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At least 19 recordsLinked to original sources
PubMed1999

Cutaneous side effects from laser treatment of the skin: skin cancer, scars, wounds, pigmentary changes, and purpura--use of pulsed dye laser, copper vapor laser, and argon laser.

It has been the intention of this thesis to increase the knowledge on the development of cutaneous side effects from treatment with the argon laser, the copper vapor laser, and the pulsed dye laser, which represent technical developments within laser systems used for treatment of vascular lesions. To reach that goal, the investigations focused on patient and lesional characteristics (skin pigmentation, skin redness, and epidermal thickness) and on the importance of UV irradiation before and after dermatological laser treatment. The aspect of UV irradiation was added because vascular lesions frequently involve the face and, therefore, may be exposed to sunlight in relation to laser treatment. Risk assessments were performed on clinically visible side effects in order to improve the preoperative information to the patients about their individual risks of obtaining side effects from dermatological laser treatment. The laser-induced side effects were evaluated by systematic clinical assessments, by histological and biochemical examinations, by skin reflectance measurements, optical profilometry, and ultrasonography. The term side effects is associated with both transient and permanent skin reactions such as purpura, wounds, textural changes, scars, pigmentary changes, and squamous cell carcinomas. Lightly pigmented, hairless hr/hr C3H/Tif mice, hairless, albino hr/hr MORO/Ibm mice, human, healthy volunteers, and children with port-wine stains were included in the studies. This thesis represents the first systematic and experimental approach to selected side effects from laser treatment of the skin. The argon laser (AL) and the copper vapor laser (CVL) The results from AL and CVL treatments are described together because these lasers are continuous/quasicontinuous lasers that do not meet the requirements for selective photothermolysis, which represents the most selective delivery of energy to cutaneous vessels. In normal-skinned human volunteers, the postoperative development of scars and pigmentary alterations depended on the preoperative constitutive skin pigmentation degree. Significant correlations were found between the preoperative skin pigmentation and the clinically scored pigmentary changes and scarring 1, 2, and 6 months postoperatively, indicating that dark-pigmented skin types respond with more heavy skin reactions than fair-pigmented skin types. Pigmentary changes occurred at lower intensity levels than scarring. No difference was seen between the AL and the CVL concerning the risk of inducing these side effects. In hairless, albino hr/hr MORO/Ibm mice increasing epidermal thicknesses reduced CVL-induced wounds and scars. Significant negative correlations were found between preoperative epidermal thicknesses and CVL-induced skin reactions. In lightly pigmented, hairless hr/hr C3H/Tif mice, CVL treatment induced an increase in skin pigmentation, evaluated by a semiquantitative technique. Postoperative UV irradiations with simulated solar UV increased the CVL-induced skin pigmentation additionally. The size of CVL-induced wounds and scars tended to enlarge by preoperative UV irradiations. In contrast, CVL-induced wounds were diminished and had a prolonged wound healing time when postoperative UV irradiations were given. This may indicate a deep constricted skin damage. Moreover, the histologically evaluated fibrosis and the frequency of bulging infiltration were increased by postoperative UV irradiation. When taking the liberty to extend the obtained results from the animal studies to humans, these results support the importance of pre- and postoperative sunprotection. Regarding skin cancer, in hairless mice it was found that one treatment with the CVL did not have a malignant potential itself. Pretreatment with the CVL at the highest intensity level (1.4W) delayed UV-induced photocarcinogenesis significantly. The pulsed dye laser (PDL) The PDL is described separately because it is the only laser in this thesis that fulf

Adult↗
PubMed1999

Treatment of atrophic facial scars with combined use of high-energy pulsed CO2 laser and Er:YAG laser: a practical guide of the laser techniques for the Er:YAG laser.

