm semiconductor laser and a multipass cell (MPC) designed to enhance the optical path and thereby improve the detection of ammonia (NH₃). The minimum detection limit was determined to be 770 ppb, with a normalized noise equivalent absorption (NNEA) coefficient of 1.07 × 10⁻⁸ W cm⁻¹ Hz⁻¹/². While competitive with similar PAS systems, these results indicate that mid-infrared technologies still offer superior detection thresholds. The findings suggest that while this near-infrared setup may not yet match the sensitivity of systems using quantum cascade lasers or QEPAS, it offers notable advantages in terms of simplicity, cost, and potential for field deployment. The system’s configuration makes it a viable and efficient tool for industrial gas monitoring and real-time environmental applications, with future improvements likely to come from transitioning to the mid-infrared region and advancing laser stabilization and miniaturization techniques. Full article

In the realm of quantum communication and photonic technologies, the extension of coherence time for photon wave packets is essential for improving system efficacy. This research introduces a methodology for measuring coherence time utilizing an unbalanced fiber interferometer, specifically designed for tunable pulse-width photon wave packets produced by cold atoms. By synchronously generating write pulses, signal light, and frequency-locking light from a single laser source, the study effectively mitigated frequency discrepancies that typically arise from the use of multiple light sources. The implementation of frequency-resolved photon counting under phase-locked conditions was accomplished through the application of polarization filtering and cascaded filtering techniques. The experimental results indicated that the periodicity of frequency shifts in interference fringe patterns diminishes as the differences in delay arm lengths increase, while fluctuations in fiber length and high-frequency laser jitter adversely affect interference visibility. Through an analysis of the correlation between delay and photon counts, the coherence time of the write laser was determined to be 2.56 µs, whereas the Stokes photons produced through interactions with cold atoms exhibited a reduced coherence time of 1.23 µs. The findings suggest that enhancements in laser bandwidth compression and fiber phase stability could further prolong the coherence time of photon wave packets generated by cold atoms, thereby providing valuable technical support for high-fidelity quantum information processing. Full article

A new hyphenated technique using thin-layer chromatography (TLC) to separate analytes in mixtures, coupled with mid-infrared (MIR) laser spectroscopy for identification and quantification, is presented. The method, which provides a means for rapid screening of analytes that is practical, low-cost, fast, robust, and reproducible, was tested using nitroaromatic and aliphatic nitro high explosives (HEs) as target analytes. HEs are anthropogenic contaminants containing an -NO₂ group. For validation of the new technique, a direct comparison of the 2,4,6-trinitrotoluene (TNT) spectrum, obtained by attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy coupled with TLC, was carried out. The MIR laser spectroscopy-based method was evaluated by calculating the analytical figures of merit regarding the calibration curves’ linearity and the method’s sensitivity and precision. The TNT spectrum obtained by the MIR laser method showed two prominent and characteristic bands of the explosive at approximately 1350 cm⁻¹ and 1550 cm⁻¹ compared to the spectrum acquired by ATR-FTIR. The detection limit calculated for TNT was 84 ng, while the quantification limit was 252 ng. Multivariate analysis was used to evaluate the spectroscopic data to identify sources of variation and determine their relation. Partial least squares (PLS) regression analysis and PLS combined with discriminant analysis (PLS-DA) were used for quantification and classification. The new technique, TLC-QCL, is amenable to a smaller footprint with further developments in MIR laser technology, making it portable for fieldwork. Full article

Kidney and renal pelvic cancer are a significant cause of cancer-related deaths, with the most common malignant kidney tumor being renal cell carcinoma (RCC). Chromophobe renal cell carcinoma is a rarer form of RCC that poses significant challenges to accurate diagnosis, as it shares many histologic features with Oncocytoma, a benign renal tumor. Biopsies for histopathological and immunohistochemical analysis have limitations in distinguishing chromophobe RCC from Oncocytoma. Syndromic cases may also have tumors with overlapping features. Techniques such as infrared (IR) spectroscopic imaging have shown promise as an alternative approach to tissue diagnostics. In this study, we propose a deep-learning-based framework for automating classification in kidney tumor tissue microarrays (TMAs) using an IR dataset. Feature selection algorithms reduce data dimensionality, followed by a deep learning classification approach. A classification accuracy of 91.3% was observed for validation data, even with the use of 13.6% of all wavelengths, thereby reducing training time by 21% compared to using the entire spectrum. Through the integration of scalable deep learning models coupled with feature selection, we have developed a classification pipeline with high predictive power, which could be integrated into a high-throughput real-time IR imaging system. This would create an advanced diagnostic tool for the detection and classification of renal tumors, namely chromophobe RCC and Oncocytoma. This may impact patient outcomes and treatment strategies. Full article

