Perioperative mortality in bariatric surgery: meta-analysis.

BACKGROUND: Bariatric surgery is an established treatment for severe obesity; however, fewer than 1 per cent of eligible patients undergo surgery. The perceived risk of surgery may contribute to the low uptake. The aim of this study was to determine perioperative mortality associated with bariatric surgery, comparing different operation types and data sources. METHODS: A literature search of Ovid MEDLINE, Embase, and the Cochrane Central Register of Controlled Trials was conducted to identify studies published between 1 January 2014 and 31 July 2020. Inclusion criteria were studies of at least 1000 patients reporting short-term mortality after bariatric surgery. Data were collected on RCTs. Meta-analysis was performed to establish overall mortality rates across different study types. The primary outcome measure was perioperative mortality. Different operation types were compared, along with study type, in subgroup analyses. The study was registered at PROSPERO (2019: CRD 42019131632). RESULTS: Some 4356 articles were identified and 58 met the inclusion criteria. Data were available on over 3.6 million patients. There were 4707 deaths. Pooled analysis showed an overall mortality rate of 0.08 (95 per cent c.i. 0.06 to 0.10; 95 per cent prediction interval 0 to 0.21) per cent. In subgroup analysis, there was no statistically significant difference between overall, 30-day, 90-day or in-hospital mortality (P = 0.29). There was no significant difference in reported mortality for RCTs, large studies, national databases or registries (P = 0.60). The pooled mortality rates by procedure type in ascending order were: 0.03 per cent for gastric band, 0.05 per cent for sleeve gastrectomy, 0.09 per cent for one-anastomosis gastric bypass, 0.09 per cent for Roux-en-Y gastric bypass, and 0.41 per cent for duodenal switch (P < 0.001 between operations). CONCLUSION: Bariatric surgery is safe, with low reported perioperative mortality rates.

Weight loss surgery helps patients with severe obesity. This study looked at the risk of dying after weight loss surgery in over 3.6 million patients. The risk was less than 1 in 1000 (0.08 per cent). The risk was lowest for gastric band and sleeve gastrectomy, then for gastric bypasses and highest for the duodenal switch operation. This shows that weight loss surgery is safe, with a low risk of dying similar to that of other common operations.

Incidence and risk factors for esophageal cancer following achalasia treatment: national population-based case-control study.

The objective of this study is to identify the incidence of and risk factors associated with the development of esophageal cancer in treated achalasia patients in a national cohort. Patients with esophageal achalasia diagnosed and receiving a treatment between 2002 and 2012 were identified in England. Patient and treatment factors were compared between individuals who developed esophageal cancer and those that did not using univariate and multivariate analyses. A total of 7487 patients receiving an interventional treatment for esophageal achalasia were included and 101 patients (1.3%) developed esophageal cancer. The incidence of esophageal cancer was 205 cases per 100,000 patient years at risk. Patients who developed esophageal cancer were older and more commonly primarily treated with pneumatic dilation (82.2% vs. 60.3%; P < 0.001). In the esophageal cancer group, there was an increase in the number of patients requiring reinterventions (47.5% vs. 38.0%; P = 0.041) and the average total number of reinterventions per patient (1.2 vs. 0.8; P = 0.026). Multivariate analysis suggested associations between increased reintervention following both surgical myotomy (HR = 5.1; 95%CI 1.12-23.16) and pneumatic dilation (HR = 1.48; 95%CI 0.95-2.29), and esophageal cancer risk. Increasing patient age and reintervention following primary achalasia treatment are important potential risk factors for the development of esophageal cancer. Treated achalasia patients with symptom recurrence should be carefully evaluated for potential development of esophageal cancer prior to considering reintervention, and increased vigilance may help diagnose esophageal cancer in these individuals at an early stage.

Influence of national centralization of oesophagogastric cancer on management and clinical outcome from emergency upper gastrointestinal conditions.

