Mid-infrared interference coatings with excess optical loss below 10 ppm.

We present high-reflectivity substrate-transferred single-crystal GaAs/AlGaAs interference coatings at a center wavelength of 4.54 µm with record-low excess optical loss below 10 parts per million. These high-performance mirrors are realized via a novel microfabrication process that differs significantly from the production of amorphous multilayers generated via physical vapor deposition processes. This new process enables reduced scatter loss due to the low surface and interfacial roughness, while low background doping in epitaxial growth ensures strongly reduced absorption. We report on a suite of optical measurements, including cavity ring-down, transmittance spectroscopy, and direct absorption tests to reveal the optical losses for a set of prototype mirrors. In the course of these measurements, we observe a unique polarization-orientation-dependent loss mechanism which we attribute to elastic anisotropy of these strained epitaxial multilayers. A future increase in layer count and a corresponding reduction of transmittance will enable optical resonators with a finesse in excess of 100 000 in the mid-infrared spectral region, allowing for advances in high resolution spectroscopy, narrow-linewidth laser stabilization, and ultrasensitive measurements of various light-matter interactions.

Tightly locked optical frequency comb from a semiconductor disk laser.

Ultrafast semiconductor disk lasers (SDLs) passively modelocked using semiconductor saturable absorbers mirrors (SESAMs) generate optical frequency combs (OFCs) with gigahertz line spacings - a regime where solid-state and fiber lasers struggle with geometrical and Q-switching limitations. We stabilized both the frequency comb spacing and the offset without any additional external optical amplification or pulse compression. The overall noise performance is competitive with other gigahertz OFCs. A SESAM-modelocked vertical external-cavity surface-emitting laser (VECSEL) at a center wavelength around 1 µm generates 122-fs pulses with 160 mW average output power and we only needed 17-pJ pulse energy coupled into a silicon nitride (Si3N4) waveguide for supercontinuum generation (SCG) and OFC offset stabilization.

Author Correction: Watt-level 10-gigahertz solid-state laser enabled by self-defocusing nonlinearities in an aperiodically poled crystal.

The original version of this Article contained an error in Fig. 3a, in which the delay axis was incorrectly labeled in increments of 0.5 ps instead of the correct 0.2 ps. This has been corrected in both the PDF and HTML versions of the Article.

Watt-level 10-gigahertz solid-state laser enabled by self-defocusing nonlinearities in an aperiodically poled crystal.

Femtosecond modelocked lasers with multi-gigahertz pulse repetition rates are attractive sources for all applications that require individually resolvable frequency comb lines or high sampling rates. However, the modelocked laser architectures demonstrated so far have several issues, including the need for single-mode pump lasers, limited output power, Q-switching instabilities and challenging cavity geometries. Here, we introduce a technique that solves these issues. In a two-dimensionally patterned quasi-phase-matching (QPM) device, we create a large, low-loss self-defocusing nonlinearity, which simultaneously provides SESAM-assisted soliton modelocking in the normal dispersion regime and suppresses Q-switching induced damage. We demonstrate femtosecond passive modelocking at 10-GHz pulse repetition rates from a simple straight laser cavity, directly pumped by a low-cost highly spatially multimode pump diode. The 10.6-GHz Yb:CaGdAlO4 (Yb:CALGO) laser delivers 166-fs pulses at 1.2 W of average output power. This enables a new class of femtosecond modelocked diode-pumped solid-state lasers with repetition rates at 10 GHz and beyond.

Frequency comb offset detection using supercontinuum generation in silicon nitride waveguides.

We present the first direct carrier-envelope-offset (CEO) frequency detection of a modelocked laser based on supercontinuum generation (SCG) in a CMOS-compatible silicon nitride (Si(3)N(4)) waveguide. With a coherent supercontinuum spanning more than 1.5 octaves from visible to beyond telecommunication wavelengths, we achieve self-referencing of SESAM modelocked diode-pumped Yb:CALGO lasers using standard f-to-2f interferometry. We directly obtain without amplification strong CEO beat signals for both a 100-MHz and 1-GHz pulse repetition rate laser. High signal-to-noise ratios (SNR) of > 25 dB and even > 30 dB have been generated with only 30 pJ and 36 pJ of coupled pulse energy from the megahertz and gigahertz laser respectively. We compare these results to self-referencing using a commercial photonic crystal fiber and find that the required peak power for CEO beat detection with a comparable SNR is lowered by more than an order of magnitude when using a Si(3)N(4) waveguide.