BACKGROUND: Although CO2 laser resurfacing provides substantial clinical improvement for atrophic facial scars, the CO2 laser often results in excessive thermal damage to the skin. It increases complications postoperatively. The Er:YAG laser ablates thinner layers of tissue than the CO2 laser with minimal thermal damage to the surrounding skin. OBJECTIVE: To determine the efficacy of combined treatment of atrophic facial scars with high-energy pulsed CO2 laser and Er:YAG laser. METHODS: One hundred fifty-eight patients were treated with a combination of high-energy pulsed CO2 laser and Er:YAG laser for atrophic facial scars. All patients were evaluated after 3 months of treatment. RESULTS: The scars improved 80-89% in 65 patients, 70-79% in 56 patients, more than 90% in 32 patients, 60-69% in 2 patients, and less than 60% in 3 patients after laser treatment. CONCLUSION: Treatment of atrophic facial scars with combined use of high-energy pulsed CO2 laser and Er:YAG laser is a very effective and useful method.

Adult↗
PubMed2002

Laser-assisted surgery addressing snoring long-term outcome comparing CO2 laser vs. CO2 laser combined with diode laser.

Our study encompasses 61 patients (49 men--80.3%; 12 women--19.7%) treated from September 1998 through August 2001. Mean follow-up covers 25 months (range: 7-43 months). Our CO2-LAUP technique involves vaporizing the palatine mucosa along a rectangular surface from the palatal dimple to the base of the uvula; trimming the palatine arches under the velum; and resecting the uvula. For 22 patients, we employed intravelar diode laser coagulation in the expectation of reducing the postoperative pain whilst achieving the same therapeutic effectiveness. There is no pain difference between the CO2-LAUP technique versus that combining intravelar diode laser coagulation with CO2 laser uvula resection and trimming of the palatine arches. Mean maximal pain reaches 6.93 +/- 3.55 with CO2 laser and 6.95 +/- 3.64 with CO2 laser plus diode laser. Similarly, both techniques involve the same mean algesic period of 22 days with the day of maximal pain at 1 week after surgery. Associating base of tongue vaporization significantly increases the algesic period (p = 0.042). No long-term complications were observed in relation to intravelar coagulation or LAUP, whether combined or not with base of tongue vaporization. In terms of patients satisfaction, no significant difference exists between the various surgical techniques of the velum alone. The satisfaction rate reaches 5.26 +/- 3.92 with CO2 laser and 5.82 +/- 2.67 with the CO2 laser plus diode laser. Satisfaction is statistically identical when base of tongue vaporization is included in the procedure.

Female↗
PubMed1995

Dye laser treatment of port-wine stains: comparison of the continuous-wave dye laser with a robotized scanning device and the pulsed dye laser.

BACKGROUND: Despite good results in the treatment of most port-wine stains (PWS) with continuous-wave visible-light lasers, light PWS and those in certain locations respond less favorably and have a higher risk of scarring. Robotized scanning devices such as the Hexascan device have been developed for continuous-wave laser sources to produce greater target specificity, to increase reproducibility of results, and to decrease the incidence of adverse effects. OBJECTIVE: The purpose of this study was to compare the effects of the same wavelength of light (585 nm) on test sites within PWS with the flashlamp-pumped pulsed dye laser and a continuous-wave tunable dye laser scanned through a Hexascan robotized scanning device. METHODS: Two adjacent, noncontiguous sites within PWS were treated in 29 patients, one site with the flashlamp-pumped pulsed dye laser and the other with an argon-pumped continuous-wave tunable dye laser affixed to a Hexascan device. RESULTS: Twenty-eight patients completed the study. The pulsed dye laser was found to be superior to the continuous-wave dye laser with the Hexascan device in 45% of patients, whereas the continuous-wave tunable dye laser with the Hexascan device was considered superior in 15%. There was no difference in the remaining 40%. Undesirable side effects were infrequent with both treatments. There was no significant difference in hypopigmentation or atrophic and hypertrophic scarring, but hyperpigmentation was more frequent with the continuous-wave dye laser with the Hexascan device. CONCLUSION: Both the pulsed dye laser and continuous tunable-wave dye laser with the Hexascan device produce slight lightening after one treatment. The pulsed dye laser produces slightly greater lightening than the continuous-wave tunable dye laser with the Hexascan device 6 weeks after treatment of test areas within PWS in 40% of those treated. It also produced slightly less hypopigmentation and hyperpigmentation.