BACKGROUND: In England in 2001 oesophagogastric cancer surgery was centralized. The aim of this study was to evaluate whether centralization of oesophagogastric cancer to high-volume centres has had an effect on mortality from different emergency upper gastrointestinal conditions. METHODS: The Hospital Episode Statistics database was used to identify patients admitted to hospitals in England (1997-2012). The influence of oesophagogastric high-volume cancer centre status (20 or more resections per year) on 30- and 90-day mortality from oesophageal perforation, paraoesophageal hernia and perforated peptic ulcer was analysed. RESULTS: Over the study interval, 3707, 12 441 and 56 822 patients with oesophageal perforation, paraoesophageal hernia and perforated peptic ulcer respectively were included. There was a passive centralization to high-volume cancer centres for oesophageal perforation (26·9 per cent increase), paraoesophageal hernia (19·5 per cent increase) and perforated peptic ulcer (23·0 per cent increase). Management of oesophageal perforation in high-volume centres was associated with a reduction in 30-day (HR 0·58, 95 per cent c.i. 0·45 to 0·74) and 90-day (HR 0·62, 0·49 to 0·77) mortality. High-volume cancer centre status did not affect mortality from paraoesophageal hernia or perforated peptic ulcer. Annual emergency admission volume thresholds at which mortality improved were observed for oesophageal perforation (5 patients) and paraoesophageal hernia (11). Following centralization, the proportion of patients managed in high-volume cancer centres that reached this volume threshold was 88·0 per cent for oesophageal perforation, but only 30·3 per cent for paraoesophageal hernia. CONCLUSION: Centralization of low incidence conditions such as oesophageal perforation to high-volume cancer centres provides a greater level of expertise and ultimately reduces mortality.

An observational study of the timing of surgery, use of laparoscopy and outcomes for acute cholecystitis in the USA and UK.

BACKGROUND: Evidence supports early laparoscopic cholecystectomy for acute cholecystitis. Differences in treatment patterns between the USA and UK, associated outcomes and resource utilization are not well understood. METHODS: In this retrospective, observational study using national administrative data, emergency patients admitted with acute cholecystitis were identified in England (Hospital Episode Statistics 1998-2012) and USA (National Inpatient Sample 1998-2011). Proportions of patients who underwent emergency cholecystectomy, utilization of laparoscopy and associated outcomes including length of stay (LOS) and complications were compared. The effect of delayed treatment on subsequent readmissions was evaluated for England. RESULTS: Patients with a diagnosis of acute cholecystitis totaled 1,191,331 in the USA vs. 288 907 in England. Emergency cholecystectomy was performed in 628,395 (52.7% USA) and 45,299 (15.7% England) over the time period. Laparoscopy was more common in the USA (82.8 vs. 37.9%; p < 0.001). Pre-treatment (1 vs. 2 days; p < 0.001) and total ( 4 vs. 7 days; p < 0.001) LOS was lower in the USA. Overall incidence of bile duct injury was higher in England than the USA (0.83 vs. 0.43%; p < 0.001), but was no different following laparoscopic surgery (0.1%). In England, 40.5% of patients without an immediate cholecystectomy were subsequently readmitted with cholecystitis. An additional 14.5% were admitted for other biliary complications, amounting to 2.7 readmissions per patient in the year following primary admission. CONCLUSION: This study highlights management practices for acute cholecystitis in the USA and England. Despite best evidence, index admission laparoscopic cholecystectomy is performed less in England, which significantly impacts subsequent healthcare utilization.

The influence of hospital volume upon clinical management and outcomes of esophageal achalasia: an English national population-based cohort study.

Management of achalasia is potentially complex. Previous studies have identified equivalence between pneumatic dilatation and surgical cardiomyotomy in terms of clinical outcomes. However, previous research has not investigated whether a management strategies and outcomes are different in high-volume achalasia centers. This national population-based cohort study aimed to identify the treatment modalities utilized in centers, which regularly manage achalasia and those which manage it infrequently. This study also assessed rates of re-intervention and complications to establish if a volume-outcome relationship exists for the management of achalasia in England. In this study, the Hospitals Episode Statistics database was used to identify all patients treated for achalasia in England from 2002 to 2012. Primary treatment was defined as surgical cardiomyotomy, sequential pneumatic dilatation, or botulinum toxin therapy. Primary outcome measure was reintervention. Centers were divided into regular achalasia centers (≥5.7 cases per annum) and infrequent achalasia centers (<5.7 cases per annum), and were analyzed according to tertiary cancer center status. In total, there were 7,487 patients treated for achalasia. Out of 1,947 cases (26%) were treated in regular achalasia centers, with 5,540 (74%) treated in infrequent centers. In binary logistic regression modeling regular centers treated a similar proportion of patients with primary surgical cardiomyotomy (OR: 1.11 (95% CI 0.98-1.27)) and had similar rates of re-intervention to infrequent achalasia centers (HR: 1.03 (0.94-1.12)). RA-CUSUM analysis demonstrated no relationship between total hospital volume and reintervention rates. Tertiary cancer centers treated more achalasia patients with primary surgical cardiomyotomy (OR: 1.51 (95% CI 1.31-1.73)) but there was no significant difference in reintervention rates (OR: 1.05 (95% CI 0.95-1.16)). In conclusion, this analysis failed to demonstrate a volume-outcome relationship in the management of achalasia in England. This study highlights that achalasia is treated infrequently by the majority of centers.

