Effects of glucagon-like peptide-1 receptor agonists on gastric mucosal visibility and retained gastric contents during EGD.

BACKGROUND AND AIMS: Glucagon-like peptide-1 receptor agonists (GLP-1RAs) are increasingly used in diabetes and obesity management. Although GLP-1RAs delay gastric emptying, their impact on visibility during EGD remains uncertain. METHODS: A 1:1 matched case-control study was conducted. Individuals undergoing EGD who were taking GLP-1RAs were matched to nonusers based on demographic characteristics and diabetes status. A validated scale (POLPREP) was used to determine gastric mucosal visibility scores. RESULTS: A total of 84 pairs (N = 168) were included. GLP-1RA users had significantly lower visibility scores, with a 2.42 times higher likelihood of lower scores compared with nonusers. In addition, GLP-1RA users had a higher incidence of retained gastric contents (13.1% vs 4.8%; adjusted odds ratio, 4.62; P = .025) and aborted procedures due to this issue. No anesthesia-related adverse events were observed. CONCLUSIONS: GLP-1RA use at the time of endoscopy exhibited higher odds of lower gastric mucosal visibility scores, retained contents, and aborted procedures. Further research is warranted.

Long-term prescribed opioid use after hospitalization or emergency department presentation among opioid naïve adults (2014-2020)-A population-based descriptive cohort study.

AIMS: The aim of this work is to describe opioid initiation and long-term use after emergency department (ED) visits or hospitalizations in New South Wales, Australia, by patient, admission and clinical characteristics. METHODS: This is a population-based cohort study, including all hospitalizations and ED visits between 2014 and 2020, linked to medicine dispensings, deaths and cancer registrations (Medicines Intelligence Data Platform), among adults with no opioid dispensings in the previous year. Outcome measures were opioid initiations (dispensed within 7 days of discharge) and long-term use (90 days of continuous exposure, 90-270 days after initiation). RESULTS: The cohort included 16 153 096 admissions by 4.2 million opioid-naïve adults; 39.0% were ED presentations without hospital admission, 16.8% hospital admissions via ED and 44.2% direct hospital admissions. Opioids were initiated post-discharge for 6.2% of ED, 8.3% of hospital via ED and 10.0% of direct hospital admissions; of these 1.0%, 2.5% and 0.5% progressed to long-term opioid use, respectively. Initiation was lowest in obstetric admissions without surgery (1.0%), and highest among trauma admissions (25.4%), obstetric admissions with surgical intervention (19.8%) and non-trauma surgical admissions (12.0%). Long-term use was highest among medical admissions via ED (3.5%), trauma admissions (2.3%) and ED alone (1.0%). From 2014 to 2020, overall opioid initiations decreased 16% from 8.7% to 7.2%, and long-term opioid use decreased 33% from 1.3% to 0.8%. CONCLUSIONS: Both opioid initiation and long-term use decreased over time; however, the higher rates of long-term use following trauma, and medical admissions via ED, warrant further surveillance. Strategies supporting appropriate prescribing and access to multidisciplinary pain services will facilitate best practice care.

Oxycodone initiation in Australia (2014-2018): Sociodemographic factors and preceding health service use.

AIMS: Oxycodone is the most commonly prescribed strong opioid in Australia. This study describes health service antecedents and sociodemographic factors associated with oxycodone initiation. METHODS: Population-based new user cohort study linking medicine dispensings, hospitalizations, emergency department visits, medical services and cancer notifications from New South Wales (NSW) for 2014-2018. New users had no dispensings of any opioid in the preceding year. We analysed health service use in the 5 days preceding initiation and proportion of people on treatment over 1 year and fitted an area-based, multivariable initiation model with sociodemographic covariates. RESULTS: Oxycodone accounted for 30% of opioid initiations. Annually, 3% of the NSW population initiated oxycodone, and 5-6% were prevalent users; the new user cohort comprised 830 963 people. Discharge from hospital (39.3%), therapeutic procedures (21.4%) and emergency department visits (19.7%) were common; a hospital admission for injury (6.0%) or a past-year history of cancer (7.2%) were less common. At 1 year after initiation, 4.6% of people were using oxycodone. In the multivariable model, new use of oxycodone increased with age and was higher for people outside major cities, for example, an incidence rate ratio of 1.43 (95% confidence interval 1.36-1.51) for inner regional areas relative to major cities; there was no evidence of variation in rates of new use by social disadvantage. CONCLUSION: About half of new oxycodone use in NSW was preceded by a recent episode of hospital care or a therapeutic procedure. Higher rates of oxycodone initiation in rural and regional areas were not explained by sociodemographic factors.