SESAM modelocked Yb:CaGdAlO4 laser in the soliton modelocking regime with positive intracavity dispersion.

We demonstrate femtosecond SESAM modelocking in the near-infrared by using cascaded quadratic nonlinearities (phase-mismatched second-harmonic generation, SHG), enabling soliton modelocking in the normal dispersion regime without any dispersion compensating elements. To obtain large and negative self-phase modulation (SPM) we use an intracavity LBO crystal, whose temperature and angles are optimized with respect to SPM, nonlinear losses, and self-starting characteristics. To support femtosecond pulses, we use the very promising Yb:CaGdAlO(4) (CALGO) gain material, operated in a bulk configuration. The LBO crystal provides sufficient negative SPM to compensate for its own GDD as well as the positive GDD and SPM from the gain crystal. The modelocked laser produces pulses of 114 fs at 1050 nm, with a repetition rate of 113 MHz (average output power 1.1 W). We perform a detailed theoretical study of this soliton modelocking regime with positive GDD, which clearly indicates the important design constraints in an intuitive and systematic way. In particular, due to its importance in avoiding multi-pulsed modelocking, we examine the nonlinear loss associated with the cascading process carefully and show how it can be suppressed in practice. With this modelocking regime, it should be possible to overcome the limits faced by current state of the art modelocked lasers in terms of dispersion compensation and nonlinearity management at high powers, suppression of Q-switching in compact GHz lasers, and enabling femtosecond soliton modelocking at very high repetition rates due to the high nonlinearities accessible via cascading combined with eliminating the need for intracavity dispersion compensation.

Developing effective health and safety training materials for workers in beryllium-using industries.

OBJECTIVE: Despite reduced workplace exposures, beryllium sensitization and chronic beryllium disease still occur. Effective health and safety training is needed. METHODS: Through an Occupational Safety and Health Administration (OSHA) Targeted Topic Training grant and company partners, we developed a training program. Evaluation and validation included knowledge and training reaction assessments and training impact survey. RESULTS: We describe herein the iterative, five-pronged approach: (1) needs assessment; (2) materials development; (3) pilot-testing, evaluation, and material revisions; (4) worker training; and (5) evaluation and validation. Mean posttraining test score increased 14% (82% to 96%; P < 0.005) and were unchanged at 90-day follow-up (94%; P = 0.744). In addition, 49% reported making changes in work practices. CONCLUSIONS: The use of a five-pronged training program was effective and well received and resulted in improved work practices. These materials are available on the OSHA Web site.

Interpreting borderline BeLPT results.

BACKGROUND: The beryllium lymphocyte proliferation test (BeLPT) identifies persons sensitized to beryllium (BeS) and thus at risk for chronic beryllium disease (CBD). BeLPT test results are abnormal (AB), borderline (BL), or normal (NL). This manuscript addresses the predictive value and interpretation of BL BeLPT results. METHODS: The various three-result combinations that meet or exceed a nominal referral criteria of 1 AB + 1 BL are assessed with probability modeling and compared. RESULTS: At 2% prevalence, the three-result combinations that meet or exceed this referral criteria and associated probabilities of BeS are: (a) 1 AB + 1 BL + 1 NL (72%); (b) 3 BL (91%); (c) 2 AB + 1 NL (95%); (d) 1 AB + 2 BL (99%); (e) 2 AB + 1 BL (100%); and (f) 3 AB (100%). CONCLUSION: These results suggest that BL results are meaningful and that three BL results predict BeS across a broad range of population prevalences. An analysis of longitudinal BeLPT results and clinical findings from an actual surveillance program is warranted to confirm the model's predictions.

Genetic and environmental modulation of chronic obstructive pulmonary disease.

