Towards space-deployable laser stabilization systems based on vibration-insensitive cubic cavities with crystalline coatings.

We present the development of a transportable laser frequency stabilization system with application to both optical clocks and a next-generation gravity mission (NGGM) in space. This effort leverages a 5-cm long cubic cavity with crystalline coatings operating at room temperature and with a center wavelength of 1064 nm. The cavity is integrated in a custom vacuum chamber with dedicated low-noise locking electronics. Our vacuum-mounted cavity and control system are well suited for space applications, exhibiting state-of-the-art noise performance while being resilient to radiation exposure, vibration, shock, and temperature variations. Furthermore, we demonstrate a robust means of automatically (re)locking the laser to the cavity when resonance is lost. We show that the mounted cavity is capable of reaching technology readiness level (TRL) 6, paving the way for high-performance ultrastable laser systems and eventually optical atomic clocks amenable to future satellite platforms.

Optical performance of large-area crystalline coatings.

Given their excellent optical and mechanical properties, substrate-transferred crystalline coatings are an exciting alternative to amorphous multilayers for applications in precision interferometry. The high mechanical quality factor of these single-crystal interference coatings reduces the limiting thermal noise in precision optical instruments such as reference cavities for narrow-linewidth laser systems and interferometric gravitational wave detectors. In this manuscript, we explore the optical performance of GaAs/AlGaAs crystalline coatings transferred to 50.8-mm (2-inch) diameter fused silica and sapphire substrates. We present results for the transmission, scattering, absorption, and surface quality of these prototype samples including the defect density and micro-roughness. These novel coatings exhibit optical performance on par with state-of-the-art dielectric structures, encouraging further work focused on the fabrication of larger optics using this technique.

High-Power Growth-Robust InGaAs/InAlAs Terahertz Quantum Cascade Lasers.

We report on high-power terahertz quantum cascade lasers based on low effective electron mass InGaAs/InAlAs semiconductor heterostructures with excellent reproducibility. Growth-related asymmetries in the form of interface roughness and dopant migration play a crucial role in this material system. These bias polarity dependent phenomena are studied using a nominally symmetric active region resulting in a preferential electron transport in the growth direction. A structure based on a three-well optical phonon depletion scheme was optimized for this bias direction. Depending on the sheet doping density, the performance of this structure shows a trade-off between high maximum operating temperature and high output power. While the highest operating temperature of 155 K is observed for a moderate sheet doping density of 2 × 1010 cm-2, the highest peak output power of 151 mW is found for 7.3 × 1010 cm-2. Furthermore, by abutting a hyperhemispherical GaAs lens to a device with the highest doping level a record output power of 587 mW is achieved for double-metal waveguide structures.

Coupled cavity terahertz quantum cascade lasers with integrated emission monitoring.

We demonstrate the on-chip generation and detection of terahertz radiation in coupled cavity systems using a single semiconductor heterostructure. Multiple sections of a terahertz quantum cascade laser structure in a double-metal waveguide are optically coupled and operate either as a laser or an integrated emission monitor. A detailed analysis of the photon-assisted carrier transport in the active region below threshold reveals the detection mechanism for photons emitted by the very same structure above threshold. Configurations with a single laser cavity and two coupled laser cavities are studied. It is shown that the integrated detector can be used for spatial sensing of the light intensity within a coupled cavity.

Patient-centered psoriatic arthritis (PsA) activity assessment by Stockerau Activity Score for Psoriatic Arthritis (SASPA).

BACKGROUND: To investigate whether a modified Rheumatoid Arthritis Disease Activity Index-5 could be applied as a routine assessment tool for psoriatic arthritis (PsA) patients. METHODS: Ninety-seven PsA outpatients (mean age 49.78 years; age range 23-80 years; 49 male, 48 female), completed a prototype questionnaire. Tender and swollen joint counts, including enthesiopathy, physician's assessment of disease activity on a visual analog scale (MDglob), erythrocyte sedimentation rate, and patient satisfaction with disease status (PatSat: 1 = excellent to 5 = unsatisfactory) were recorded. Factorial analysis was performed and alpha, as a measure of reliability, and tau were calculated. The ultimate five-item questionnaire, calculated by (Q1 + Q2 + Q3 + Q4 + Q5)/5, was then handed over to 152 PsA outpatients (mean age 54.02 years; age range 26-80 years; 82 male, 70 female), and analyzed accordingly. RESULTS: Analyzing the internal consistency of the prototype questionnaire revealed the highest alpha value of 0.849, on deleting the question targeting disease course. Alpha for the final Stockerau Activity Score for Psoriatic Arthritis (SASPA) was 0.875, with all items contributing to the final result (item loading from 0.573 to 0.910). Kendall's tau for the relationship between SASPA scores and swollen joint count, tender joint count, and MDglob was 0.34, 0.416, and 0.392, respectively. The sensitivity of the questionnaire to change was demonstrated in patients starting treatment with a tumor necrosis factor blocker (standardized mean difference: 2.1). CONCLUSION: The SASPA questionnaire constitutes a fully patient-administered tool to monitor PsA activity. Its reliability, convergent validity, and sensitivity to change were demonstrated.

Subwavelength micropillar array terahertz lasers.

We report on micropillar-based terahertz lasers with active pillars that are much smaller than the emission wavelength. These micropillar array lasers correspond to scaled-down band-edge photonic crystal lasers forming an active photonic metamaterial. In contrast to photonic crystal lasers which use significantly larger pillar structures, lasing emission is not observed close to high-symmetry points in the photonic band diagram, but in the effective medium regime. We measure stimulated emission at 4 THz for micropillar array lasers with pillar diameters of 5 µm. Our results not only demonstrate the integration of active subwavelength optics in a terahertz laser, but are also an important step towards the realization of nanowire-based terahertz lasers.