Medicine utilization studies in Australian individual-level dispensing data: A blinded, multi-center replicated analysis.

PURPOSE: Medicine dispensing data require extensive preparation when used for research and decisions during this process may lead to results that do not replicate between independent studies. We conducted an experiment to examine the impact of these decisions on results of a study measuring discontinuation, intensification, and switching in a cohort of patients initiating metformin. METHODS: Four Australian sites independently developed a HARmonized Protocol template to Enhance Reproducibility (HARPER) protocol and executed their analyses using the Australian Pharmaceutical Benefits Scheme 10% sample dataset. Each site calculated cohort size and demographics and measured treatment events including discontinuation, switch to another diabetes medicine, and intensification (addition of another diabetes medicine). Time to event and hazard ratios for associations between cohort characteristics and each event were also calculated. Concordance was assessed by measuring deviations from the calculated median of each value across the sites. RESULTS: Good agreement was found across sites for the number of initiators (median: 53 127, range: 51 848-55 273), gender (56.9% female, range: 56.8%-57.1%) and age group. Each site employed different methods for estimating days supply and used different operational definitions for the treatment events. Consequently, poor agreement was found for incidence of discontinuation (median 55%, range: 34%-67%), switching (median 3.5%, range: 1%-7%), intensification (median 8%, range: 5%-12%), time to event estimates and hazard ratios. CONCLUSIONS: Differences in analytical decisions when deriving exposure from dispensing data affect replicability. Detailed analytical protocols, such as HARPER, are critical for transparency of operational definitions and interpretations of key study parameters.

The Medicines Intelligence Data Platform: A Population-Based Data Resource From New South Wales, Australia.

BACKGROUND: The Medicines Intelligence (MedIntel) Data Platform is an anonymised linked data resource designed to generate real-world evidence on prescribed medicine use, effectiveness, safety, costs and cost-effectiveness in Australia. RESULTS: The platform comprises Medicare-eligible people who are ≥18 years and residing in New South Wales (NSW), Australia, any time during 2005-2020, with linked administrative data on dispensed prescription medicines (Pharmaceutical Benefits Scheme), health service use (Medicare Benefits Schedule), emergency department visits (NSW Emergency Department Data Collection), hospitalisations (NSW Admitted Patient Data Collection) plus death (National Death Index) and cancer registrations (NSW Cancer Registry). Data are currently available to 2022, with approval to update the cohort and data collections annually. The platform includes 7.4 million unique people across all years, covering 36.9% of the Australian adult population; the overall population increased from 4.8 M in 2005 to 6.0 M in 2020. As of 1 January 2019 (the last pre-pandemic year), the cohort had a mean age of 48.7 years (51.1% female), with most people (4.4 M, 74.7%) residing in a major city. In 2019, 4.4 M people (73.3%) were dispensed a medicine, 1.2 M (20.5%) were hospitalised, 5.3 M (89.4%) had a GP or specialist appointment, and 54 003 people died. Anti-infectives were the most prevalent medicines dispensed to the cohort in 2019 (43.1%), followed by nervous system (32.2%) and cardiovascular system medicines (30.2%). CONCLUSION: The MedIntel Data Platform creates opportunities for national and international research collaborations and enables us to address contemporary clinically- and policy-relevant research questions about quality use of medicines and health outcomes in Australia and globally.

Opioid analgesic exposure during the first trimester of pregnancy and the risk of major congenital malformations in infants: a systematic review and meta-analysis†.