Chronic Obstructive Pulmonary Disease (COPD) is a leading cause of morbidity and mortality throughout a large part of the western world. Although personal tobacco use has been implicated in a large number of these cases, it is also true that only a fraction of smokers ever develop respiratory problems. Therefore, the question of host susceptibility and other environmental factors should be considered. This paper will briefly review evidence for host susceptibility to COPD, review evidence for additional environmental risk factors for the development of COPD, and give an example of environmental interactions with a known genetic risk factor that further increase the risk of COPD.

Occupational exposure risks in individuals with PI*Z alpha(1)-antitrypsin deficiency.

We obtained questionnaire and spirometry data from 128 alpha(1)-antitrypsin (alpha(1)AT)-deficient individuals with phenotype PI*Z to examine the relationship between chronic respiratory symptoms, airflow limitation, treatment requirements, and semiquantitative estimates of occupational exposure to dust, fumes, smoke, and gas. After adjusting for age, smoking, and prior lower respiratory tract infections, increased prevalence of chronic cough (OR = 4.69, 95% CI = 1.57-13.74, p = 0.006) and having left a job due to breathlessness (OR = 2.72, 95% CI = 1.07-6.92, p = 0.036) were seen in individuals reporting high mineral dust exposure compared with those with no exposure. Subjects reporting high mineral dust exposure also had significantly lower FEV(1) (31% predicted for high exposure versus 36% for low and 40% for unexposed, p = 0.032). The excess risk of chronic cough seen with occupational fumes or smoke exposure disappeared after adjusting for mineral dust exposure, but the association with lower FEV(1)/FVC ratio persisted (p = 0.022). Personal tobacco use was a significant risk factor for most outcome measures, but no interaction with occupational exposure was seen. These results suggest that occupational inhalational exposures are independently associated with respiratory symptoms and airflow limitation in severely alpha(1)AT-deficient individuals.

Recurring ventriculitis due to Citrobacter diversus: clinical and bacteriologic analysis.

Neonatal meningitis due to Citrobacter diversus is usually accompanied by the development of brain abscesses and tends to have high rates of morbidity and mortality. We report a case of a newborn with C. diversus meningitis and brain abscesses who relapsed after initial antibiotic therapy and from whom C. diversus was recovered from cerebrospinal fluid 4 years later during a neurosurgical procedure. Genetic differences in the early and late isolates were discovered, and explanations for this phenomenon are suggested. Possible mechanisms for prolonged persistence in the central nervous system are explored. This unusual case and the analysis of the organisms illustrate the unique features of C. diversus as a pathogen and underscore the need for developing optimal therapeutic strategies.

Respiratory arrest after local anesthesia for outpatient cataract surgery: a dramatic but transient complication.

Retrobulbar injection of anesthetic agents is common practice before ophthalmologic procedures. Rare but life-threatening complications of this procedure include respiratory depression and coma. We present the case of a woman with complete respiratory arrest and unresponsiveness who was brought into our emergency department from a local freestanding surgical center after preoperative retrobulbar anesthetic injection. Subsequently, the pathogenesis, clinical features, and supportive treatment for this dramatic but transient complication are discussed.

A gene for rabbit synovial cell collagenase: member of a family of metalloproteinases that degrade the connective tissue matrix.

We have determined the nucleotide sequence of a collagenase mRNA from rabbit synovial cells from which the primary structure of the encoded protein was deduced. This proteinase is 51% homologous to the enzyme that activates it from the zymogen form, rabbit synovial cell activator/stromelysin. Rabbit collagenase and activator/stromelysin thus share comembership in a gene family that includes human skin collagenase; the human and rabbit metalloproteinase, activator/stromelysin; and an oncogene-induced proteinase from rat named transin. The mRNA sequence of collagenase enabled us to completely map the structure of its gene, which is 9.1 kilobases and is composed of 10 exons and 9 introns. This is the first report of the structure of a collagenase gene. We show that it has striking similarity to additional members of this metalloproteinase gene family, transin genes I and II of rat. We have further sequenced genomic DNA flanking the collagenase gene and have identified nucleic acid elements of possible importance in gene regulation.