Adolescent↗
PubMed1996

Comparison of argon laser iridotomy and sequential argon laser and Nd:YAG laser iridotomy in dark irides.

BACKGROUND AND OBJECTIVE: A prospective study was performed to compare argon laser iridotomy and sequential argon laser and Nd:YAG laser iridotomy in dark irides. PATIENTS AND METHODS: Twenty-four eyes of 17 patients underwent laser iridotomies; 13 underwent argon laser iridotomies and 11 underwent sequential argon laser and Nd:YAG laser iridotomies. The argon laser settings were standardized at 1.2 W, 50-mum spot size, and 0.1-second duration. The Nd:YAG laser was set at 2.5 mJ and single-pulse shots were used. RESULTS: All of the iridotomies were patent at the end of one treatment session. The mean total energy used for argon laser iridotomy was 8.28 J. For sequential iridotomy, 3.12 J was used for the argon laser stage and 7.5 mJ for the Nd:YAG laser stage. CONCLUSION: The total argon laser energy used can be reduced by 2.65 times by using the sequential laser iridotomy technique.

Aged↗
PubMed1995

The Glaucoma Laser Trial (GLT) and glaucoma laser trial follow-up study: 7. Results. Glaucoma Laser Trial Research Group.

PURPOSE: To determine differences between the two treatment groups of the Glaucoma Laser Trial with respect to intraocular pressure, visual fields, optic disk cupping, and therapy for primary open-angle glaucoma. METHODS: The Glaucoma Laser Trial was a multicenter, randomized clinical trial designed to assess the efficacy and safety of starting treatment for primary open-angle glaucoma with argon laser trabeculoplasty vs starting with topical medication. The Glaucoma Laser Trial Follow-up Study was a follow-up study of 203 of the 271 patients who enrolled in the Glaucoma Laser Trial. By the close of the Glaucoma Laser Trial Follow-up Study, median duration of follow-up since diagnosis of primary open-angle glaucoma was seven years (maximum, nine years). RESULTS: Over the course of the Glaucoma Laser Trial and Glaucoma Laser Trial Follow-up Study, the eyes treated initially with argon laser trabeculoplasty had lower intraocular pressure and better visual field and optic disk status than their fellow eyes treated initially with topical medication. As compared to eyes initially treated with medication, eyes initially treated with laser trabeculoplasty had 1.2 mm Hg greater reduction in intraocular pressure (P < .001) and 0.6 dB greater improvement in the visual field (P < .001) from entry into the Glaucoma Laser Trial. The overall difference between eyes with regard to change in ratio of optic cup area to optic disk area from entry into the Glaucoma Laser Trial was -0.01 (P = .005), which indicated slightly more deterioration for eyes initially treated with medication. CONCLUSIONS: Initial treatment with argon laser trabeculoplasty was at least as efficacious as initial treatment with topical medication.

Administration, Topical↗
PubMed1993

Infrared laser soft tissue ablation versus ultraviolet excimer laser. Experimental introduction of the Hol:YAG-laser in oral surgery.

The in vivo tissue ablation characteristics of a pulsed infrared laser (Hol:YAG, lambda = 2120 nm) and a pulsed excimer laser (XeCl, lambda = 308 nm) were studied in an animal model. Laser energy was delivered via nylon fibers for the Hol:YAG laser and via quartz fibers for the excimer laser. Laser incisions were made under precise reproducible conditions on the sublingual side of the tongue and the gingiva of white rats. Laser surgery was done at two different energy output settings for the Hol:YAG laser and at one setting for the excimer laser. Histologic studies revealed tissue defects with clean contours for both laser types with small zones of necrosis of the adjacent tissue (Hol:YAG: 180 microns to 640 microns; excimer: 40 microns to 160 microns) and without carbonization. Both laser types function on the principal of photoablation and permit excellent control of tissue ablation. Wound healing was studied over a 10-day period and showed complete wound closure by re-epithelialization. The in vivo tissue ablation characteristics and the surgical reliability of the two lasers are compared and discussed with respect to oral and periodontal surgery.