BACKGROUND: Prescribed opioid analgesics are frequently used to manage pain in pregnancy. However, the available literature regarding the teratogenic potential of opioid use during pregnancy has not been systematically summarised. This systematic review and meta-analysis aimed to assess the quality of the evidence on these potential risks and calculate a pooled estimate of risk for any opioid analgesic and individual opioids. METHODS: We searched PubMed, Embase and CINAHL for published studies assessing the risk of major congenital malformations in infants following first-trimester exposure to opioid analgesics compared with a reference group, excluding studies examining opioid agonist therapy or illicit opioid use. We assessed the risk of bias using the Risk of Bias in Non-Randomised Studies of Intervention tool. We pooled adjusted risk estimates from studies rated at serious risk of bias or better in a random-effects meta-analysis. RESULTS: Of 12 identified studies, 11 were at high risk of bias (eight serious; three critical). Relative to unexposed infants, those exposed to any opioid use during the first trimester of pregnancy were not at an increased risk of major congenital malformations overall (relative risk 1.04, 95%CI 0.98-1.11); cardiovascular malformations (relative risk 1.07, 95%CI 0.96-1.20); or central nervous system malformations (relative risk 1.06, 95%CI 0.92-1.21). Raised risk estimates were observed for gastrointestinal malformations (relative risk 1.40, 95%CI 0.38-5.16) and cleft palate (relative risk 1.57, 95%CI 0.48-5.13) following any opioid exposure and atrial septal defects (relative risk 1.20, 95%CI 1.05-1.36) following codeine exposure. CONCLUSIONS: Although the meta-analysis did not indicate substantial increased risk for most malformations examined, this risk remains uncertain due to the methodological limitations of the included studies. Healthcare professionals and pharmaceutical regulators should be aware of the issues related to the quality of research in this field.

Counting what counts: assessing quality of life and its social determinants among nursing home residents with dementia.

BACKGROUND: Maximizing quality of life (QoL) is a major goal of care for people with dementia in nursing homes (NHs). Social determinants are critical for residents' QoL. However, similar to the United States and other countries, most Canadian NHs routinely monitor and publicly report quality of care, but not resident QoL and its social determinants. Therefore, we lack robust, quantitative studies evaluating the association of multiple intersecting social determinants with NH residents' QoL. The goal of this study is to address this critical knowledge gap. METHODS: We will recruit a random sample of 80 NHs from 5 Canadian provinces (Alberta, British Columbia, Manitoba, Nova Scotia, Ontario). We will stratify facilities by urban/rural location, for-profit/not-for-profit ownership, and size (above/below median number of beds among urban versus rural facilities in each province). In video-based structured interviews with care staff, we will complete QoL assessments for each of ~ 4,320 residents, using the DEMQOL-CH, a validated, feasible tool for this purpose. We will also assess resident's social determinants of QoL, using items from validated Canadian population surveys. Health and quality of care data will come from routinely collected Resident Assessment Instrument - Minimum Data Set 2.0 records. Knowledge users (health system decision makers, Alzheimer Societies, NH managers, care staff, people with dementia and their family/friend caregivers) have been involved in the design of this study, and we will partner with them throughout the study. We will share and discuss study findings with knowledge users in web-based summits with embedded focus groups. This will provide much needed data on knowledge users' interpretations, usefulness and intended use of data on NH residents' QoL and its health and social determinants. DISCUSSION: This large-scale, robust, quantitative study will address a major knowledge gap by assessing QoL and multiple intersecting social determinants of QoL among NH residents with dementia. We will also generate evidence on clusters of intersecting social determinants of QoL. This study will be a prerequisite for future studies to investigate in depth the mechanisms leading to QoL inequities in LTC, longitudinal studies to identify trajectories in QoL, and robust intervention studies aiming to reduce these inequities.

Prescription retinoid and contraception use in women in Australia: A population-based study.