From the Knife to the Endoscope-a History of Bariatric Surgery.

PURPOSE OF REVIEW: Current bariatric surgical practice has developed from early procedures, some of which are no longer routinely performed. This review highlights how surgical practice in this area has developed over time. RECENT FINDINGS: This review outlines early procedures including jejuno-colic and jejuno-ileal bypass, initial experience with gastric bypass, vertical banded gastroplasty and biliopancreatic diversion with or without duodenal switch. The role laparoscopy has played in the widespread utilization of surgery for treatment of obesity will be described, as will the development of procedures which form the mainstay of current bariatric surgical practice including gastric bypass, sleeve gastrectomy and adjustable gastric banding. Endoscopic therapies for the treatment of obesity will be described. By outlining how bariatric surgical practice has developed over time, this review will help practicing surgeons understand how individual procedures have evolved and also provide insight into potential future developments in this field.

Benefits of barbed suture utilisation in gastrointestinal anastomosis: a systematic review and meta-analysis.

INTRODUCTION: Anastomosis formation constitutes a critical aspect of many gastrointestinal procedures. Barbed suture materials have been adopted by some surgeons to assist in this task. This systematic review and meta-analysis compares the safety and efficacy of barbed suture material for anastomosis formation compared with standard suture materials. METHODS: An electronic search of Embase, Medline, Web of Science and Cochrane databases was performed. Weighted mean differences were calculated for effect size of barbed suture material compared with standard material on continuous variables and pooled odds ratios were calculated for discrete variables. FINDINGS: There were nine studies included. Barbed suture material was associated with a significant reduction in overall operative time (WMD: -12.87 (95% CI = -20.16 to -5.58) (P = 0.0005)) and anastomosis time (WMD: -4.28 (95% CI = -6.80 to -1.75) (P = 0.0009)). There was no difference in rates of anastomotic leak (POR: 1.24 (95% CI = 0.89 to 1.71) (P = 0.19)), anastomotic bleeding (POR: 0.80 (95% CI = 0.29 to 2.16) (P = 0.41)), or anastomotic stricture (POR: 0.72 (95% CI = 0.21 to 2.41) (P = 0.59)). CONCLUSIONS: Use of barbed sutures for gastrointestinal anastomosis appears to be associated with shorter overall operative times. There was no difference in rates of complications (including anastomotic leak, bleeding or stricture) compared with standard suture materials.

Photoaffinity labelling of the beta-methoxyacrylate binding site in bovine heart mitochondrial cytochrome bc1 complex.

A carbene-generating 14C-labelled beta-methoxyacrylate derivative ((E)-methyl-3-methoxy-2-[4-(3-trifluoromethyl-3-diazirinyl) benzoyloxyphenyl] propanoate, uniformly labelled with 14C in the benzene ring of the benzoyl group) has been used to locate the proteins involved in binding this class of inhibitors to bovine heart mitochondrial ubihydroquinone:cytochrome c oxidoreductase. The beta-methoxyacrylate photoaffinity label was shown to be a competent inhibitor of electron transport through the protein complex. Under illumination through a narrow bandpass filter, allowing specific photolysis of the diazirine group, the compound bound to cytochrome b and weakly to an 8 kDa polypeptide. Apart from some binding to a cytochrome b aggregate, other proteins were left unlabelled. The binding could be prevented in the presence of excess amounts of unlabelled beta-methoxyacrylate, myxothiazol or stigmatellin but not by antimycin A or HQNO. At high concentrations DBMIB partially competed for the binding site. The binding site for this class of inhibitors is therefore the 'o-site'. Our results indicate that this site is comprised of residues from cytochrome b and possibly the 8 kDa polypeptide and that the site may be close to the Reiske iron-sulphur protein.

Differential susceptibility of primary cultured human skin cells to hypericin PDT in an in vitro model.

