PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Lasers, Solid-State”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2Linked to original sources

Holmium:YAG laser thermokeratoplasty for hyperopia.

Holmium:YAG laser thermokeratoplasty (LTK), a procedure using a solid-state infrared laser to treat hyperopia, was performed on 10 patients in phase I and 16 patients in phase II--in a total of 29 eyes at the Hunkeler Eye Clinic. Phase II was redesigned after phase I results showed undercorrection and regression. The follow-up period ranged from 1 to 24 months (mean 10.9 months). A total of 79% of phase II patients were within +/- 1.00 D of intended correction at the 6-month visit. Looking at both phases together, no patients had J2 or better near vision preoperatively, but 75% had J2 or better at the 6-month visit. A total of 43% of eyes in phase II lost 1 line and 7% lost two lines of best spectacle corrected visual acuity due to induction of irregular astigmatism. The surgical challenges are to insure appropriate centration of the procedure about the optical axis. Concerns about regression and stability will be defined as these patients are followed through their 2-year visits.

Cornea↗

Efficacy and safety of thulium fiber laser versus conventional holmium:YAG laser in anatomical endoscopic enucleation of the prostate: a systematic review and pairwise meta-analysis.

PURPOSE: Anatomical endoscopic enucleation is an established treatment for benign prostatic obstruction. Whether thulium fiber laser enucleation (ThuFLEP) improves outcomes over conventional holmium:YAG laser enucleation (HoLEP) remains uncertain. We compared the efficacy and safety of ThuFLEP versus non-MOSES-modulated HoLEP. METHODS: We performed a PRISMA-compliant systematic review and pairwise meta-analysis of randomised and comparative cohort studies comparing ThuFLEP and conventional HoLEP in adult men. Six databases were searched. Outcomes included International Prostate Symptom Score (IPSS), IPSS quality-of-life score, maximum urinary flow rate (Qmax), post-void residual volume, hospital stay, and complications. Risk of bias and certainty of evidence were assessed with RoB 2/ROBINS-I and GRADE. RESULTS: Seven non-overlapping comparative populations in eight publications included 3,509 patients. ThuFLEP was associated with a small statistically significant reduction in IPSS at 3 months (mean difference [MD] -1.04 points, 95% confidence interval [CI] -1.81 to -0.28) of uncertain clinical relevance. Qmax differences were small and directionally inconsistent across follow-up (favouring HoLEP at 3 months and ThuFLEP at 6 and 12 months) and derived mainly from retrospective cohorts, with neutral randomised subgroups. Stress and urge urinary incontinence were less frequent overall (RR 0.75, 95% CI 0.58 to 0.96, and RR 0.39, 95% CI 0.22 to 0.68), but both estimates depended on one large registry cohort and were not robust to its exclusion. Most other complications and hospital stay showed no clear between-group difference. Limitations include few studies per outcome, heterogeneity, sparse safety events, inconsistent prostate-specific antigen reporting, and mostly low/very low certainty evidence. CONCLUSION: ThuFLEP and conventional HoLEP are clinically comparable with no definitive superiority of either laser. Platform selection should be individualised according to surgeon expertise, institutional resources, and patient characteristics. Future trials should standardise cost-effectiveness outcomes and investigate whether the distinct laser-tissue interactions impact adenoma clearance, PSA reduction, enucleation completeness, and long-term durability.

Humans↗

Effectiveness of high-power laser use in the removal of esthetic restorations: a systematic review.