BACKGROUND/OBECTIVES: Oral retinoids are teratogenic, and pregnancy avoidance is an important part of retinoid prescribing. Australia does not have a standardised pregnancy prevention programme for women using oral retinoids, and the contraception strategies for women who use oral retinoids are not well understood. The objectives were to determine trends in the use of prescription retinoids among Australian reproductive-aged women and whether women dispensed oral retinoids used contraception concomitantly. METHODS: This was a population-based study using Australian Pharmaceutical Benefits (PBS) dispensing claims for a random 10% sample of 15-44-year-old Australian women, 2013 - 2021. We described rates and annual trends in dispensing claims for PBS-listed retinoids and contraceptives. We also estimated concomitant oral retinoid and contraceptive use on the day of each retinoid dispensing and determined if there was a period of contraceptive treatment that overlapped. Estimates were then extrapolated to the national level. RESULTS: There were 1,545,800 retinoid dispensings to reproductive-aged women; 57.1% were oral retinoids. The rate of retinoid dispensing to reproductive-aged women increased annually, from 28 dispensings per 1000 population in 2013 to 41 per 1000 in 2021. The rate of oral retinoid dispensing doubled over the study period, from 14 dispensings per 1000 population in 2013 to 28 per 1000 in 2021, while topical retinoid dispensing did not change. Only 25% of oral retinoid dispensings had evidence of concomitant contraceptive use in 2021. CONCLUSIONS: Rates of oral retinoid dispensing have doubled among reproductive-aged women over the past decade. A large percentage of oral retinoid use does not appear to have concomitant contraception use, posing a risk of teratogenic effects in pregnancies.

Developing a set of emergency department performance measures to evaluate delirium care quality for older adults: a modified e-Delphi study.

BACKGROUND: Older adults are at high risk of developing delirium in the emergency department (ED); however, it is under-recognized in routine clinical care. Lack of detection and treatment is associated with poor outcomes, such as mortality. Performance measures (PMs) are needed to identify variations in quality care to help guide improvement strategies. The purpose of this study is to gain consensus on a set of quality statements and PMs that can be used to evaluate delirium care quality for older ED patients. METHODS: A 3-round modified e-Delphi study was conducted with ED clinical experts. In each round, participants rated quality statements according to the concepts of importance and actionability, then their associated PMs according to the concept of necessity (1-9 Likert scales), with the ability to comment on each. Consensus and stability were evaluated using a priori criteria using descriptive statistics. Qualitative data was examined to identify themes within and across quality statements and PMs, which went through a participant validation exercise in the final round. RESULTS: Twenty-two experts participated, 95.5% were from west or central Canada. From 10 quality statements and 24 PMs, consensus was achieved for six quality statements and 22 PMs. Qualitative data supported justification for including three quality statements and one PM that achieved consensus slightly below a priori criteria. Three overarching themes emerged from the qualitative data related to quality statement actionability. Nine quality statements, nine structure PMs, and 14 process PMs are included in the final set, addressing four areas of delirium care: screening, diagnosis, risk reduction and management. CONCLUSION: Results provide a set of quality statements and PMs that are important, actionable, and necessary to a diverse group of clinical experts. To our knowledge, this is the first known study to develop a de novo set of guideline-based quality statements and PMs to evaluate the quality of delirium care older adults receive in the ED setting.

Patterns of suboptimal antipsychotic use and misuse in Australia: What can routinely collected data tell us?

AIMS: There are increasing concerns about harms related to suboptimal antipsychotic use. Here we describe recent population-based trends in antipsychotic use and harms in Australia and identify population groups exhibiting patterns of use likely to contribute to these harms. METHODS: Using population-based data from the Australian Pharmaceutical Benefits Scheme (2015-2020), poisoning calls to the New South Wales (NSW) Poisons Information Centre (2015-2020) and poisoning deaths in all coronial records (2005-2018) in Australia, we measured trends in the prevalence of antipsychotic use and related deaths and poisonings. We applied latent class analyses to identify patterns of antipsychotic use that may contribute to harms. RESULTS: Quetiapine and olanzapine had the highest prevalence of use between 2015 and 2020. Noteworthy trends included increases of 9.1% and 30.8% in quetiapine use and poisonings, while olanzapine use decreased by 4.5% but poisonings increased by 32.7%. Quetiapine and olanzapine poisonings and related deaths had the highest rates of co-ingestion of opioids, benzodiazepines and pregabalin compared to other antipsychotics. We identified six distinct population groups using antipsychotics: (i) ongoing high-dose use with sedatives (8%), (ii) ongoing use (42%), (iii) ongoing use with analgesics and sedatives (11%), (iv) long-term low-dose use (9%), (v) sporadic use (20%) and (vi) sporadic use with analgesics (10%). CONCLUSION: Ongoing potentially suboptimal antipsychotic use and associated harms highlight the need to monitor such patterns of use, for example through prescription monitoring systems.