Skin cancer is the most common cancer worldwide, and its incidence rate in South Africa is increasing. Photodynamic therapy (PDT) has been shown to be an effective treatment modality, through topical administration, for treatment of non-melanoma skin cancers. Our group investigates hypericin-induced PDT (HYP-PDT) for the treatment of both non-melanoma and melanoma skin cancers. However, a prerequisite for effective cancer treatments is efficient and selective targeting of the tumoral cells with minimal collateral damage to the surrounding normal cells, as it is well established that cancer therapies have bystander effects on normal cells in the body, often causing undesirable side effects. The aim of this study was to investigate the cellular and molecular effects of HYP-PDT on normal primary human keratinocytes (Kc), melanocytes (Mc) and fibroblasts (Fb) in an in vitro tissue culture model which represented both the epidermal and dermal cellular compartments of human skin. Cell viability analysis revealed a differential cytotoxic response to a range of HYP-PDT doses in all the human skin cell types, showing that Fb (LD50=1.75µM) were the most susceptible to HYP-PDT, followed by Mc (LD50=3.5µM) and Kc (LD50>4µM HYP-PDT) These results correlated with the morphological analysis which displayed distinct morphological changes in Fb and Mc, 24h post treatment with non-lethal (1µM) and lethal (3µM) doses of HYP-PDT, but the highest HYP-PDT doses had no effect on Kc morphology. Fluorescent microscopy displayed cytoplasmic localization of HYP in all the 3 skin cell types and additionally, HYP was excluded from the nuclei in all the cell types. Intracellular ROS levels measured in Fb at 3µM HYP-PDT, displayed a significant 3.8 fold (p<0.05) increase in ROS, but no significant difference in ROS levels occurred in Mc or Kc. Furthermore, 64% (p<0.005) early apoptotic Fb and 20% (p<0.05) early apoptotic Mc were evident; using fluorescence activated cell sorting (FACS), 24h post 3µM HYP-PDT. These results depict a differential response to HYP-PDT by different human skin cells thus highlighting the efficacy and indeed, the potential bystander effect of if administered in vivo. This study contributes toward our knowledge of the cellular response of the epidermis to photodynamic therapies and will possibly enhance the efficacy of future photobiological treatments.

Anastomotic reinforcement with omentoplasty following gastrointestinal anastomosis: A systematic review and meta-analysis.

Anastomotic leak is a potentially devastating complication following gastrointestinal anastomosis. Some surgeons believe that reinforcing the anastomosis with omentum reduces the incidence and severity of anastomotic leak. A comprehensive electronic search of EMBASE, Medline, Web of Science and Cochrane databases was performed. Pooled odds ratios (POR) were calculated for discrete variables. There were six studies investigating esophageal anastomosis and 3 studies investigating colorectal anastomosis identified by the literature search. A total of 2296 patients were included, 1073 with omentoplasty and 1223 without. In esophageal surgery omentoplasty significantly reduced the rate of anastomotic leak (2.9% vs 10.5% (POR = 0.28; 95% CI = 0.17 to 0.47; P < 0.0001), but there was no significant effect upon in-hospital mortality (2.3% vs. 2.5%; POR = 0.911 [95% CI 0.439-1.887]; P = 0.802) or anastomotic stricture between the two groups (6.6% vs 9.1%; POR = 0.842 [95% CI 0.331 to 2.145]; P = 0.720). In colorectal surgery there was no significant difference in anastomotic leak rate (5.0% vs 8.4%; POR: 0.50; 95% CI 0.21 to 1.17) or in-hospital mortality (4.2% vs 4.1%; POR: 0.90; 95% CI 0.34 to 2.41). The results of this analysis show that omentoplasty significantly reduced the rate of anastomotic leak following esophageal anastomosis but these results were not observed in colorectal anastomosis. Omentoplasty could be used as an adjunct technique to reduce the incidence of anastomotic leak in oesophageal anastomosis.

Superior fatigue resistance of elite black South African distance runners.

Black athletes currently dominate long-distance running events in South Africa. In an attempt to explain an apparently superior running ability of black South African athletes at distances > 3 km, we compared physiological measurements in the fastest 9 white and 11 black South African middle-to long-distance runners. Whereas both groups ran at a similar percentage of maximal O2 uptake (%VO2max) over 1.65-5 km, the %VO2max sustained by black athletes was greater than that of white athletes at distances > 5 km (P < 0.001). Although both groups had similar training volumes, black athletes reported that they completed more exercise at > 80% VO2max (36 +/- 18 vs. 14 +/- 7%: P < 0.005). When corrections were made for the black athletes' smaller body mass, their superior ability to sustain a high %VO2max could not be explained by any differences in VO2max, maximal ventilation, or submaximal running economy. Superior distance running performance of the black athletes was not due to a greater (+/- 50%) percentage of type I fibers but was associated with lower blood lactate concentrations during exercise. Time to fatigue during repetitive isometric muscle contractions was also longer in black runners (169 +/- 65 vs. 97 +/- 69 s; P < 0.05), but whether this observation explains the superior endurance or was due to the lower peak muscle strength (46.3 +/- 10.3 vs. 67.5 +/- 18.0 Nm/l lean thigh volume; P < 0.01) remains to be established.