This systematic review aimed to evaluate the effectiveness of high-power lasers in the removal of esthetic restorations compared with conventional methods. The review was conducted in accordance with the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) and registered in PROSPERO (registration number: CRD420251055736). A comprehensive electronic search was performed in MEDLINE, Scopus, Embase, Web of Science, and the Cochrane Library. Study selection, data extraction, and methodological quality assessment were independently performed by four reviewers using QUIN tool for in vitro studies. A total of 2.384 records were identified, of which 19 in vitro studies conducted on extracted human permanent teeth met the eligibility criteria and were included in the qualitative synthesis. The included studies evaluated different high-power laser systems, predominantly Er: YAG and Er, Cr: YSGG lasers, as well as CO₂ lasers. Five studies were classified as high quality, whereas the remaining fourteen studies were classified as moderate quality. Available laboratory evidence suggests that laser-assisted techniques may represent a potential alternative approach for removing esthetic restorations, with advantages including conservative tissue removal, reduced damage to underlying tooth structures, and intrapulpal temperature increases within acceptable limits. The Er: YAG laser was the most frequently investigated system, with power settings ranging from 1.5 to 5.9 W, showing particularly favorable laboratorial performance in the removal of lithium disilicate restorations, especially in thinner substrates. Within the limitations of the available evidence, high-power lasers appear to be a promising and minimally invasive alternative to conventional methods for the removal of esthetic restorations. However, the predominance of in vitro studies highlights the need for well-designed clinical trials to confirm these findings and support their clinical application.

Humans↗

Holmium laser enucleation of the prostate for the treatment of lower urinary tract symptoms in men with benign prostatic hyperplasia.

RATIONALE: A range of surgical options is available for the treatment of benign prostatic hyperplasia (BPH), including holmium laser enucleation of the prostate (HoLEP). The evidence is unclear regarding differences in functional, perioperative, and morbidity outcomes between these modalities. OBJECTIVES: To assess the effects of holmium laser enucleation of the prostate compared with other surgical treatments for lower urinary tract symptoms in men with benign prostatic hyperplasia. SEARCH METHODS: We searched multiple databases (including MEDLINE, Embase, CENTRAL, Web of Science, LILACS, and the International HTA database), trial registries, and conference abstracts through April 08, 2026. ELIGIBILITY CRITERIA: We only included randomized trials of men over 40 years of age with a prostate volume of at least 20 mL (assessed by digital rectal examination, ultrasound, or conventional imaging) who exhibited lower urinary tract symptoms (LUTS) defined by an International Prostate Symptom Score (IPSS) of eight or greater undergoing surgical interventions for BPH. OUTCOMES: The critical outcomes measured were the urologic symptoms score, the quality-of-life score, and major adverse events. The important outcomes measured were: re-treatment, erectile function, ejaculatory function, transfusions, acute urinary retention, indwelling urinary catheter duration, and hospital stay duration. RISK OF BIAS: We used the Cochrane risk of bias tool (RoB 1) to assess for potential sources of bias on a study and outcome level basis. SYNTHESIS METHODS: We pooled outcome data using the random-effects model and performed meta-analyses using the Mantel-Haenszel method. We assessed statistical heterogeneity in the pooled data by visually inspecting forest plots and using the I2 statistic to quantify it. We used the GRADE framework to assess the certainty of evidence. INCLUDED STUDIES: We included 52 trials that included 6242 participants that compared HoLEP to other surgical interventions for benign prostatic hyperplasia. The median age of participants across the studies ranged from 65 to 74 years. The baseline prostate volume ranged from 30 cc to 142 cc. Baseline IPSS scores ranged from 19.6 to 28.6 (range 0-35). SYNTHESIS OF RESULTS: We prioritized comparing HoLEP with transurethral resection of the prostate (TURP) at short-term follow-up (up to 12 months), because TURP is the long-standing reference standard and the predominant comparator in randomized surgical trials. Findings for the four remaining comparisons (laser ablation, alternative energy source enucleation, other minimally invasive therapies, and simple prostatectomy), for long-term follow-up, and for all remaining outcomes are reported in full in the review. Compared to TURP, at short-term follow-up: Critical outcomes - HoLEP may result in little to no difference in short-term urologic symptom scores measured using the IPSS (range 0 to 35; lower values reflect fewer symptoms) (MD -0.67, 95% CI -1.20 to -0.14; I² = 93%; 14 studies, 1666 participants, low-certainty evidence). - HoLEP may result in little to no difference in short-term quality of life (range 0 to 6; lower values reflect better quality of life) (MD -0.04, 95% CI -0.23 to 0.15; I² = 73%; 6 studies, 876 participants, low-certainty evidence). - HoLEP may result in little to no difference in short-term major adverse events (RR 0.75, 95% CI 0.35 to 1.58; I² = 0%; 10 studies, 1147 participants, low-certainty evidence). Important outcomes - HoLEP likely results in little to no difference in re-treatment (RR 0.45, 95% CI 0.14 to 1.50; I² = 0%; 8 studies, 813 participants, moderate-certainty evidence). - HoLEP likely results in little to no difference in erectile function (MD -0.03, 95% CI -0.47 to 0.42; I² = 0%; 3 studies, 518 participants, moderate-certainty evidence). - Ejaculatory function: we did not find any data for this outcome. - HoLEP likely reduces the need for blood transfusion (RR 0.19, 95% CI 0.09 to 0.42; I² = 0%; 15 studies, 1755 participants, moderate-certainty evidence). AUTHORS' CONCLUSIONS: Compared with TURP, HoLEP may achieve similar relief of urologic symptoms, similar quality of life, and similar rates of major adverse events in the first 12 months after surgery, and probably similar re-treatment rates and erectile function. HoLEP likely reduces the need for blood transfusion; this is the only advantage of HoLEP that the randomized evidence, as summarized here, supports as clinically important. There was insufficient evidence to assess outcomes in the subset of individuals with larger prostates or on anticoagulation. Future research should prioritize long-term trials reporting sexual function and urinary incontinence outcomes, recruit men with very large prostates (≥ 150 cc) or on anticoagulation therapy, and evaluate cost-effectiveness and training requirements. FUNDING: No external funding was received for this review. REGISTRATION: The protocol for this review was published in the Cochrane Database 2019 (https://doi.org/10.1002/14651858.CD013291).

