High power, broad tuning quantum cascade laser at λ ∼ 8.9 µm.

Many molecules have broad fingerprint absorption spectra in mid-wave infrared range which requires broadly tunable lasers to cover the interested spectrum in one scan. We report a strain-balanced, InAlAs/InGaAs/InP quantum cascade laser structure based on diagonal transition active region with high output power and and wide tuning range at λ ∼ 8.9 µm. The maximum pulsed optical power and the wall-plug efficiency at room temperature are 4 W and 11.7%, respectively. Maximum continuous wave double-facet power is 1.2 W at 25 °C for a 4 mm by 9 µm laser mounted epi-side down on a diamond/copper composite submount. The maximum pulsed and continuous wave external-cavity tuning range are from 7.71 µm to 9.15 µm and from 8 µm to 8.9 µm, respectively. The continuous wave power of the external cavity mode exceeds 200 mW across the entire spectrum.

Low voltage-defect quantum cascade lasers based on excited-states injection at λ ∼ 8.5 µm.

A quantum cascade laser emitting at λ∼8.5 µm based on the excited-state injection is presented. The operating voltage is reduced for a low-voltage defect in the excited-state design, compared with the conventional ground-state injection design. The threshold voltage and voltage defect are as low as 6.3 V and 54 mV for a 30-stage active region, respectively. Devices were fabricated through standard buried-heterostructure processing to decrease the heat accumulation. A continuous-wave optical power of 340 mW is obtained at 283 K with a threshold current density of 2.7 kA/cm2. Such a design has the potential to further improve the wall plug efficiency for increased voltage efficiency.

Safety of an inactivated SARS-CoV-2 vaccine among healthcare workers in China.

Background: Although the inactivated SARS-CoV-2 vaccine (CoronaVac) has undergone preclinical tests and clinical trials evaluating its efficacy and safety, few data have been reported in the post-licensure real-world setting. We aimed to assess the safety of the vaccine among healthcare workers.Methods: A self-administered online survey on monitoring adverse reactions post vaccination was conducted among the staff who worked at and were vaccinated in a tertiary hospital in Taizhou, China, from February 24 to 7 March 2021. A total of 1526 subjects responded to the questionnaire when they received an e-mail or an e-poster on WeChat.Results: The incidences of overall adverse reactions after the first and second injections were 15.6% (238/1526) and 14.6% (204/1397), respectively. The most common adverse reaction was localized pain at the injection site, with an incidence of 9.6% and 10.7% after each dose, accounting for 61.8% and 73.0% of adverse reactions, respectively. Fatigue, muscle pain, and headache were the most common systemic adverse reactions.Conclusions: These findings implied that the inactivated CoronaVac vaccine has an acceptable safety profile among healthcare workers due to the low incidence of self-reported adverse reactions. This may boost public confidence in nationwide mass vaccination campaigns.

Anomalous Mode Transitions in High Power Distributed Bragg Reflector Quantum Cascade Lasers.

In this paper, an anomalous spectral data of distributed Bragg reflector (DBR) quantum cascade lasers (QCLs) emitting around 7.6 µm is presented. The two-section DBR lasers, consisting of a gain section and an unpumped Bragg reflector, display an output power above 0.6 W in continuous wave (CW) mode at room temperature. The anomalous spectral data is defined as a longitudinal mode which moves toward shorter wavelengths with increasing temperature or injection current, which is unexpected. Although the longer wavelength modes are expected to start lasing when raising device temperature or injection current, occasional mode hops to a shorter wavelength are seen. These anomalous mode transitions are explained by means of modal analysis. The thermal-induced change of the refractive index implied by an increase in the temperature or injection current yields nearly periodic transitions between cavity modes.

Demonstration of High-Power and Stable Single-Mode in a Quantum Cascade Laser Using Buried Sampled Grating.

High-power, low-threshold stable single-mode operation buried distributed feedback quantum cascade laser by incorporating sampled grating emitting at λ ~ 4.87 µm is demonstrated. The high continuous wave (CW) output power of 948 mW and 649 mW for a 6-mm and 4-mm cavity length is obtained at 20 °C, respectively, which benefits from the optimized optical field distribution of sampled grating. The single-mode yields of the devices are obviously enhanced by controlling cleaved positions of the two end facets precisely. As a result, stable single-mode emission and mode tuning linearly without any mode hopping of devices are obtained under the different heat sink temperatures or high injection currents.

Tapered Quantum Cascade Laser Arrays Integrated with Talbot Cavities.

Power scaling in broad area quantum cascade laser (QCL) usually leads to the deterioration of the beam quality with an emission of multiple lobes far-field pattern. In this letter, we demonstrate a tapered QCL array integrated with Talbot cavity at one side of the array. Fundamental supermode operation is achieved in the arrays with taper straight-end connected to the Talbot cavity. Lateral far-field of the fundamental supermode shows a near diffraction limited beam divergence of 2.7°. The output power of a five-element array is about three times as high as a single-ridge laser with an emission wavelength of around 4.8 µm. However, arrays with the taper-end connected to the Talbot cavity always show a high-order supermode operation whatever Talbot cavity length is.

Stable Single-Mode Operation of Distributed Feedback Quantum Cascade Laser by Optimized Reflectivity Facet Coatings.

In this work, quantum cascade lasers (QCLs) based on strain compensation combined with two-phonon resonance design are presented. Distributed feedback (DFB) laser emitting at ~ 4.76 µm was fabricated through a standard buried first-order grating and buried heterostructure (BH) processing. Stable single-mode emission is achieved under all injection currents and temperature conditions without any mode hop by the optimized antireflection (AR) coating on the front facet. The AR coating consists of a double layer dielectric of Al2O3 and Ge. For a 2-mm laser cavity, the maximum output power of the AR-coated DFB-QCL was more than 170 mW at 20 °C with a high wall-plug efficiency (WPE) of 4.7% in a continuous-wave (CW) mode.