Terahertz quantum cascade laser frequency combs with optical feedback.

Optical feedback exists in most laser configurations and strongly affects laser performances depending on the feedback strength, length, and phase. In this paper, we investigate the frequency comb behaviour of a semiconductor quantum cascade laser emitting around 4.2 THz with external optical feedback. A periodic evolution of the laser inter-mode beatnote from single-line to multiple-line structures is experimentally observed with a minor change of optical feedback length (phase) on the wavelength scale. The comb stability of the laser with feedback is also measured and compared with the same laser without feedback. Furthermore, our simulations reveal that the dynamical oscillations invoked by optical feedback are responsible for the measured multiple-line beatnotes. It is found that the characteristic feedback period is determined by the half wavelength of the laser, while the comb operation is maintained at most feedback length positions. Therefore, terahertz quantum cascade laser combs are robust against the minor position vibration of the feedback mirror in practice, owing to the much smaller feedback phase change than that of common near-infrared laser diodes.

Improved comb and dual-comb operation of terahertz quantum cascade lasers utilizing a symmetric thermal dissipation.

In the terahertz frequency range, the quantum cascade laser (QCL) is a suitable platform for the frequency comb and dual-comb operation. Improved comb performances have been always much in demand. In this work, by employing a symmetric thermal dissipation scheme, we report an improved frequency comb and dual-comb operation of terahertz QCLs. Two configurations of cold fingers, i.e., type A and B with asymmetric and symmetric thermal dissipation schemes, respectively, are investigated here. A finite-element thermal analysis is carried out to study the parametric effects on the thermal management of the terahertz QCL. The modeling reveals that the symmetric thermal dissipation (type B) results in a more uniform thermal conduction and lower maximum temperature in the active region of the laser, compared to the traditional asymmetric thermal dissipation scheme (type A). To verify the simulation, experiments are further performed by measuring laser performance and comb characteristics of terahertz QCLs emitting around 4.2 THz mounted on type A and type B cold fingers. The experimental results show that the symmetric thermal dissipation approach (type B) is effective for improving the comb and dual-comb operation of terahertz QCLs, which can be further widely adopted for spectroscopy, imaging, and near-field applications.

Frequency tuning behaviour of terahertz quantum cascade lasers revealed by a laser beating scheme.

In the terahertz frequency range, the commercialized spectrometers, such as the Fourier transform infrared and time domain spectroscopies, show spectral resolutions between a hundred megahertz and a few gigahertz. Therefore, the high precision frequency tuning ability of terahertz lasers cannot be revealed by these traditional spectroscopic techniques. In this work, we demonstrate a laser beating experiment to investigate the frequency tuning characteristics of terahertz quantum cascade lasers (QCLs) induced by temperature or drive current. Two terahertz QCLs emitting around 4.2 THz with identical active regions and laser dimensions (150 µm wide and 6 mm long) are employed in the beating experiment. One laser is operated as a frequency comb and the other one is driven at a lower current to emit a single frequency. To measure the beating signal, the single mode laser is used as a fast detector (laser self-detection). The laser beating scheme allows the high precision measurement of the frequency tuning of the single mode terahertz QCL. The experimental results show that in the investigated temperature and current ranges, the frequency tuning coefficients of the terahertz QCL are 6.1 MHz/0.1 K (temperature tuning) and 2.7 MHz/mA (current tuning) that cannot be revealed by a traditional terahertz spectrometer. The laser beating technique shows potential abilities in high precision linewidth measurements of narrow absorption lines and multi-channel terahertz communications.

[Effect of diabetic management modes on diabetic nephropathy: a prospective study].