Animals↗
PubMed2001

Laser resurfacing with a long pulse erbium:YAG laser compared to the 950 ms pulsed CO(2) laser.

BACKGROUND AND OBJECTIVE: Laser resurfacing with the 950 micros pulsed CO(2) laser is an effective treatment for photodamage and acne scarring; however, the potential for prolonged erythema and delayed re-epithelialization dissuade many patients from the procedure. With the use of erbium lasers alone, there is a decrease in the incidence and severity of these adverse sequelae; however, it is difficult to achieve the same degree of improvement as with the CO(2) laser because of the more superficial depth of resurfacing. Thus, new erbium lasers have been developed with longer pulse durations to deliver increased thermal effects to tissue. It is hypothesized that with the use of these lasers, diminished erythema and faster wound healing will be observed as well as enhanced clinical outcomes. STUDY DESIGN/MATERIALS AND METHODS: Sixteen patients were randomized to receive laser resurfacing on one-half of the face with the 950 micros pulsed CO(2) laser (UPCO(2)) followed by short pulse erbium:YAG ablation, and to the other half with a variable pulsed erbium laser (VP Er:YAG) followed by traditional short pulse erbium laser. Patients were evaluated clinically before resurfacing and at 1, 2, 4, 8, and 12 weeks post-operatively. Histologic samples taken at various time periods before and after resurfacing were also evaluated. RESULTS: Overall clinical improvement was equal for both UPCO(2) and VP Er:YAG treated sides with an average improvement in photoaging scores of 57%. Decreased erythema, less edema, and faster healing were observed on the VP Er:YAG treated side. CONCLUSION: The VP Er:YAG laser can achieve a similar degree of improvement as seen with short pulse CO(2) laser resurfacing with decreased thermal tissue effects and decreased risk for adverse sequelae.

Face↗
PubMed1998

Laser scar revision: comparison of CO2 laser vaporization with and without simultaneous pulsed dye laser treatment.

BACKGROUND: Over the past decade, the 585-nm pulsed dye laser (PDL) has been used successfully to treat a variety of cutaneous vascular lesions as well as hypertrophic scars. Laser scar revision has been revolutionized by the recent development of high-energy, pulsed carbon dioxide (CO2) laser systems. These new CO2 lasers allow controlled vaporization of thin layers of skin while minimizing damage to surrounding dermal structures. OBJECTIVE: To determine the effect of a high-energy, pulsed CO2 laser alone and in combination with a 585-nm PDL on nonerythematous hypertrophic scars. METHODS: Twenty patients with nonerythematous hypertrophic scars were treated with a high-energy, pulsed CO2 laser. One-half of each scar was additionally treated with the 585-nm PDL laser. Sequential clinical and photographic analyses were performed independently by two blinded assessors. In addition, erythema reflectance spectrometry measurements were obtained from the scars before and at regular postoperative intervals. RESULTS: Global assessment scores and erythema spectrometry measurements were significantly improved after laser treatment. Combination CO2 and PDL laser treatment resulted in more significant improvement than CO2 laser irradiation alone. CONCLUSION: Concomitant use of the high-energy, pulsed CO2 and PDL laser systems was superior to CO2 laser vaporization alone for revision of nonerythematous hypertrophic scars. Once again, the vascular specificity of the 585-nm PDL has been linked to improvement in hypertrophic scar tissue.

Adolescent↗
PubMed1995

[Comparative study on frequency-doubled Nd: YAG laser, krypton laser and diode laser photocoagulation for diabetic maculopathy].