The RIN of an InAs/InP(113)B quantum-dot laser for direct- and cascade-relaxation models is investigated under the gain-switching condition via the application of an optical Gaussian pulse to an excited state. A new method is proposed to obtain RIN curves by eliminating the cross-correlation between noise sources. In this way, the noise sources are described independently and simulated with independent white Gaussian random variables. The results revealed that the RIN spectrum of both models was the same, apart from the fact that the cascade-relaxation model generated somewhat shorter pulses than the direct-relaxation model. Nevertheless, the direct-relaxation model had a lower RIN than that of the cascade-relaxation model. Excited- and ground-state carrier noises strongly affected the RIN spectrum, whereas the wetting-layer carrier noise had a negligible effect. In addition, the capture and escape times significantly affected the RIN spectrum. The output pulses had a long pulse width for both models due to the long pulse width of the ground-state photons. Nevertheless, applying an optical Gaussian pulse to an excited state reduced the RIN of both models and produced narrower gain-switched output pulses. Full article

The rapid advancement of terahertz (THz) communication systems has positioned this technology as a key enabler for next-generation telecommunication networks, including 6G, secure communications, and hybrid wireless-optical systems. This review comprehensively analyzes THz communication, emphasizing its integration with free-space optical (FSO) systems to overcome conventional bandwidth limitations. While THz-FSO technology promises ultra-high data rates, it is significantly affected by atmospheric absorption, particularly absorption beyond 500 GHz, where the attenuation exceeds 100 dB/km, which severely limits its transmission range. However, the presence of a lower-loss transmission window at 680 GHz provides an opportunity for optimized THz-FSO communication. This paper explores recent developments in high-power THz sources, such as quantum cascade lasers, photonic mixers, and free-electron lasers, which facilitate the attainment of ultra-high data rates. Additionally, adaptive optics, machine learning-based beam alignment, and low-loss materials are examined as potential solutions to mitigating signal degradation due to atmospheric absorption. The integration of THz-FSO systems with optical and radio frequency (RF) technologies is assessed within the framework of software-defined networking (SDN) and multi-band adaptive communication, enhancing their reliability and range. Furthermore, this review discusses emerging applications such as self-driving systems in 6G networks, ultra-low latency communication, holographic telepresence, and inter-satellite links. Future research directions include the use of artificial intelligence for network optimization, creating energy-efficient system designs, and quantum encryption to obtain secure THz communications. Despite the severe constraints imposed by atmospheric attenuation, the technology’s power efficiency, and the materials that are used, THz-FSO technology is promising for the field of ultra-fast and secure next-generation networks. Addressing these limitations through hybrid optical-THz architectures, AI-driven adaptation, and advanced waveguides will be critical for the full realization of THz-FSO communication in modern telecommunication infrastructures. Full article

A platform for converting near-infrared (NIR) laser power modulation into the self-mixing (SM) signal of a quantum cascade laser (QCL) operating at terahertz (THz) frequencies is introduced. This approach is based on laser feedback interferometry (LFI) with a THz QCL using a metal-coated silicon nitride trampoline membrane resonator as both the external QCL laser cavity and the mechanical coupling element of the two-laser hybrid system. We show that the membrane response can be controlled with high precision and stability both in its dynamic (i.e., piezo-electrically actuated) and static state via photothermally induced NIR laser excitation. The responsivity to nanometric external cavity variations and robustness to optical feedback of the QCL LFI apparatus allows a highly sensitive and reliable transfer of the NIR power modulation into the QCL SM voltage, with a bandwidth limited by the thermal response time of the membrane resonator. Interestingly, a dual information conversion is possible thanks to the accurate thermal tuning of the membrane resonance frequency shift and displacement. Overall, the proposed apparatus can be exploited for the precise opto-mechanical control of QCL operation with advanced applications in LFI imaging and spectroscopy and in coherent optical communication. Full article

Fourier transform infrared (FTIR) spectroscopy, coupled with machine learning (ML) analysis can be used for disease monitoring with high speed and accuracy, including the classification of mosquito samples by species, age and malaria detection. However, current FTIR instruments use low-brightness thermal light sources to generate infrared light, which limits their ability to measure complex biological samples, especially where high spatial resolution is necessary, such as for specific mosquito tissues. Moreover, these systems lack portability, which is essential for field applications. To overcome these issues, spectrometers using quantum cascade lasers (QCLs) have become an attractive alternative for building fast, and portable systems due to their high electrical-to-optical efficiency, small size, and potential for low-cost. Here, we present a QCL-based spectrometer prototype designed for large scale, low-cost, environmental field-based disease surveillance. Full article

Wet etching is the mainstream fabrication method for single-bar quantum cascade lasers (QCLs). Different etching solutions result in varying etching effects on III-V semiconductor materials. In this study, an efficient and nearly ideal etching solution ratio was proposed for simultaneously etching both InP and GaInAs/AlInAs, and the surface chemical reactions induced by each component of the etching solution during the process were investigated. Using univariate and single-component experiments, coupled with various characterization techniques such as atomic force microscopy (AFM), stylus profilometer, X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM), we found that the ratio of HBr to hydrogen peroxide significantly determines the etching rate, while the ratio of HCl to hydrogen peroxide affects the interface roughness. The aim of this study was to provide a comprehensive understanding of the effects of different etching solution components, thereby enhancing the understanding of the wet etching process for InP/GaInAs/AlInAs materials. These findings offer valuable insights into efficient QCL fabrication processes and contribute to the advancement of the field. Full article