Humans↗

[Holmium:YAG and erbium:YAG infrared laser osteotomy].

The in-vivo bone ablation characteristics of a pulsed solid-state erbium:YAG laser were compared to those of a pulsed solid-state holmium:YAG laser. Partial osteotomies in the maxillary, the mandibulary, and the nasal bones of white rats were performed. The tissue response was examined by light microscopy. Thermal gradients following the laser application were also measured. Over all energy levels tested the erbium:YAG laser produced ablation of bone with minimal thermal damage to the adjacent tissue. The results of this study are promising for future application of the infrared holmium- and erbium:YAG lasers in otorhinolaryngology.

Animals↗

Comparison of a 755-nm picosecond laser and a 1565-nm nonablative fractional laser for the treatment of atrophic acne scars: a 20-week prospective, randomized, split-face clinical study.

To compare the efficacy and safety of a 755-nm picosecond laser with a diffractive lens array (P-DLA) and a 1565-nm nonablative fractional laser (NAFL) for the treatment of atrophic acne scars. Twenty-seven patients with atrophic acne scars underwent three sessions of randomized split-face treatment with P-DLA and NAFL at 4-week intervals. Patients were followed up at 1, 2, and 3 months after the final treatment. Efficacy was assessed using the &#xc9;chelle d'&#xc9;valuation Clinique des Cicatrices d'Acn&#xe9; (ECCA) grading scale, the Investigator's Global Assessment (IGA) score, patients' self-rated improvement, and overall satisfaction. Treatment-related adverse reactions were recorded daily by patients until resolution. Both modalities demonstrated significant improvements in scar appearance based on ECCA score, IGA score, and patients' self-rated improvement (P&#x2009;<&#x2009;0.001). No statistically significant differences in efficacy were observed between the two treatments. However, the P-DLA group showed higher patient satisfaction (P&#x2009;=&#x2009;0.035) and a more favorable safety profile, including shorter durations of erythema and edema and the absence of crusting. Both P-DLA and NAFL were effective and safe for the treatment of atrophic acne scars, with similar efficacy. P-DLA offered better tolerability.

