Passive stabilization of a synchronously mode-locked NaCl color-center laser by coherent photon seeding.

We use coherent photon seeding to passively stabilize a synchronously mode-locked NaCl color-center laser. This results in the generation of essentially transform-limited picosecond pulses with average power levels of as high as 1.3 W in the 1.5-1.7-microm range. In addition, the pulse energy fluctuations are reduced by as much as 1 order of magnitude.

Optical and laser properties of (F(2)(+))(H) centers in sulfur-doped NaCl.

We report the production and main optical and laser properties of (F(2)(+))(H) color centers in sulfur-doped NaCl crystals. Using a 1.06-microm Nd:YAG laser as the pump source, we realize continuous-wave and synchronously mode-locked laser operation. The laser is tunable over a remarkably large wavelength range of 1.43-2.0 microm. Output power levels are as much as ~800 mW near 1.6 microm; mode-locked pulse durations are typically 4-7 ps.

Subpicosecond and continuous-wave laser operation of (F(2)(+))(H) and (F(2)(+))(AH) color-center lasers in the 2-microm range.

We report synchronously mode-locked subpicosecond and continuous-wave color-center laser operation in the 1.8-2.4-microm wavelength range. For active materials we use (F(2)(+))(H) centers in KBr:O(2)(-) and (F(2)(+))(AH) centers in KBr:Na(+):O(2)(-) crystals. When the lasers are pumped with a continuous-wave or mode-locked NaCI (F(2)(+))(H)-center laser in a cascaded configuration, laser operation is obtained over the combined tuning range of 1.8-2.4 microm, with output powers as high as 150 mW. When synchronously mode locked with ~5-ps pump pulses, both KBr lasers yield typically ~1-ps pulse widths over the entire tuning range. Pulses as short as ~400 fs could be obtained at the expense of higher noise levels.

Femtosecond pulses with high energies from a coupled-cavity saturable-absorber mode-locked KCl F(A)(Tl) color-center laser.

By using a bulk InGaAsP saturable absorber, we passively mode lock a KCl F(A)(Tl) color-center laser in a resonator configuration where the gain material is placed in a main cavity and the saturable absorber is placed in a weakly coupled external cavity. We obtain self-starting and self-stabilized resonant passive mode-locked laser operation, either with pulses as short as ~320 fs or average output power as high as ~380 mW. The pulse width-bandwidth product is ~0.47, with pulse energies of as much as 2.5 nJ. By temperature tuning the saturable absorber band edge, we realize laser operation with similar performance over the wavelength range of 1.50-1.55 microm. When compared with mode-locked KCl F(A)(Tl) laser operation, where both the gain material and the saturable absorber are placed in a common single cavity, the resonant passive mode-locking technique yields pulses with only moderately increased widths (by ~50 fs) but significantly higher energies (by a factor of ~4).

Accuracy of radiologic and endoscopic diagnosis of duodenal ulcer.

On the basis of results of barium examination and upper gastrointestinal endoscopy four diagnostic criteria of duodenal ulcer can be formed: 1) radiography reveals an ulcer, 2) endoscopy reveals an ulcer, 3) both radiography and endoscopy reveal an ulcer, and 4) radiography and/or endoscopy reveals an ulcer. In a consecutive series of 156 patients the accuracy of each of the four diagnostic criteria was determined using the findings of an experienced specialist in upper gastrointestinal endoscopy as a reference. The predictive value of a positive diagnosis (PVpos) for the four diagnostic criteria was 0.63, 0.88, 1, and 0.68, respectively, and the predictive value of a negative diagnosis (PVneg) for all four criteria was around 0.90. The selection of diagnostic criteria should therefore depend on the clinical problem.

Accuracy of radiologic and endoscopic diagnosis of gastric ulcer.

Patients with upper abdominal pain are often examined with both double contrast study of the stomach and endoscopy. On the basis of the results of the two examinations four diagnostic criteria of an ulcer can be formed: 1) radiography reveals an ulcer, 2) endoscopy reveals an ulcer, 3) both radiography and endoscopy reveal an ulcer, and 4) radiography and/or endoscopy reveals an ulcer. In a prospective study the accuracy of each of the four diagnostic criteria was examined. Eighty-two randomly selected outpatients had a double contrast barium examination and an upper gastrointestinal endoscopy performed by staff personnel. The diagnosis of a specialist in upper gastrointestinal endoscopy was used as the standard. For the four diagnostic criteria the overall accuracy ranged from 0.80 to 0.88. The predictive value of a positive test result was around 0.70 and the predictive value of a negative test result ranged from 0.81 to 0.96. The specificity ranged from 0.87 to 0.95, and the sensitivity from 0.38 to 0.90. It is concluded that from a clinical point of view, the accuracy of the four diagnostic criteria does not differ to an extent that justifies recommendation of one diagnostic criterion of gastric ulcer rather than the other.