Probing scattering mechanisms with symmetric quantum cascade lasers.

A characteristic feature of quantum cascade lasers is their unipolar carrier transport. We exploit this feature and realize nominally symmetric active regions for terahertz quantum cascade lasers, which should yield equal performance with either bias polarity. However, symmetric devices exhibit a strongly bias polarity dependent performance due to growth direction asymmetries, making them an ideal tool to study the related scattering mechanisms. In the case of an InGaAs/GaAsSb heterostructure, the pronounced interface asymmetry leads to a significantly better performance with negative bias polarity and can even lead to unidirectionally working devices, although the nominal band structure is symmetric. The results are a direct experimental proof that interface roughness scattering has a major impact on transport/lasing performance.

Terahertz active photonic crystals for condensed gas sensing.

The terahertz (THz) spectral region, covering frequencies from 1 to 10 THz, is highly interesting for chemical sensing. The energy of rotational and vibrational transitions of molecules lies within this frequency range. Therefore, chemical fingerprints can be derived, allowing for a simple detection scheme. Here, we present an optical sensor based on active photonic crystals (PhCs), i.e., the pillars are fabricated directly from an active THz quantum-cascade laser medium. The individual pillars are pumped electrically leading to laser emission at cryogenic temperatures. There is no need to couple light into the resonant structure because the PhC itself is used as the light source. An injected gas changes the resonance condition of the PhC and thereby the laser emission frequency. We achieve an experimental frequency shift of 10(-3) times the center lasing frequency. The minimum detectable refractive index change is 1.6 × 10(-5) RIU.

Gain and losses in THz quantum cascade laser with metal-metal waveguide.

Coupling of broadband terahertz pulses into metal-metal terahertz quantum cascade lasers is presented. Mode matched terahertz transients are generated on the quantum cascade laser facet of subwavelength dimension. This method provides a full overlap of optical mode and active laser medium. A longitudinal optical-phonon depletion based active region design is investigated in a coupled cavity configuration. Modulation experiments reveal spectral gain and (broadband) losses. The observed gain shows high dynamic behavior when switching from loss to gain around threshold and is clamped at total laser losses.

A comparison of patient questionnaires and composite indexes in routine care of rheumatoid arthritis patients.

OBJECTIVE: To evaluate the agreement between the Routine Assessment of Patient Index Data 3 (RAPID-3) and a modified version of the Rheumatoid Arthritis Disease Activity Index (RADAI-5), as well as the Disease Activity Score including a 28 joint count (DAS28-ESR) and the Clinical Disease Activity Index (CDAI) in daily routine. METHODS: One hundred and twenty-eight rheumatoid arthritis (RA) out-patients completed the RADAI-5 and the RAPID-3. Simultaneously, the DAS28-ESR and the CDAI were applied. Cronbach's Alpha as a measure for reliability was calculated and factorial analysis was performed. For agreement analysis, Kendall's Tau was calculated. RESULTS: Time to score the questionnaires was 25seconds. The median RADAI-5 was 2.8 (0-9.2), the median RAPID-3 3.3 (0-8.6), the median DAS28-ESR 2.95 (0.43-6.24), and the median CDAI 5.6 (0-37.5). Cronbach's Alpha for the RADAI-5 was 0.906 and 0.871 for the RAPID-3, however, only 0.165 for the DAS28-ESR and 0.210 for the CDAI, respectively. Factorial analysis revealed that both questionnaires and the DAS28-ESR, but not the CDAI, constitute mono-dimensional instruments. Tau for the agreement between the RADAI-5 and the RAPID-3 appeared to be 0.587 (p<0.001), and to be 0.582 (p<0.001) between the DAS28-ESR and the CDAI, while it was lower for the relationship between the questionnaires and the composite indexes. CONCLUSION: Reliability of the RAPID-3 and RADAI-5 was significantly higher than of the indexes. The questionnaires as well as the indexes proved to be in highly moderate agreement, while agreement between the questionnaires and the indexes appeared to be lower.

The rheumatoid arthritis disease activity index-5 in daily use. Proposal for disease activity categories.

OBJECTIVE: To establish thresholds for rheumatoid arthritis (RA) activity categories according to the RA Disease Activity Index-5 (RADAI-5). METHODS: Three hundred ninety-two patients with RA were categorized according to Disease Activity Score 28-joint count (DAS28), Clinical Disease Activity Index (CDAI), and their satisfaction (PATSAT) with disease status. These measures built the basis for the calculation of disease activity limits for the RADAI-5. Patient assessments simultaneously meeting the identical DAS28, CDAI, and PATSAT categories were taken as the references to establish the thresholds for the respective RADAI-5 categories by calculating the third quartile of the corresponding RADAI-5 values. Subsequently, these new thresholds were applied to all assessments. RESULTS: Seven hundred fifty-eight assessments in 392 patients (2 assessments median/patient) could be obtained, most patients having mild to moderate disease according to DAS28 and CDAI. Calculating the third quartile, the RADAI-5 thresholds were as follows: 0.0-1.4 for a remission-like state, 1.6-3.0 for mild disease activity, 3.2-5.4 for moderate, and 5.6-10.0 for high disease activity. Categorization according to the RADAI-5 showed a normal distribution, while DAS28 and CDAI were somewhat shifted to the left. DAS28 and CDAI levels, as well as tender and swollen joint counts and physician's global assessment and erythrocyte sedimentation rate, proved to be highly significantly different within the different RADAI-5 categories (Kruskal-Wallis test p < 0.001). CONCLUSION: RADAI-5 thresholds for RA activity could be elaborated. Patient self-report questionnaires may substitute composite disease activity scores and may contribute significantly to improving documentation in routine patient care.