Humans↗

Characterization of protease-catalyzed hydrolysis of cyanine-labeled angiotensin using capillary electrophoresis with laser-induced fluorescence detection.

The hydrolytic cleavage of a cyanine (Cy3)-labeled angiotensin, catalyzed by various proteases, was studied by capillary electrophoresis (CE) with laser-induced fluorescence detection (LIF). The end-labeled peptides and the Cy3 diacid internal standard were separated on a 20-microns x 27-cm capillary with LIF detection (emission, 580 nm) using a frequency-doubled solid-state diode laser emitting at 532 nm or a He-Ne laser emitting at 543 nm. Hydrolysis of the Cy3-labeled angiotensin I, catalyzed by proteinase K, is a sequential process beginning from the C-terminal of the peptide, instead of from random cleavages. Trypsin catalyzes a specific cleavage of Cy3-angiotensin I to Cy3-Asp-Arg as anticipated. Using a combination of endopeptidase and carboxypeptidases, the remnant of the labeled species was characterized by CE-LIF. The method provides a general tool for studying the mechanism of protease-catalyzed hydrolysis of peptide.

Amino Acid Sequence↗

Minimal access surgery and the future of interventional laparoscopy.

Minimal access surgery is intended to minimize the trauma of access without compromising exposure of the operative field. Its major benefits include diminished cost of therapy due to a reduced hospital stay and accelerated recovery with early return to full activity. The approaches used in minimal access surgery are laparoscopic, endoluminal, perivisceral, intra-articular, and combined. Many abdominal and thoracic procedures are being adapted to the minimal access approach. Developmental requirements include improvements in light delivery systems; three-dimensional television imaging; better surgical instrumentation; ultrasound probes for internal and external scanning; stapling devices; and tunable, portable solid-state diode lasers. In addition, however, adequate prospective evaluation of laparoscopic procedures, established or new, must be undertaken in the major academic institutions.

Evaluation Studies as Topic↗

Transient tension changes initiated by laser temperature jumps in rabbit psoas muscle fibres.

1. A technique was developed to generate 2-8 degrees C step temperature perturbations (T-jumps) in single muscle fibres to study the thermodynamics of muscle contraction. A solid-state pulsed holmium laser emitting at 2.065 microns heated the fibre and surrounding solution in approximately 150 mus. The signal from a 100 microns thermocouple fed back to a heating wire maintained the elevated temperature after the laser pulse. 2. Tension of glycerol-extracted muscle fibres from rabbit psoas muscle did not change significantly following T-jumps when the fibre was relaxed. 3. In rigor, tension decreased abruptly on heating indicating normal (not rubber-like) thermoelasticity. The thermoelastic coefficient (negative ratio of relative length change to relative temperature change) of the fibre was estimated to be -0.021 at sarcomere lengths of 2.5-2.8 microns. Rigor tension was constant after the temperature step and returned to the original value on recooling. 4. In maximal Ca2+ activation, tension transients initiated by T-jumps had several phases. An immediate tension decrease suggests that thermoelasticity during contraction is similar to that in rigor. Active tension then recovered to the value before the T-jump with an apparent rate constant of approximately 400 s-1 (at 10-20 degrees C). This rate constant did not have an appreciable dependence on the final temperature. Finally, tension increased exponentially to a new higher level with a rate constant of approximately 20 s-1 at 20 degrees C. This rate constant increased with temperature with a Q10 of 1.4. 5. At submaximal Ca2+ activation the tension rise was followed by a decay to below the value before the T-jump. This decline was expected from the temperature dependence of steady pCa-tension curves. The final tension decline occurred on the 1-5 s time scale. 6. The value and amplitude dependence of the rate constant for the quick recovery following T-jumps were similar to those of the quick recovery following length steps during active contractions. The enthalpy change associated with the quick tension recovery following temperature-step perturbations was estimated to be positive suggesting that the recovery process is an endothermic reaction. Slower reaction steps on the 10-30 ms timescale, as well as reactions corresponding to the quick recovery, may contribute to the cross-bridge power stroke.