OBJECTIVE: To explore the effect of "diabetes specialists-community general practitioners-community nurse co-management mode" and "diabetes specialist management mode" on diabetic nephropathy (DN) in primary medical institutions. METHODS: Patients with type 2 diabetes admitted to Quanzijie Health Clinic of Jimusar County of Xinjiang Uygur Autonomous Region from October 2017 to March 2018 were enrolled. The Patients were divided into co-management group or specialist management group according to their administrative villages. The treatment plans of the two groups were formulated with reference to the current guidelines. The subjects of the co-management group were jointly managed by a fixed team composed of diabetes specialists from Jimusar Traditional Chinese Medicine Hospital, community general practitioners and community nurses from Quanzijie Health Clinic, and required to attend diabetes education courses every month. The diabetes specialist of Jimusar Traditional Chinese Medicine Hospital was responsible for the formulation and management of the treatment plan of the research object. Follow-up was fulfilled once every 4 weeks for 24 weeks in two groups. Before and after intervention, blood glucose, blood pressure, urinary albumin/creatinine ratio (UACR), estimated glomerular filtration rate (eGFR) as well as the utilization rate of angiotensin converting enzyme inhibitors/angiotensin II receptor blocker (ACEI/ARB) were collected. RESULTS: A total of 115 patients accomplished this study with 54 patients in co-management group and 61 patients in specialist management group. After 24 weeks of intervention, fasting glucose level, postprandial glucose level 2 hours after breakfast, glycosylated hemoglobin (HbA1c), Log UACR in co-management group and specialists management group were significantly decreased compared with baseline [fasting glucose level (mmol/L): 8.06±1.92 vs. 9.16±2.83, 8.21±2.10 vs. 9.06±1.89; postprandial glucose level 2 hours after breakfast (mmol/L): 12.26±3.78 vs. 14.11±5.28, 12.47±3.63 vs. 14.00±3.88; HbA1c: 0.074±0.014 vs. 0.082±0.023, 0.076±0.014 vs. 0.081±0.016; Log UACR (mg/g): 1.63±1.56 vs. 2.25±1.44, 1.84±1.65 vs. 2.43±1.56, all P < 0.05], but there was no statistical significance between the two groups [fasting glucose level (mmol/L): -1.10±0.47 vs. -0.85±0.36, postprandial glucose level 2 hours after breakfast (mmol/L): -1.85±0.88 vs. -1.53±0.68, HbA1c: -0.008±0.004 vs. -0.006±0.003, Log UACR (mg/g): -0.61±0.29 vs. -0.59±0.29, all P < 0.05]. There were no significant changes in blood pressure, serum creatinine and eGFR in the two groups before and after intervention. There were 18 and 24 patients with hypertension in co-management group and specialist management group, respectively. The utilization rates of ACEI/ARB in both groups after intervention were significantly higher than those before intervention [88.9% (16/18) vs. 22.2% (4/18), 95.8% (23/24) vs. 29.2% (7/24), both P < 0.01]. At the end of the study, the utilization rate of ACEI/ARB was similar between the two groups [88.9% (16/18) vs. 95.8% (23/24), P > 0.05]. CONCLUSIONS: Both "diabetes specialists-community general practitioners-community nurse co-management mode" and "diabetes specialist management mode" can effectively decrease glucose levels and UACR levels of patients with type 2 diabetes as well as the standard use of antihypertensive agents, which has positive effects on the prevention and treatment on DN.

Behavior of chromium and arsenic on activated carbon.

The simultaneous adsorption of hexavalent chromium (Cr(VI)) and trivalent arsenic (As(III)) in single component and binary systems has been studied by activated carbon (AC). The capacity of Cr(VI) in the single experiment is greater than that of As(III) onto AC. The effects of various parameters like initial concentration, pH and temperature have been considered in the experiment. Cr(VI) removal is pH dependent and found to be maximum at pH 2.0. While, As(III) is found to be maximum at pH 7.0 in the single adsorption experiment. In the binary adsorption of As(III), the uptake of As(III) is generally higher than the single uptake. In the single adsorption the maximum adsorption rate of As(III) is 34% and in the binary metal mixtures the maximum adsorption rate of As(III) is 40% while the initial concentration is 5mg/L. So in the binary system the Cr(VI) and As(III) are thought to be synergistic with respect to the single As(III) situation.