Changes in antidepressant use in Australia: A nationwide analysis (2015-2021).

BACKGROUND: Depression and anxiety affect 4-14% of Australians every year; symptoms may have been exacerbated during the COVID-19 pandemic. We examined recent patterns of antidepressant use in Australia in the period 2015-2021, which includes the first year of the pandemic. METHODS: We used national dispensing claims for people aged ⩾10 years to investigate annual trends in prevalent and new antidepressant use (no antidepressants dispensed in the year prior). We conducted stratified analyses by sex, age group and antidepressant class. We report outcomes from 2015 to 2019 and used time series analysis to quantify changes during the first year of the COVID-19 pandemic (March 2020-February 2021). RESULTS: In 2019, the annual prevalence of antidepressant use was 170.4 per 1000 women and 101.8 per 1000 men, an increase of 7.0% and 9.2% from 2015, respectively. New antidepressant use also increased for both sexes (3.0% for women and 4.9% for men) and across most age groups, particularly among adolescents (aged 10-17 years; 46-57%). During the first year of the COVID-19 pandemic, we observed higher than expected prevalent use (+2.2%, 95% CI = [0.3%, 4.2%]) among females, corresponding to a predicted excess of 45,217 (95% CI = [5,819, 84,614]) females dispensed antidepressants. The largest increases during the first year of the pandemic occurred among female adolescents for both prevalent (+11.7%, 95% CI = [4.1%, 20.5%]) and new antidepressant use (+15.6%, 95% CI = [8.5%, 23.7%]). CONCLUSION: Antidepressant use continues to increase in Australia overall and especially among young people. We found a differential impact of the COVID-19 pandemic in treated depression and anxiety, greater among females than males, and greater among young females than other age groups, suggesting an increased mental health burden in populations already on a trajectory of increased use of antidepressants prior to the pandemic. Reasons for these differences require further investigation.

Patterns of attention deficit hyperactivity disorder medicine use in the era of new non-stimulant medicines: A population-based study among Australian children and adults (2013-2020).

BACKGROUND AND AIMS: New therapeutic options such as lisdexamfetamine and guanfacine have recently become available for the treatment of attention deficit hyperactivity disorder. We described contemporary patterns of attention deficit hyperactivity disorder medicine use among children, adolescents and adults in Australia. METHODS: This population-based study used dispensing data for a 10% random sample of Australian residents between July 2012 and December 2020. We estimated the annual prevalence and incidence of attention deficit hyperactivity disorder medicines, second-line guanfacine use and examined concurrent medicine use of both stimulants and non-stimulants. We followed incident users for up to 5 years and analysed treatment persistence using a novel proportion of people covered method. Analyses were stratified by attention deficit hyperactivity disorder medicine, sex and age group; young children (0-5 years), children (6-12 years), adolescents (13-17 years), young adults (18-24 years) and adults (⩾25 years). RESULTS: We observed a twofold increase in the overall prevalence of attention deficit hyperactivity disorder medicine use between 2013 and 2020, from 4.9 to 9.7 per 1000 persons. Incident use also increased across all age groups and both sexes, with the most pronounced increases among adolescent females (from 1.4 to 5.3 per 1000 persons). Stimulant treatment persistence after 5 years was highest among those initiating treatment as young children (64%) and children (69%) and lowest among those initiating treatment in adolescence (19%). Concurrent use of stimulants and non-stimulants was more common among males and younger age groups. Most children (87%) initiating guanfacine had prior dispensings of attention deficit hyperactivity disorder medicines. CONCLUSION: We observed increasing attention deficit hyperactivity disorder medicine use in Australia, especially among young females. Nevertheless, treatment rates remain lower than the estimated prevalence of attention deficit hyperactivity disorder across all subpopulations. Poor long-term treatment persistence in adolescence may warrant improved clinical monitoring of attention deficit hyperactivity disorder in patients transitioning from paediatric to adult care. Reassuringly, use of newly approved guanfacine appeared to be in accordance with guidelines among children.