Increased noradrenergic activity in prefrontal cortex slices of an animal model for attention-deficit hyperactivity disorder--the spontaneously hypertensive rat.

Spontaneously hypertensive rats (SHR) are used as a model for attention-deficit/hyperactivity disorder (ADHD) since SHR are hyperactive and they show defective sustained attention in behavioral tasks. Using an in vitro superfusion technique we showed that norepinephrine (NE) release from prefrontal cortex slices of SHR was not different from that of their Wistar-Kyoto (WKY) control rats when stimulated either electrically or by exposure to buffer containing 25 mM K(+). The monoamine vesicle transporter is, therefore, unlikely to be responsible for the deficiency in DA observed in SHR, since, in contrast to DA, vesicle stores of NE do not appear to be depleted in SHR. In addition, alpha(2)-adrenoceptor mediated inhibition of NE release was reduced in SHR, suggesting that autoreceptor function was deficient in prefrontal cortex of SHR. So, while DA neurotransmission appears to be down-regulated in SHR, the NE system appears to be under less inhibitory control than in WKY suggesting hypodopaminergic and hypernoradrenergic activity in prefrontal cortex of SHR. These findings are consistent with the hypothesis that the behavioral disturbances of ADHD are the result of an imbalance between NE and DA systems in the prefrontal cortex, with inhibitory DA activity being decreased and NE activity increased relative to controls.

A clinical outcome and cost analysis of laparoscopic versus open appendectomy.

BACKGROUND: Benefits of laparoscopic appendectomy are controversial, and the results of recent clinical studies have contradictory conclusions. We performed a cost analysis comparing laparoscopic and open appendectomies to assess potential efficacy of the laparoscopic approach. METHODS: All patients operated on for suspected acute appendicitis at the University of Washington Medical Center (UWMC) from January 1, 1991 through January 1, 1995 were analyzed. Potential benefits of the laparoscopic approach were examined in five major categories: hospital length of stay, total hospital charges, operative time, operating room charges, and postoperative complications. Patients were stratified according to the presence or absence of perforation for outcome analysis. RESULTS: There were 163 appendectomies performed in 82 men and 81 women. Twenty-seven (17%) patients had laparoscopic evaluation, of which 21 underwent attempted laparoscopic appendectomy. Among nonperforated patients, laparoscopic appendectomy did not reduce hospital stay compared with open appendectomy, but did lead to greater hospital charges ($7760 vs $5064; P < 0.001). Operating times were longer in the laparoscopic group (104 vs 74 minutes; P < 0.001) compared with open appendectomies. Operating room charges for laparoscopic appendectomies exceeded charges for the open approach ($4740 vs $1870; P < 0.001). Complication rates were similar (laparoscopic, 19% vs open, 16%; NS). The false diagnostic rate for women was four times greater than for men among patients undergoing open appendectomy (31% vs 8%; P < 0.01). Patients with perforation undergoing a midline incision had a longer hospital stay (9.5 vs 5.9; P < 0.02) than patients operated on through a right lower quadrant incision. CONCLUSIONS: In our analysis, laparoscopic appendectomy, while safe, was more expensive and was not associated with better clinical outcome compared with open appendectomy patients.

Use of the surgical Apgar score to guide postoperative care.

INTRODUCTION: The surgical Apgar score (SAS) can predict 30-day major complications or death after surgery. Studies have validated the score in different patient populations and suggest it should be used to objectively guide postoperative care. We aimed to see whether using the SAS in a decisive approach in a future randomised controlled trial (RCT) would be likely to demonstrate an effect on postoperative care and clinical outcome. METHODS: A total of 143 adults undergoing general/vascular surgery in 9 National Health Service hospitals were recruited to a pilot single blinded RCT and the data for 139 of these were analysed. Participants were randomised to a control group with standard postoperative care or to an intervention group with care influenced (but not mandated) by the SAS (decisive approach). The notional primary outcome was 30-day major complications or death. RESULTS: Incidence of major complications was similar in both groups (control: 20/69 [29%], intervention: 23/70 [33%], p=0.622). Immediate admissions to the critical care unit was higher in the intervention group, especially in the SAS 0-4 subgroup (4/6 vs 2/7) although this was not statistically significant (p=0.310). Validity was also confirmed in area under the curve (AUC) analysis (AUC: 0.77). CONCLUSIONS: This pilot study found that a future RCT to investigate the effect of using the SAS in a decisive approach may demonstrate a difference in postoperative care. However, significant changes to the design are needed if differences in clinical outcome are to be achieved reliably. These would include a wider array of postoperative interventions implemented using a quality improvement approach in a stepped wedge cluster design with blinded collection of outcome data.