The endoscopic diagnosis of duodenal ulcer disease. A randomized clinical trial of bias and of interobserver variation.

In a randomized design we examined whether endoscopists are biased by knowledge of the radiologic diagnosis of duodenal ulcer and deformity of the duodenal bulb when recording the corresponding endoscopic diagnoses. A total of 156 patients had a barium meal and were subsequently randomized into 2 groups. In 74 of the cases the 2 endoscopists knew the result of the X-ray examination when doing the endoscopy; in 82 of the cases they did not. One endoscopist was significantly biased by his knowledge of the radiologic diagnosis of deformity of the duodenal bulb. Neither of the endoscopists was biased by his knowledge of the radiologic diagnosis of duodenal ulcer. In addition, the interobserver variation between the two endoscopists with regard to the endoscopic diagnoses of duodenal ulcer, deformity of the duodenal bulb, and duodenitis was examined. The interobserver variation was expressed by the overall agreement and by the kappa statistics, which adjusts the overall agreement for expected chance agreement. For duodenal ulcer, deformity of the duodenal bulb, and duodenitis, the overall agreements and kappa values were 0.91, 0.78, and 0.75, and 0.54, 0.42, and 0.33, respectively.

The endoscopic diagnosis of gastric ulcer. A randomized clinical trial of interobserver variation and bias induced by knowledge of the radiological diagnosis.

A critical evaluation of the endoscopic diagnosis of gastric ulcer was carried out. In a randomized design it was elucidated whether endoscopists are biased by knowledge of the radiological diagnosis when interpreting their endoscopic findings. In addition, the interobserver variation of the endoscopic diagnosis was determined. A total of 156 patients had a barium-meal examination and were subsequently endoscoped by the same two physicians in one session. Before the endoscopy, the patients were randomized in two groups. In 74 patients the physicians knew the radiologic result at the endoscopy; in 82 they did not. One endoscopist was significantly influenced by his knowledge of the radiological diagnosis. The interobserver variation, expressed as the kappa coefficient, was 0.54 and 0.60, respectively, in the two groups. The disagreement especially concerned small ulcers.

Cooperation between hospital and general practice in multipractice studies. Personal experiences from a study on early diagnosis for gastric cancer.

In this study close cooperation between general practice and out patient clinic made it possible to establish earlier diagnosis of serious disease using advanced diagnostic methods on patients seen only in general practice. However, the cooperation established in an attempt to diagnose gastric cancer at an early stage using endoscopic technique revealed major practical problems. It was difficult to make exact calculations of the background population because of the degree of the patients' right to choose a general practitioner. Furthermore, referral of all patients wanted for investigation proved a major obstacle, because of differences in workload and lack of understanding of scientific principles among the participating general practitioners. The desired cooperation between general practice and out patient clinics cannot easily be established in a way which gives us exact and scientifically reliable data, and such cooperation-for scientific purposes--can only involve smaller groups of doctors. However, the education of general practitioners in scientific methods and understanding, and hospital doctors in knowledge about the consequences of working conditions in general practice should be considerably improved.

Association between duodenal bulb ulceration and reduced exocrine pancreatic function.

Seventy two patients admitted to a medical department with dyspepsia but without a previous diagnosis of peptic ulcer disease or chronic pancreatitis were studied consecutively. A pancreatic function test (Lundh meal test) and an upper endoscopy was made in all patients. There was no difference in age, sex ratio, occurrence of upper abdominal pain or chronic alcoholism between the groups of patients with reduced pancreatic function (20) and the group with normal function (52). Seven duodenal ulcers were found, two in patients with normal pancreatic function (2/52 = 3.8%; 95% conf lim: 0.5-13.2) and five in patients with reduced pancreatic function (5/20 = 25%; 95% conf lim: 8.7-49.1). This difference was statistically significant (p less than 0.01). Duodenitis occurred with equal frequency in the two groups.

Prophylactic effect of cimetidine in gastric ulcer patients.

Nineteen patients entered a double-blind randomized trial of the prophylactic effect of cimetidine in gastric ulcer disease. The diagnosis of gastric ulcer had been established endoscopically prior to the trial, but at the time of entry the patients were symptom-free and their ulcers had healed. The patients received either cimetidine, 400 mg twice daily or inactive tablets. Ten cimetidine-treated patients completed 12 months' treatment without suffering a recurrence of symptoms, whereas 5 of 9 placebo-treated patients suffered a symptomatic relapse after 7 to 18 weeks (P less than 0.025). In 4 of the 5 patients an ulcer was found at gastroscopy. It is concluded that maintenance treatment with cimetidine helps to prevent symptomatic relapses in gastric ulcer patients.