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Hydrogen Sensor Based on Tunable Diode Laser Absorption Spectroscopy
摘要： A laser-based hydrogen (H2) sensor using wavelength modulation spectroscopy (WMS) was developed for the contactless measurement of molecular hydrogen. The sensor uses a distributed feedback (DFB) laser to target the H2 quadrupole absorption line at 2121.8 nm. The H2 absorption line exhibited weak collisional broadening and strong collisional narrowing effects. Both effects were investigated by comparing measurements of the absorption linewidth with detailed models using different line profiles including collisional narrowing effects. The collisional broadening and narrowing parameters were determined for pure hydrogen as well as for hydrogen in nitrogen and air. The performance of the sensor was evaluated and the sensor applicability for H2 measurement in a range of 0–10 %v of H2 was demonstrated. A precision of 0.02 %v was achieved with 1 m of absorption pathlength (0.02 %v·m) and 1 s of integration time. For the optimum averaging time of 20 s, precision of 0.005 %v·m was achieved. A good linear relationship between H2 concentration and sensor response was observed. A simple and robust transmitter–receiver configuration of the sensor allows in situ installation in harsh industrial environments.
关键词： laser spectroscopy,WMS,diode laser,TDLAS,absorption spectroscopy,hydrogen sensor,hydrogen,gas sensor
更新于2025-09-11 14:15:04
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Influence of Light Coupling Configuration and Alignment on the Stability of HWG-Based Gas Sensor System for Real-Time Detection of Exhaled Carbon Dioxide
摘要： A mid-infrared tunable diode laser absorption spectroscopy (TDLAS) gas sensor based on hollow waveguide (HWG) gas cell for real-time exhaled carbon dioxide (eCO2) detection is reported. A 2.73 μm distributed feedback (DFB) laser was used to target a strong CO2 absorption line, and wavelength modulation spectroscopy (WMS) with the second harmonic (WMS-2 f ) was used to retrieve the CO2 concentration with high sensitivity. The influence of different parameters, including coupling configuration of HWG, laser-to-HWG and HWG-to-detector coupling alignment on the stability of the HWG sensor is systematically studied. The HWG eCO2 sensor showed a fast response time of 2.7s, detection limit of 17 ppmv, and measurement precision of 20.9 ppmv with a 0.54 s temporal resolution. The eCO2 concentrations changed in breath cycles were measured in real time. The Allan variance indicated that the detection limit can reach 1.7 ppmv, corresponding to a detection sensitivity of 1.3×10?8 cm?1 Hz?1/2, as the integration time increases to 26 s. This work demonstrates the performance characteristics and merits of HWG eCO2 sensor for exhaled breath analysis and potential detection for other exhaled gases.
关键词： hollow waveguide,distributed feedback laser,carbon dioxide,Tunable diode laser absorption spectroscopy
更新于2025-09-11 14:15:04
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Extremely high-brightness tapered photonic crystal diode laser with narrow-emitting aperture
摘要： High-brightness tapered photonic crystal diode lasers in the 980 nm range are investigated. The tapered lasers with a 20 μm wide light-emitting aperture achieved 2.55 W at 3.2 A. The beam quality factor M2 in the vertical and lateral directions are 1.16 and 1.48 at 2.5 A. Maximum brightness ?2 · sr at the second moment level is achieved. The devices also shows a narrow far-field of 17.1° × 6.5° in the vertical and lateral directions and a high efficiency of 53%. The proportion of the first-order mode in the lasing emission is also investigated based on the measured beam quality factor.
关键词： high-brightness,beam quality factor,far-field,tapered photonic crystal diode laser,narrow-emitting aperture
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Coherent Beam Combining of Fiber Amplifiers Seeded by Commercial Low Cost Diode
摘要： Coherent beam combining (CBC) is one of the methods for power scaling of high power lasers. In the scientific literatures a low power narrow linewidth source is used for CBC, however in this report, a low cost diode laser source (spectral bandwidth <10 MHz) is used to fabricate near diffraction-limited 300 W fiber laser with CBC method. The diode laser is amplified by a preamp fiber amplifier and then divided in to three channels. Each channel is amplified to achieve 120W output with homemade power amplifiers. A 1×3 diffractive optical element is used to combine the output of the amplifiers with ~83% efficiency. Active phase locking is achieved with the stochastic parallel gradient descent (SPGD) method. A major obstacle towards high power narrow-linewidth fiber lasers is stimulated Brillouin scattering (SBS). It has been proven that phase modulation is an effective way to suppress SBS in these kind of lasers. Applying phase modulation to a single frequency laser, splits its spectrum to many spectral lines with the same frequency spacing of the modulation frequency. In this work, we use a sinusoidal signal phase modulation (30 MHz frequency and 10 V amplitude) to suppress SBS effect. The result of this modulation on the spectrum of the laser is illustrated. The maximum achievable output power for each channel without modulation is ~40 W. However, by applying modulation SBS threshold power enhances with a factor of 3. The output power of combined beam versus pump diode current (solid line) is shown. Also the backward output power (dashed line) is illustrated. As it can be seen in the figure the maximum backward power is 110 μW which proves the SBS effect is cancelled.