Animals↗

Rapid quantitative analysis of differential PCR products by high-performance liquid chromatography.

We describe the use of high-performance liquid chromatography (HPLC) for the rapid quantitative analysis of short DNA fragments generated in differential PCR, where a target gene and a control gene are in vitro coamplified in one single reaction. Using an anion-exchange nonporous column, both separation and quantitation of the differential PCR products are achieved in about 5 min per sample. The performance of this technique proved to be superior to that of conventional gel electrophoresis and subsequent analysis by a laser densitometer, a solid-state scanner and a charge coupled device video camera imaging system. The usefulness for clinical testing is described in the example of the quantitative analysis of the c-erbB-2 oncogene copy number of human breast carcinomas by differential PCR. The combined use of differential PCR and automated HPLC analysis of the PCR products may well substitute for classical Southern blot hybridization in routine clinical analysis of oncogene amplification.

Base Sequence↗

[Retinal photocoagulation with a pulsed, frequency-doubled Nd:YAG laser (532 nm)].

The small difference in wavelength between an argon laser (514 nm) and a frequency-doubled Nd:YAG laser (532 nm), together with the advantage of the solid-state technology, makes the Nd:YAG laser likely to play a major role in retinal photocoagulation in the near future. For technical reasons all frequency-doubled Nd:YAG lasers work in a quasi-continuous mode, emitting a burst of highly repetitive short laser pulses during the exposure time desired. We investigated the side effects due to high peak irradiances of those short laser pulse trains (Crystal Focus Nd:YAG laser, Emerald; pulse duration 1-10 microseconds, repetition rate 13 KHz) in rabbits in comparison with a standard argon laser system (Zeiss, Visulas, Argon II). The energy necessary for blanching the retina was similar in both cases. As opposed to the argon laser system, subretinal bubbles were regularly visible ophthalmoscopically with the Nd:YAG system, when average powers as high as 200 mW were used. The ED50 power for bubble formation is about 2-3 times above the ED50 power for blanching. Thermal calculations show that this bubble formation effect is likely to be related to the peak power of the short pulses. The hemorrhage threshold is similar in both systems. However, light microscopically there is no difference between the two laser systems. Panretinal photocoagulation (300-500 microns, 100-200 ms) in patients with proliferative diabetic retinopathy produced such bubbles about once per 1000 lesions.

Animals↗

Comparison of the erbium-yttrium aluminum garnet and carbon dioxide lasers for in vitro bone and cartilage ablation.

The in vitro bone- and cartilage-ablation characteristics of the solid-state erbium:yttrium aluminum garnet laser were compared to those of the carbon dioxide laser. Ablations of fresh, frozen cadaver septal cartilage and maxillary sinus bone were performed using total energies between 1 and 6 J. Specimens were studied using hematoxylin and eosin stain and digitized, computer-assisted measurements of 35-mm photographs. Erbium-yttrium aluminum garnet-ablated bone averaged 5 microns of adjacent tissue thermal injury, compared with 67 microns with carbon dioxide-ablated bone. Erbium-yttrium aluminum garnet-ablated cartilage averaged 2 microns of adjacent tissue thermal injury, compared with 21 microns with the carbon dioxide-ablated cartilage. The tissue-ablation characteristics of the erbium-yttrium aluminum garnet laser are promising for future otolaryngologic applications.

Aluminum↗

Fluorescence lifetime imaging microscopy: homodyne technique using high-speed gated image intensifier.