Changes in antibiotic prescribing following COVID-19 restrictions: Lessons for post-pandemic antibiotic stewardship.

AIMS: Public health responses to reduce SARS-CoV-2 transmission have profoundly affected the epidemiology and management of other infections. We examined the impact of COVID-19 restrictions on antibiotic dispensing in Australia. METHODS: We used national claims data to investigate antibiotic dispensing trends from November 2015 to October 2020 and whether changes reflected reductions in primary care consultations. We used interrupted time series analysis to quantify changes in monthly antibiotic dispensing and face-to-face and telehealth GP consultations and examined changes by recipient age, pharmacy State and prescriber specialty. RESULTS: Over the study period, an estimated 19 921 370 people had 125 495 137 antibiotic dispensings, 71% prescribed by GPs. Following COVID-19 restrictions, we observed a sustained 36% (95% CI: 33-40%) reduction in antibiotic dispensings from April 2020. Antibiotics recommended for managing respiratory tract infections showed large reductions (range 51-69%), whereas those recommended for non-respiratory infections were unchanged. Dispensings prescribed by GPs decreased from 63.5 per 1000 population for April-October 2019 to 37.0 per 1000 for April-October 2020. Total GP consultation rates remained stable, but from April 2020, 31% of consultations were telehealth. CONCLUSION: In a setting with a low COVID-19 incidence, restrictions were associated with a substantial reduction in community dispensings of antibiotics primarily used to treat respiratory infections, coincident with reported reductions in respiratory viral infections. Our findings are informative for post-pandemic antimicrobial stewardship and highlight the potential to reduce inappropriate prescribing by GPs and specialists for respiratory viral infections.

Influences of post-implementation factors on the sustainability, sustainment, and intra-organizational spread of complex interventions.

BACKGROUND: Complex interventions are increasingly applied to healthcare problems. Understanding of post-implementation sustainment, sustainability, and spread of interventions is limited. We examine these phenomena for a complex quality improvement initiative led by care aides in 7 care homes (long-term care homes) in Manitoba, Canada. We report on factors influencing these phenomena two years after implementation. METHODS: Data were collected in 2019 via small group interviews with unit- and care home-level managers (n = 11) from 6 of the 7 homes using the intervention. Interview participants discussed post-implementation factors that influenced continuing or abandoning core intervention elements (processes, behaviors) and key intervention benefits (outcomes, impact). Interviews were audio-recorded, transcribed verbatim, and analyzed with thematic analysis. RESULTS: Sustainment of core elements and sustainability of key benefits were observed in 5 of the 6 participating care homes. Intra-unit intervention spread occurred in 3 of 6 homes. Factors influencing sustainment, sustainability, and spread related to intervention teams, unit and care home, and the long-term care system. CONCLUSIONS: Our findings contribute understanding on the importance of micro-, meso-, and macro-level factors to sustainability of key benefits and sustainment of some core processes. Inter-unit spread relates exclusively to meso-level factors of observability and practice change institutionalization. Interventions should be developed with post-implementation sustainability in mind and measures taken to protect against influences such as workforce instability and competing internal and external demands. Design should anticipate need to adapt interventions to strengthen post-implementation traction.

Narcissism, national narcissism, COVID-19 conspiracy belief, and social media use as predictors of compliance with COVID-19 public health guidelines.