Twenty six eyes of thirteen patients with diabetic maculopathy (Fukuda's classification AI, AII, BI) were treated with frequency-doubled Nd:YAG laser (6 eyes) or krypton laser (7 eyes) in one eye and diode laser (13 eyes) in the other eye. Group A was treated with frequency-doubled Nd: YAG laser and diode laser, and group B was treated with krypton laser and diode laser. The visual acuity, visual field (Octopus program 31) and fundus were examined at one month, 3 months, and 6 months after photocoagulation. Visual acuity was stable in all eyes. The central 30 degree visual sensitivity decreased more after diode laser treatment than after that of the other lasers. Krypton laser photocoagulation maintained the better visual function and was easy to use followed by frequency-doubled Nd: YAG laser. Because the appearance immediately after diode laser lesion was weaker than one hour after coagulation, it was difficult to get the proper power setting.

Adult↗
PubMed1989

[Use of the thermal laser effect of laser irradiation for cardiovascular applications exemplified by the Nd:YAG laser].

Techniques of percutaneous transluminal application of laser energy for vessel recanalization have been used clinically since 1983. The commonly used Nd:YAG and argon lasers achieve ablation of atherosclerotic plaques by thermal action (vaporization). In order to reduce undesirable thermal damage in the neighborhood of the target tissue and to avoid vessel perforation, optimal irradiation parameters, modified (atraumatic) fiber tips (hot tips, sapphires), and steerable catheter systems needed to be implemented. Favorable results from peripheral application have encouraged use in the coronary circulation. More recently, coagulative tissue effects of circumferential irradiation of the vessel wall during balloon dilatation have been used for stabilization of acute and late results after mechanical balloon angioplasty. Enhancement of the differential light absorption of atherosclerotic plaque by use of biological dyes may further improve selective intravascular laser application. Intraoperative ECG-guided laser coagulation of arrhythmogenic areas of myocardium is a method for treatment of malignant arrhythmias. Transluminal non-operative application of myocardial laser photocoagulation has now been tested experimentally and shown to be safe and effective. There was no arrhythmogenicity or thermal damage of coronary arteries associated with this method. Innovative techniques such as nanosecond pulsed excimer lasers (athermal action) and development of "intelligent" lasers--which are equipped with spectroscopy-guided feedback systems for plaque recognition--have opened new perspectives and will further improve safety and efficacy of clinical laser application. However, according to current experience, the thermally acting Nd:YAG laser is an effective and versatile mode of laser therapy for selected cardiovascular indications.

Angioplasty, Balloon↗
PubMed1988

The pulsed dye laser versus the Q-switched Nd:YAG laser in laser-induced shock-wave lithotripsy.

To date, there are two fairly well-established alternatives for laser-induced shock-wave lithotripsy in clinical practice. The Q-switched Nd:YAG laser is distinguished by the high-stone selectivity of its coupler systems. The necessity of a coupler system and its fairly small conversion rate of light energy into mechanical energy present serious drawbacks. Furthermore, the minimal outer diameter of the transmission system is 1.8 mm. The pulsed-dye laser can be used with a highly flexible and uncomplicated 200-micron fiber. However, the laser system itself is more complicated than the Q-switched Nd:YAG laser and requires a great deal of maintenance. Biological evaluation of damage caused by direct irradiation shows that both laser systems produce minor damage of different degrees. YAG laser lithotripsy with the optomechanical coupler was assessed in 31 patients with ureteral calculi. The instability and limited effectiveness of the fiber application system necessitated auxiliary lithotripsy methods in 14 cases. Dye-laser lithotripsy is currently being tested in clinical application. Further development, such as systems for blind application or electronic feedback mechanisms to limit adverse tissue effects, have yet to be optimized. Nevertheless, laser-induced shock-wave lithotripsy has the potential to become a standard procedure in the endourologic management of stone disease.

Animals↗
PubMed2000

In vivo model of histologic changes after treatment with the superpulsed CO(2) laser, erbium:YAG laser, and blended lasers: a 4- to 6-month prospective histologic and clinical study.