Efficient, reliable, and low-cost mid-infrared interband cascade lasers (ICLs) are needed to meet the growing demands of many useful applications such as chemical sensing, environmental and greenhouse gas monitoring, detection of pipe leaks and explosives, food safety, medical diagnostics, and industrial process control. We review the developments and status of ICLs from a historic perspective, discuss the lessons learnt from experience, and suggest considerations for future research and development. This review endeavors to include the most representative aspects and activities of ICLs, but cannot possibly describe every contribution in the 30 years since the initiation of ICLs. We present an overall picture of the ICL architecture and connect the fundamental principle and underlying physics to future activities. Full article

External cavity quantum cascade lasers (EC-QCLs) utilizing the Littrow configuration and operating at an approximate wavelength of 8.5 μm have been successfully demonstrated in continuous wave operations at room temperature. Our work provides ideas and experimental support for the optimization of the EC-QCL which indicate optimal EC-QCL performance with an external cavity length of 25 cm and investigates the impact of various parameters, including injection current and temperature on the performance of the EC-QCL. In the absence of anti-reflection (AR) coating, the tuning range at 25 °C extends up to 103.3 cm⁻¹, while the maximum side mode suppression ratio (SMSR) reaches 30.8 dB, accompanied by a full width half maximum linewidth (FWHM) of 0.76 nm. Full article

Based on tunable diode laser absorption spectroscopy (TDLAS), a water isotopes detection system was developed to detect the isotopic abundance of water vapor in the atmosphere. A single 1483.79 cm⁻¹ quantum cascade laser (QCL) and a 3120 cm optical path multi-pass cell (MPC) were adopted in the detection system. The selected spectral range, as well as the laser technology used, is particularly interesting for the real-time monitoring of water vapor isotopes in the atmosphere. In this study, a single laser can be used to perform high-sensitivity, rapid investigations of H₂O, H₂¹⁸O, H₂¹⁷O, and HDO absorption lines. Finally, we measured the abundance values of three isotopes of water vapor in the atmosphere and compared them with data from the Global Network of Isotopes in Precipitation (GNIP) website, dedicated to exploring the possibility of in situ monitoring of H₂O isotopes in the atmosphere. Full article

Self-mixing interference in a terahertz quantum-cascade laser has been demonstrated to be suitable for the detection of weak signals scattered or reflected by the target. This technology has achieved the high-sensitivity detection of complex refractive indices, surface/interface morphologies and molecular feature spectra. Here, a set of terahertz quantum-cascade lasers with different lasing frequencies is used to inspect a tiny amount of powder concealed inside a polytetrafluoroethylene tablet by using self-mixing interferometry combined with the penetration properties of terahertz waves. Multicolor spectral images were acquired, which were synthesized by absorption contrast images obtained at different lasing frequencies. They enable the detection of the spatial distribution of hidden objects which are totally opaque in visual light and allow for them to be identified with spectral absorption characteristics. Self-mixing interference technology can also obtain phase information when a terahertz wave interacts with a tablet, showing the difference between the hidden object and surroundings from another dimension. Our research may provide a strategy for the development of terahertz multispectral imaging technology for the inspection of hidden trace residues. Full article

In this work, a highly sensitive, selective, and industrially compatible gas sensor prototype is presented. The sensor utilizes three distributed-feedback quantum cascade lasers (DFB-QCLs), employing wavelength modulation spectroscopy (WMS) for the detection of hydrogen sulfide (H₂S), methane (CH₄), methyl mercaptan (CH₃SH), and carbonyl sulfide (COS) in the spectral regions of 8.0 µm, 7.5 µm, and 4.9 µm, respectively. In addition, field-programmable gate array (FPGA) hardware is used for real-time signal generation, laser driving, signal processing, and handling industrial communication protocols. To comply with on-site safety standards, the QCL sensor prototype is housed in an industrial-grade enclosure and equipped with the necessary safety features to ensure certified operation under ATEX/IECEx regulations for hazardous and explosive environments. The system integrates an automated gas sampling and conditioning module, alongside a purge and pressurization system, with intrinsic safety electronic components, thereby enabling reliable explosion prevention and malfunction protection. Detection limits of approximately 0.3 ppmv for H₂S, 60 ppbv for CH₃SH, and 5 ppbv for COS are demonstrated. Noise-equivalent absorption sensitivity (NEAS) levels for H₂S, CH₃SH, and COS were determined to be 5.93 × 10⁻⁹, 4.65 × 10⁻⁹, and 5.24 × 10⁻¹⁰ cm⁻¹ Hz^−1/2. The suitability of the sensor prototype for simultaneous sulfur species monitoring is demonstrated in process streams of a hydrodesulphurization (HDS) and fluid catalytic cracking (FCC) unit at the project’s industrial partner, OMV AG. Full article