关键词： stimulated Brillouin scattering,diode laser,phase modulation,Coherent beam combining,fiber amplifiers
更新于2025-09-11 14:15:04
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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Monolithic Master Oscillator with Tapered Power Amplifier Diode Laser at 1060 nm with Additional Control Section for High Power Operation
摘要： State of the art diode laser light sources for high power operation with good beam quality are distributed Bragg reflector tapered diode lasers (DBR-TPLs). These devices deliver over 10 W of spectrally narrowband emission within an almost diffraction-limited beam [1]. However, due to the integration of the tapered section into the resonator, these devices are designed that only a forward traveling wave is optimal confined and amplified. This trade-off limits the potential of these devices. One way to overcome this limitation is to move the tapered section outside of the resonator and use as a single pass power amplifier in a monolithic master oscillator power amplifier (MOPA) layout [2]–[4]. However, the benefits on the emissions characteristics, as discussed below, of these devices can diminish if multi-cavity operation occurs. In this work, we present results on recently developed monolithic MOPAs for enhanced suppression of multi-cavity operation. The MOs in these devices are 2 mm long with a 7th order DBR grating at the front- and backside and a 0.75 mm long active section in the middle. An active 0.5 mm long control section (CON) follows the MO section. Both have a ridge waveguide (RW) width of 5 μm. The PA section is 3.5 mm long and defined by the tapered p-side contact with a full angle of 6°. The 3 different layouts are depicted in Fig. 1 a). In the first layout (top) all three section are in a straight line perpendicular to the front facet. The second layout (middle) has a MO section tilted by 4° and a bent CON section and the third layout (bottom) has bent CON section and a PA section tilted by 4°. Fig. 1 a) Sketch of all three monolithic MOPA layouts. b) Optical output power (solid lines) and the peak wavelength (dots) for three different monolithic MOPAs. The straight layout is used as reference to discuss the benefits of a bent control section and either a tilted MO or tilted PA on the emission characteristics of the devices. Furthermore the influence of the control section on the emission characteristics of the devices will be presented. This includes a comparison of the optical output power, the spectra and the beam quality factor of the devices. All devices provide over 6 W of optical output power at 1060 nm within a narrow spectral bandwidth below 17 pm (spectrometer resolution limit). However the overall emission characteristics have clear differences as can be seen in Fig. 1 b). Here the optical output power and the peak wavelength are plotted in dependence of the PA current. The laser with the tilted MO layout shows a small increase in output power compared to the straight layout and a reduction of spectral mode jumps for PA currents below IPA = 8 A. For the laser with the tilted PA layout the small spectral mode jumps due to multi-cavity operation are completely suppressed but the output power is reduced by 0.5 W.
关键词： MOPA,spectral bandwidth,diode laser,monolithic master oscillator power amplifier,high power operation,beam quality
更新于2025-09-11 14:15:04
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Comparison between 940 nm Laser Diode and Topical 5 % Potassium Nitrate for Tooth Desensitization. Randomized Controlled Clinical trial
摘要： Purpose: To compare the effectiveness of two dental desensitization therapies, 940nm laser diode and potassium nitrate, in patients with dental hypersensitivity (DH) symptoms. Methods: This randomized clinical trial included 30 patients who initially underwent basic periodontal therapy and presented gingival recessions Class I and II (Miller 1985) with symptoms of DH. Subjects were randomly assigned into two groups. The first group (n = 15) received laser 940 nm application for 90 seconds on the surface of the recession and were given a tube of glycerin to be applied daily in order to avoid generating bias. Patients in the second group (n = 15) were exposed to inactive laser simulating the actual application of the laser, and they were given a desensitizing gel containing 0.5 g of potassium nitrate to be applied twice daily during 14 days. Controls were carried out at 15 minutes, 8 days, 15 days, and 4 weeks. Data obtained were filled out in an Excel table. For comparison between groups the Mann Whitney U and t student tests were used (p=0.05). Results: All patients involve in the study experienced reduction in DH (p<0.01) and differences between the two interventions performed. Conclusions: Laser and nitrate therapies were effective to manage DH after basic periodontal therapy. However, a statistically significant higher sensitivity reduction was observed in laser therapy group.