BACKGROUND AND OBJECTIVE: To compare the in vivo histologic effects of the pulsed carbon dioxide (CO(2)) and erbium:ytrium aluminum garnet (Er:YAG) lasers and to assess the effects of combining CO(2) and Er:YAG laser modalities during a single treatment session. We previously reported 10 patients treated with four laser regimens: CO(2) alone, CO(2)/Er:YAG, Er:YAG alone, Er:YAG/CO(2) with time points at 1 hour and 7 days between laser treatment and histologic analysis. This study found that the optimal treatment consisted of limited CO(2) laser passes followed by Er:YAG. This treatment produced less collagen injury, less thermal necrosis, and more robust epithelial and dermal fibrous tissue regeneration in the acute phase of healing. The present study examines the histologic changes resulting from the host healing response to laser treatment on long-term follow-up of 4-6 months. STUDY DESIGN/MATERIALS AND METHODS: The Stanford University Committee on Human Subjects in Medical Research approved this study. Nine patients with actinic damage and indications for rhytidectomy volunteered for this interventional study in which each patient served as both experimental and control. The right preauricular area was treated at five sites with the following: (1) CO(2), (2) CO(2) followed by Er:YAG, (3) Er:YAG, (4) blended CO(2)/Er:YAG (Derma-Ktrade mark), (5) phenol. Each was subjected to full-face or sub-unit treatment. Each patient was followed up initially daily then weekly for healing of the full-face laser and for differences in healing of the five treatment areas. Five patients were selected for histologic evaluation. At 4-6 months, these patients underwent rhytidectomy with immediate removal of laser-treated skin, which was evaluated histologically by the study dermatopathologist, who was blinded to the treatment at each site. RESULTS: CO(2) laser treatment produced the greatest thickness of neocollagen (0.27 mm; P < 0.05), the highest neocollagen density (P < 0.05), the greatest decrease in elastosis (27%), but took the longest time for healing and resolution of erythema and inflammation (up to 6 months). Er:YAG used alone produced the least collagen density, with the thinnest band of neocollagen (0.08 mm), but the most rapid resolution of erythema and inflammation (within 10 days). Combined CO(2)/Er:YAG treatments, including Derma-Ktrade mark and CO(2) followed by Er:YAG produced histologic changes that were intermediate, as well as recovery that was intermediate (resolution of erythema within 1 month); the development of neocollagen was greater in CO(2)-containing modalities than Er:YAG used alone by a statistically significant margin (P = 0.001). These histologic findings were corroborated by clinical correlation by examination of the five treatment spots in nine patients and in full-face treatments in 100 patients. CONCLUSION: Collagenesis is greatest with CO(2) and least with Er:YAG. Elastosis decreased to the greatest degree with CO(2), least with erbium, and to an intermediate extent with blended CO(2)/Er:YAG regimens (sequential and Derma-K). These changes from control are statistically significant with all regimens (P < 0.05). Blended CO(2)/Er:YAG treatments provide an optimal combination of the benefits of CO(2) but with lesser erythema and healing delay. Clinical and histologic findings change over time for different treatments. Thus, long-term histology is critical for predicting results of treatment.

Algorithms↗
PubMed2001

Novel laser system and laser irradiation method reduced the risk of carbonization during laser interstitial thermotherapy: assessed by MR temperature measurement.

BACKGROUND AND OBJECTIVE: To establish laser interstitial thermotherapy (LITT) for intracranial tumors, the authors investigated a method to regulate localized temperature generated by interstitial laser irradiation using magnetic resonance (MR) temperature mapping. STUDY DESIGN/MATERIALS AND METHODS: A diode laser system and six different types of optical-fiber system were developed for LITT. The characteristics of temperature profiles produced by each laser-fiber system were investigated with MR temperature measurement (the water proton chemical technique), and differences in the temperature profile induced by two laser-irradiation methods (continuous and intermittent) were observed. RESULTS: All fiber systems with the exception of the diffuse-projection fiber system, created a spherical temperature profile. Carbonization sometimes occurred around the bare-end fiber tip upon high power laser irradiation. The diffuse-projection fiber system produced a cylindrical temperature distribution, and the temperature profile showed a more gradual temperature elevation than the bare-end fiber. No carbonization occurred at the tip of the diffuse-projection fiber system. In addition, the utilization of the intermittent irradiation method also increased temperature gradually. Fiber-system modification and intermittent irradiation reduced laser-beam intensity and the risk of carbonization. CONCLUSION: The use of a diffuse-projection fiber system which intermittently transmits a reduced intensity laser beam is an effective tool to regulate temperature during LITT using MR temperature measurement.