Reflectivity changes of Ge and the efficiency of moving diffraction gratings.

Reflectivity changes and the efficiency of a temporary grating formed on a Ge surface by two beams, which differ in frequency by 26 MHz, are compared with those measured for beams of equal frequency. The results indicate that the observations can be explained by a deterioration in the quality of the grating due to its motion across the surface. The predicted effects due to a phase difference between the intensity pattern and the temperature variation on the surface which it produces were not observed.

Compact recording of the appearance of surfaces and thin films.

For improvement of optical surfaces and reflectivity enhancing films and for comparison with their appearance after use or testing, it is necessary to observe and record the nature of a surface or film with high resolution. Modifications of standard Twyman-Green and knife-edge testing methods are presented which meet this need. The appearance of flat surfaces of 40-mm diam can be preserved on a single photographic emulsion. Examples showing film defects due to reflectivity or phase changes with resolution of a few microns are presented.

Increased glutamate-stimulated norepinephrine release from prefrontal cortex slices of spontaneously hypertensive rats.

Spontaneously hypertensive rats (SHR) have behavioral characteristics (hyperactivity, impulsiveness, poorly sustained attention) similar to the behavioral disturbances of children with attention-deficit hyperactivity disorder (ADHD). We have previously shown that dopaminergic and noradrenergic systems are disturbed in the prefrontal cortex of SHR compared to their normotensive Wistar-Kyoto (WKY) control rats. It was of interest to determine whether the underlying neural circuits that use glutamate as a neurotransmitter function normally in the prefrontal cortex of SHR. An in vitro superfusion technique was used to demonstrate that glutamate caused a concentration-dependent stimulation of [3H]norepinephrine release from rat prefrontal cortex slices. Glutamate (100 microM and 1 mM) caused significantly greater release of norepinephrine from prefrontal cortex slices of SHR than from control slices. The effect of glutamate was not mediated by NMDA receptors, since NMDA (10 and 100 microM) did not exert any effect on norepinephrine release and MK-801 (10 microM) did not antagonize the effect of 100 microM glutamate. These results demonstrate that glutamate stimulates norepinephrine release from rat prefrontal cortex slices and that this increase is enhanced in SHR. The results are consistent with the suggestion that the noradrenergic system is overactive in prefrontal cortex of SHR, the animal model for ADHD.

High-efficiency diffractionless beams of constant size and intensity.

Design considerations are presented for pairs of spherically aberrating elements that produce diffractionless beams of high efficiency and nearly constant size and intensity over specified ranges of axial position. An approximate design, assuming an aberration quadratic in radial ray positions, is followed by a final lens (mirror) specification that is verified through meridional ray tracing. This then provides an accurate determination of beam characteristics. Examples are presented that represent a variety of applications. As a design aid, a simple prescription is given for generating families of substantially different Bessel-like beams from any given pair of elements under small changes in element separation. Pattern sizes and ranges are compared with those of Gaussian beams, shadow lengths are examined for Bessel-type beams, and beam efficiencies are fully analyzed.

Observation and morphology of small-scale laser induced damage.

Laser-induced damage of lambda/4 ThF(4)/ZnS coatings for 10.6 microm is studied. Extended areas of the coated surfaces are recorded on high resolution film both before and after irradiation using Twyman-Green and knife-edge techniques, the latter method proving to be superior and quite useful. Comparisons are made to establish a possible correlation between the location of damage sites and previous defects. The morphology of the damage is also studied using Nomarski microscopy to determine possible causes of damage. Damage on coated silicon substrates resembles melts and burns with cracking and/or annealing around some burned areas, while damage to the coated silica substrates resembles bubbles that are arranged along scratches or in clusters. The high correlation between damage sites and previous defects suggests that clean defect-free coatings have greatly increased damage thresholds.