Understanding health belief models, and the variables that influence adherence to public health measures imposed by local governments and international health bodies, is crucial to slowing down the spread of the virus that causes COVID-19. Conspiracy theories about the virus have quickly spread on social media and have been linked to reluctance to comply with COVID-19 regulations. Personality traits such as narcissism and collective national narcissism have also been associated with the way we perceive severity and susceptibility to the disease. To examine this further, participants (N = 183) completed an online questionnaire measuring belief in COVID-19 conspiracies, trait narcissism, national narcissism, and social media usage. A model containing these variables was able to significantly predict adherence to COVID-19 preventative health behaviours, with higher levels of COVID-19 conspiracy belief, narcissism, and social media usage all contributing to reduced adherence to recommended COVID-19 health behaviours. The findings suggest conspiracy beliefs, narcissism, and social media play a key role in adherence to behaviours orientated towards stopping the spread of COVID-19. Governments and social media companies need to demonstrate greater awareness of the negative effects of conspiracy theories spread through social media, in addition to awareness of how these effects may be greater in more narcissistic individuals.

Double Rayleigh scattering in a digitally enhanced, all-fiber optical frequency reference.

We demonstrate a passive, all-optical fiber frequency reference using a digitally enhanced homodyne interferometric phase readout. We model the noise contributions from fiber thermal noise and the coupling of double Rayleigh scattering in a digitally enhanced homodyne interferometer. A system frequency stability of 0.1 Hz/Hz is achieved above 100 Hz, which coincides with the double Rayleigh scattering estimate and is approximately a factor of five above the thermo-dynamic noise limit.

Polarization impedance measurement cavity enhanced laser absorption spectroscopy.

We present a theoretical overview and experimental demonstration of a continuous-wave, cavity-enhanced optical absorption spectrometry method to detect molecular gas. This technique utilizes the two non-degenerate polarization modes of a birefringent cavity to obtain a zero background readout of the intra-cavity absorption. We use a double-pass equilateral triangle optical cavity design with additional feed-forward frequency noise correction to measure the R14e absorption line in the 30012←00001 band of CO2 at 1572.655 nm. We demonstrate a shot noise equivalent absorption of 3 × 10-13 cm-1 Hz-1/2.

Algebraic cancellation of inter-channel cross talk in multiplexed heterodyne interferometry.

We demonstrate the algebraic cancellation of residual phase cross talk in digitally enhanced heterodyne interferometry (DEHeI), a code division multiplexing technique for interferometric sensing. By using linear combinations of parallel decoding operations at multiple delays, we synthesize a zero correlation for spurious signals and remove phase cross talk: a method we call offset decoding. We experimentally demonstrate 70 dB of signal isolation and over 40 dB greater isolation than the equivalent standard implementation of DEHeI.

Infrasonic performance of a passively stabilized, all-fiber, optical frequency reference.

We report the infrasonic performance of a fiber optic laser frequency reference with potential application to space-based gravitational wave detectors, such as the Laser Interferometer Space Antenna. We determine the optimum cross-over frequency between an optical frequency comb stabilized to a Rubidium atomic reference and two passive, all-fiber interferometers interrogated using digitally enhanced homodyne interferometery. By measuring the relative stability between the three independent optical frequency references, we find the optimum cross-over frequency to occur at 1.5 mHz, indicating that our passive fiber frequency reference is superior to the optical frequency comb at all higher frequencies. In addition, we find our fiber interferometers achieve a stability of 20 kHz/Hz at 1.5 mHz, improving to a stability of 4 Hz/Hz above 3 Hz. These results represent an independent characterization of digitally enhanced fiber references over long time scales and provide an estimate of thermal effects on these passively isolated systems, informing future reference architectures.

Digitally enhanced molecular dispersion spectroscopy.

A frequency and intensity noise immune fiber dispersion spectrometer with a digitally enhanced homodyne phase extraction system is presented. A hydrogen cyanide (H13CN) vapor cell is placed in a digitally enhanced Sagnac interferometer, and the anomalous dispersion at the 1550.515 nm P11 transition is interrogated with a tunable laser. An analytical model of the dispersion induced phase readout shows close agreement with the experimentally obtained phase signal. Immunity to frequency and intensity noise confers sub-microradian phase sensitivity, corresponding to a spectroscopic detection limit of 77ppb×m/Hz.