In the previous sections we demonstrated imaging of intracellular Ca2+ using our approach to FLIM. What other analytes can be imaged using FLIM? We have now characterized the lifetime of a good number of ion indicators. Based on these studies we know that Cl- can be imaged using FLIM with probes such as SPQ or MQAE, pH can be imaged using resorufin and probes of the SNAFL and SNARF (Molecular Probes) series, and Mg2+ can be imaged using Magnesium Green, Mag-quin-2, or Mag-quin-1 (Molecular Probes). At present, the probe for K+, as PBFI, are just adequate as a lifetime probe, but it seems likely that newer probes for Na+ (Sodium Green) and K+ will be practical for effective imaging. Of course, imaging of oxygen is possible using a wide variety of fluorophores. It should be noted that a wide variety of substances and/or phenomena are known to alter decay times, acting as quenchers. These include the phenomena of resonance energy transfer, collisional quenching, temperature effects, and viscosity effects. Also, the FLIM method is not limited to microscopic objects but can be possibly used in remote imaging of any object. Hence, FLIM will allow the imaging of the chemical and physical properties of objects based on the effects of the local environment on the decay kinetics of fluorophores. The instrumentation for FLIM is presently complex and requires a moderately complex laser source, a gain-modulated image intensifier, and a slow-scan CCD camera. However, one can readily imagine the instrumentation becoming rather compact, and even all solid-state, owing to advances in laser and CCD technologies and, more importantly, advances in probe chemistry. To be specific, the dye laser shown in Fig. 1 may be replaced by a simpler UV laser, such as the 354 nm HeCd laser which has become available (Fig. 11). Intensity modulation of a continuous wave sources can be accomplished with acoustooptic modulators. The scientific slow-scan CCD cameras are presently rather expensive, but they are used in the present instrumentation because of their linearity and high dynamic range. However, the increasing use of CCD detectors suggest that even the scientific-grade CCD cameras will soon become less costly. Additionally, the frame rates of these detectors continue to increase in response to the need for faster imaging. Furthermore, the performance of the video CCD cameras is increasing, as seen by the introduction of 10-bit video analog-to-digital (A/D) converters.(ABSTRACT TRUNCATED AT 400 WORDS)

Aminoquinolines↗

[Possible applications of laser in otorhinolaryngology].

Laser therapy in otolaryngology--head and neck surgery using laser types working in the range of the visible and infrared part of the electromagnetic spectrum is well established. The laser types usually employed for micro- and macrosurgery of the aero-digestive tract and for microsurgery of the middle ear, involving thermal ablation of tissue and extensive areas of damage are described, as well as recent advances in laser technology for future use. The mechanisms by which non-thermal, photo-ablative pulsed solid-state crystal infrared and UV-excimer lasers and photodynamic therapy affect biological tissues are reported. The advantageous main areas of application of the different types of laser according to their physical properties are compared on the basis of the results of our own studies and the relevant literature.

Animals↗

Lithotripsy with a Q-switched alexandrite laser system. Preliminary in vivo and in vitro results.

An alexandrite laser system which emits a wavelength of 750 nm, has recently been proposed as a substitute for the pulsed-dye laser (504 nm) for laser lithotripsy. We have carried out in vitro lithotripsy trials in order to evaluate the efficiency of a flashlamp pumped Q-switched alexandrite laser. In the first experiment, we compared the Q-switched alexandrite laser to the pulsed-dye laser with respect to their effectiveness in fragmentizing urinary and model stones (HMT target stones). In the second experiment, we evaluated the effect of Q-switched alexandrite radiation on the urinary wall (bladder, ureter, renal pelvis and liver) of animals (Wistar rats and rabbits) under general anesthesia. In conclusion, the alexandrite laser system is comparable to the pulsed dye laser. The 750-nm wavelength involves minimal risk of damage to the urinary tract and constitutes a safe alternative, especially during blind lithotripsy. It is a compact solid-state system, with no toxic chemical agents as laser material.

Animals↗

Chiral detection in high-performance liquid chromatography by vibrational circular dichroism.