关键词： diode laser,dentinal sensitivity,periodontal disease,gingival recession,potassium nitrate
更新于2025-09-11 14:15:04
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Simultaneous two cross-sectional measurements of NH<sub>3</sub> concentration in bent pipe flow using CT-tunable diode laser absorption spectroscopy
摘要： Urea Selective Catalytic Reduction (urea SCR) system is widely used for diesel engine to reduce the emission of NOx by NH3 which is provided by a hydrolysis of urea water. Concentration distribution of NH3 in an exhaust pipe is an important factor for improvement of the SCR efficiency and prevention of NH3 slip and urea deposit. Therefore, it is necessary to measure two-dimensional (2D) concentration of NH3 in detail. The purpose of this study is to develop the real-time two cross-sectional measurements technology of NH3 concentration using the computed tomography-tunable diode laser absorption spectroscopy (CT-TDLAS). Theoretical NH3 concentration distribution which was reconstructed by CT agreed to CFD results and quadruple pipe’s results showed good resolution by 14th order reconstruction. Therefore, this method has enough resolution and accuracy for measuring the concentration distribution of NH3. And this method was employed in a bent pipe model demonstrated a urea SCR system. The experimental results of two cross-sectional 2D concentration of NH3 show differences of the concentration distribution of NH3 each cross-section and flow pattern like swirl flow. It was found that CT-TDLAS was an effective method to measure concentration distribution of NH3 and observe characteristics of flow. In addition, observing flow pattern enable to validate CFD results, and it helps to improve efficiency of after treatment system.
关键词： Urea selective catalytic reduction,NH3 concentration measurement,Exhaust aftertreatment,CT tunable diode laser absorption spectroscopy,Measurement and instrumentation
更新于2025-09-11 14:15:04
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Removal of an Extra-large Irritation Fibroma With a Combination of Diode Laser and Scalpel
摘要： Introduction: Irritation fibroma is the most common tumor like and sub mucosal reactive lesion in the oral cavity. Usually it is measured less than 1.5 cm in diameter; however in rare case it has more than 3 cm in diameter. Different kind of treatment for soft tissue lesions include scalpel excision, electrical surgery, and laser surgery. The diode laser can be more effective than conventional surgery, electrosurgery and cryosurgery in reduction of bleeding and pain. Case Report: We reported a very large irritation fibroma in right lingual side of retromolar pad which was less prone to be traumatized under local irritation, in a woman wearing maxillary complete denture and use of both diode laser and scalpel for its excision.
关键词： Diode laser,Fibroma,Excision
更新于2025-09-11 14:15:04
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Management of a Recurrent Pyogenic Granuloma of the Hard Palate with Diode Laser: A Case Report
摘要： Introduction: Pyogenic granuloma (PG) is a prevalent inflammatory hyperplasia of skin and oral mucosa which is often caused by constant low-grade local irritation, traumatic injury or hormonal factors. In many cases, gingival irritation and inflammation due to poor oral hygiene are precipitating factors. Oral PG occurs predominantly on the gingiva, but it is also encountered on the lips, tongue, buccal mucosa and rarely on the hard palate. Although surgical excision is the first choice of treatment, many other treatment modalities could be counted such as cryosurgery, sodium tetradecyl sulfate sclerotherapy, intralesional steroids, flash lamp pulsed dye laser, neodymium-doped yttrium aluminium garnet (Nd:YAG) laser, carbon dioxide (CO2) laser, erbium-doped yttrium aluminum garnet (Er:YAG) lasers and diode laser have been suggested. After surgical excision recurrence occurs up to 16% of these lesions. It is believed that recurrence ensues as a result of incomplete excision, failure to eliminate etiologic factors or repeated trauma. Case Report: A 50-year-old female was referred to the Department of Oral Surgery, Gazi University, School of Dentistry, complaining of a swelling and growth on the right side of the hard palate for four months. Patient reported a similar growth in the same area about two years earlier, which had turned out to be a PG by histopathology. The treatment plan included surgical excision of the lesion using diode laser. Results: The patient reported no pain after the surgery. She was discharged with a prescription of chlorhexidine mouthwash and necessary post-operative instructions. At 7 days follow up visit, immediate recurrence of the lesion was observed, and it was excised by diode laser with 2 mm margins at its clinical periphery, to a depth up to the periosteum, by the same operator. No recurrence or scarring was observed in 14 months follow-up. Conclusion: Although diode laser is a secure and efficient technique for the treatment of intraoral PG, in order to minimize its recurrence, the lesion should be excised with a wider margin down to the periosteum or to the causing agent. Also due to its high recurrence rate, long-term follow-up is recommended.
关键词： Diode laser,Recurrence,Pyogenic Granuloma
更新于2025-09-11 14:15:04
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Gingival melanin depigmentation by 810 nm diode laser
摘要： The color of gingiva is determined by number and size of blood vessels, thickness of epithelium, keratinization degree, and melanin pigments present in epithelium. Melanocytes, located in basal and suprabasal layers of epithelium, are the cells that produce melanin pigments which play a main role for pigmentation of gingiva. In this case series, the use of 810 nm diode laser for depigmentation of gingiva is presented. Two female patients applied with a chief complaint of “darkened gums” due to heavy smoking. In intraoral examination, diffuse melanin pigmentation was observed in both the maxilla and mandible. Under the local anesthesia, 810 nm diode laser was applied for depigmentation at 1.3 W power in continuous mode. Patients were recalled at weeks 1, 4, and 12 to evaluate the healing and recurrence rate. Both the patients had no postoperative pain or edema, and complete healing was observed at week 12. This study revealed that depigmentation with 810 nm diode laser is successful in terms of esthetics and patient comfort.
关键词： melanin,gingiva,Depigmentation,diode laser
更新于2025-09-11 14:15:04