Animals↗
PubMed1997

Are contact laser, interstitial laser, and transurethral ultrasound-guided laser-induced prostatectomy superior to transurethral prostatectomy?

BACKGROUND: In order to assess the value of various new therapeutic modalities in the management of benign prostatic hyperplasia (BPH), we performed a prospective study comparing transurethral resection of the prostate (TURP) to contact Laser, interstitial Laser, and transurethral ultrasound-guided laser-induced prostatectomy (TULIP). METHODS: The following parameters were evaluated preoperatively as well as 3, 6, and 12 months after surgery: prostatic volume, urinary flow rate, postvoid residual volume, and the AUA symptom score. The diagnosis of bladder outlet obstruction was established preoperatively by means of pressure/flow studies which were repeated 1 year after the operation. RESULTS AND CONCLUSIONS: In conclusion, TURP is still the gold standard in the treatment of BPH. The results of TULIP, contact laser, and interstitial laser are about the same. The time intervals within which the patients become free of symptoms, however, vary widely. Contact laser is limited to prostates below 50 cc, while interstitial laser is ideal for patients in poor general health who present with large prostates. Furthermore, our results demonstrate that the only reliable data for determining the degree of posttherapeutic disobstruction can be provided by urodynamic investigations including pressure/flow diagrams.

Humans↗
PubMed2000

Influence of the laser fluence in infrared matrix-assisted laser desorption/ionization with a 2.94 microm Er : YAG laser and a flat-top beam profile.

The dependence of the signal intensity of analyte and matrix ions on laser fluence was investigated for infrared matrix-assisted laser desorption/ionization (IR-MALDI) mass spectrometry using a flat-top laser beam profile. The beam of an Er : YAG laser (wavelength, 2.94 microm; pulse width, 90 ns) was coupled into a sapphire fiber and the homogeneously illuminated end surface of the fiber imaged on to the sample by a telescope. Three different laser spot sizes of 175, 350 and 700 microm diameter were realized. Threshold fluences of common IR matrices were determined to range from about 1000 to a few thousand J m(-2), depending on the matrix and the size of the irradiated area. In the MALDI-typical fluence range, above the detection threshold ion signals increase strongly with fluence for all matrices, with a dependence similar to that for UV-MALDI. Despite the strongly different absorption coefficients of the tested matrices, varying by more than an order of magnitude at the excitation laser wavelength, threshold fluences for equal spot sizes were found to be comparable within a factor of two. With the additional dependence of fluence on spot size, the deposited energy per volume of matrix at threshold fluence ranged from about 1 kJ mol(-1) for succinic acid to about 100 kJ mol(-1) for glycerol.

Angiotensin I↗
PubMed1999

Laser shaping of corneal transplants in vitro: area ablation with small overlapping laser spots produced by a pulsed scanning laser beam using an optimizing ablation algorithm.

Area laser lathing and trephination of donor corneas is used to produce different types of grafts for human transplantation. 193 nm (ArF excimer) laser radiation is used, since this is known to give a non-thermal laser-tissue interaction with a minimal zone of tissue damage. To guarantee the highest degree of flexibility concerning the overall shape of the grafts as well as their thickness profiles, we use a small (compared with the area to be ablated) scanning laser spot. For area lathing of the tissue we have developed a new ablation algorithm (optimized scanning laser ablation, OSLA) that can be applied to lathe and perforate any tissue--with concave (as in this application), convex or plane surface geometry--where surface precision and smoothness are key issues. Using OSLA with the Excimer Laser Corneal Shaping System (a tool for in vitro fabrication of all kinds of corneal transplants like donor buttons for keratoplasty, lamellar grafts for epikeratoplasty and refractive lenticules) enabled us to produce all types of corneal grafts with very high precision. This is considered to be a major improvement towards the production of refractive lenticules.

Algorithms↗