A novel chiral detector for high-performance liquid chromatography has been developed. This detector is based on the measurement of circular dichroism of chiral effluents in the infrared region, i.e., vibrational circular dichroism (VCD). In this instrument, a solid-state spectral tunable (from 2.4 to 3.5 microns) F-center laser was used as the light source. The linearly polarized laser beam was converted into left circularly polarized light (LCPL) and right circularly polarized light (RCPL) at 42 kHz by means of a photoelastic modulator. The intensity of the LCPL and RCPL transmitted through the sample was measured by a liquid nitrogen cooled indium antimonide detector. Double modulation was employed to reduce the noise associated with the laser beam. Specifically, the linearly polarized laser beam, prior to being converted to CPL, was modulated at 85 Hz by a mechanical chopper. Demodulation and amplification were accomplished with the use of two lock-in amplifiers. In its present configuration, the instrument can be used to measure the VCD of O-H groups. Its sensitivity is so high that it was able, for the first time, to detect chirally (with limits of detection of micrograms) (R)- and (S)-2,2,2-trifluoro-1-(9- anthryl)ethanol and (R)- and (S)-benzoin when these compounds were chromatographically separated from the corresponding racemic mixtures by a Chiralcel-OD column. The main advantage of this chiral detector is, however, its universality; i.e., it can be used to virtually detect any chiral compounds which has O-H group (e.g, aliphatic alcohols such as 2-octanol).

Chromatography, High Pressure Liquid↗

A new method for characterizing beta-ray ophthalmic applicator sources.

A technique is described which enables one to obtain detailed dose characteristics of 90Sr beta-ray ophthalmic applicators. A radiochromic radiation detector which is a solid-state solution of hexahydroxyethyl pararosaniline cyanide in a nylon polymer (i.e., thin foil), has been used to determine the surface dose rate and dose distribution of these sources. The detectors are rugged, easily handled, have an equivalent response (optical density per unit absorbed dose) to photons and electrons, and produce high-resolution images. They have been found useful for this application due to the high surface dose rates [0.10-1.0 Gy (H2O)/s] and their low sensitivity (approximately 10(4) Gy for an optical density of 1.0). The foils have been evaluated on a He-Ne scanning laser densitometer with a resolution of 0.3 mum. Comparison with NIST (formerly NBS) extrapolation ionization chamber measurements indicates surface dose-rate agreement within 6%. Spectral dosimetric characteristics are presented and discussed.

Beta Particles↗

Transition dipole orientations in the early photolysis intermediates of rhodopsin.

The linear dichroism spectrum of rhodopsin in sonicated bovine disk membranes was measured 30, 60, 170, and 600 ns after room temperature photolysis with a linearly polarized, 7-ns laser pulse (lambda = 355 or 477 nm). A global exponential fitting procedure based on singular value decomposition was used to fit the linear dichroism data to two exponential processes which differed spectrally from one another and whose lifetimes were 42 +/- 7 ns and 225 +/- 40 ns. These results are interpreted in terms of a sequential model where bathorhodopsin (BATHO, lambda max = 543 nm) decays toward equilibrium with a blue shifted intermediate (BSI, lambda max = 478 nm). BSI then decays to lumirhodopsin (LUMI, lambda max = 492 nm). It has been suggested that two bathorhodopsins decay in parallel to their products. However, a Monte Carlo simulation of partial photolysis of solid-state visual pigment samples shows that one mechanism which creates populations of BATHO having different photolysis rates at 77 K may not be responsible for the two decay rates reported here at room temperature. The angle between the cis band and 498-nm band transition dipoles of rhodopsin is determined to be 38 degrees. The angles between both these transition dipoles and those of the long-wave-length bands of BATHO, BSI, and LUMI are also determined. It is shown that when BATHO is formed its transition dipole moves away from the original cis band transition dipole direction. The transition dipole then moves roughly twice as much towards the original cis band direction when BSI appears. Production of LUMI is associated with return of the transition dipole almost to the original orientation relative to the cis band, but with some displacement normal to the plane which contains the previous motions. The correlation between the lambda max of an intermediate and its transition dipole direction is discussed.

Animals↗