Laser Center Research Articles

The Effect of 3 Sessions of Q Switched Neodymium: Yttrium?Aluminum?Garnet Laser in the Treatment of Freckles

Background: Freckles are common superficial pigmented lesions which can become cosmetic problems. Advances in laser technology have resulted in the ability to treat pigmented lesions with greater safety and efficacy. Objective: The study aimed to evaluate the effectiveness of 1,064 nm Q-switched neodymium: yttrium–aluminum– garnet (Nd- YAG) laser in the treatment of freckles. Methods: Fifty patients with freckles referring to the laser centers of Al-Azhar University hospital (Asyut) were enrolled in this open-label, monocentric study. All participants received 3 sessions of 1,064-nm Q switched Nd:YAG laser at 4-weeks intervals. The pigmentation area and severity index (PSI score) was calculated based on 3 parameters: Area, darkness, and density of the pigmented lesions. Results: Fifty patients (4 males and 46 females) completed the study protocol. The age of the patients ranged from 6-43 years, the duration of freckles showed a wide range, (1 month-20 years) with a mean duration of 5.13 ± 4.72 years. There was a statistical significant improvement in mean PSI after treatment of freckles with 1064 Q-Switched Nd-YAG. Excellent improvement (≥75%) were occurred in 17 cases (34%), very good improvement (50-74%) in 14cases (28%), good improvement (≥25-49%) in 16 cases (32%) and poor improvement (<25% lightening) in 3 cases (6%). The correlation between improvement and clinical parameters showed positive significant correlation with duration of disease and number of sessions. The reported side effects among this study were post-inflammatory hyperpigmentation in 2 cases (4%), hypopigmentation in 3 cases (6%) and erythema in 6 cases (12%). Conclusions: 1064 Q-switched Nd- YAG laser is effective modality in the treatment of freckles especially in patients with long duration.

Stable single-polarization single-longitudinal-mode linear cavity erbium-doped fiber laser based on structured chirped fiber Bragg grating

A novel linear cavity erbium-doped fiber (EDF) laser based on a structured chirped fiber Bragg grating (CFBG) filter is proposed for stable single-polarization (SP) single-longitudinal-mode (SLM) operation. For the first time, to the best of our knowledge, a structured CFBG filter with an ultranarrow transmission band which is generated by tapering directly on CFBG is used to select the laser longitudinal mode. The SLM operation is obtained by using the structured CFBG together with an unpumped EDF acting as a saturable absorber. The fluctuations of the laser peak power and center wavelength are less than 0.07dB and 1pm in 1h, respectively. The stable SP operation is achieved by using the inline broadband polarizer. The measured 20dB laser linewidth is about 27.7kHz, which indicates the laser linewidth is approximately 1.39kHz FWHM.

A setup for studies of laser-driven proton acceleration at the Lund Laser Centre

AbstractWe report on a setup for the investigation of proton acceleration in the regime of target normal sheath acceleration. The main interest here is to focus on stable laser beam parameters as well as a reliable target setup and diagnostics in order to do extensive and systematic studies on the acceleration mechanism. A motorized target alignment system in combination with large target mounts allows for up to 340 shots with high repetition rate without breaking the vacuum. This performance is used to conduct experiments with a split mirror setup exploring the effect of spatial and temporal separation between the pulses on the acceleration mechanism and on the resulting proton beam.

Treatment of keloids with laser-assisted topical steroid delivery: a retrospective study of 23 cases.

Topical or intralesional corticosteroids are referred to as gold standard treatments for keloids. Recent studies showed that ablative fractional laser (AFL) treatment facilitates delivery of topical drug deeply into the skin by creating vertical channels. The objective of the present study was to assess the ablative erbium laser in fractionated mode, combined with topical high potent corticosteroid cream for treating resistant keloid scars. We conducted a retrospective study in the laser center of the Department of Dermatology (University Hospital of Nice, France), from January 2010 to June 2012, on patients with keloids who were resistant to a first-line of treatment. A 2940-nm ablative fractional erbium laser was used. Topical betamethasone cream was applied twice a day under occlusion with transparent film dressings. A total of 23 patients with 70 keloids were treated from January 2010 to June 2012. The median percentage of improvement was 50% (range -43 to 84). The mean follow-up was 8 months (range 3-18), and a recurrence was observed for eight lesions (22%). Although this observation warrants a prospective comparative evaluation, it supports the interest of the laser-assisted delivery of steroids for treating keloids scars.

Focused laser lithographic system with sub-wavelength resolution based on vortex laser induced opacity of photochromic material.

A focused laser lithographic system combines with vortex laser induced opacity of photochromic layer to write patterns with linewidth below wavelength. A photochromic layer is formed by coating the mixture of metanil yellow and aqueous PVA solution on the photoresist layer. In our system, the center of a lithographic laser with a 405 nm wavelength coincides with the center of vortex laser with a 532 nm wavelength. When a photochromic layer is illuminated by both lasers simultaneously, the absorbance for the lithographic laser decreases at the hollow region of the vortex laser but increases at its annular region, so that a transparent aperture for the lithographic laser is created and its size could be tuned by changing the power of vortex laser; therefore, the linewidth of written patterns is variable. Experimentally, using a 20× lens (NA = 0.4), this system condenses the linewidth of written patterns from 6614 to 350 nm.

The effectiveness of excimer laser on vitiligo treatment in comparison with a combination therapy of Excimer laser and tacrolimus in an Iranian population

Objectives: Usage of 308-nm excimer laser (EL) is an effective treatment in vitiligo. As genetic predispositions along with type of skin and rate of sun exposure are known factors influencing the treatment outcomes, we tried to evaluate the treatment results of using 308 nm-excimer laser alone in comparison with the combined therapy of EL and topical tacrolimus in Iranian patients with vitiligo. Methods: We reviewed the medical files of 150 patients with vitiligo who were referred to the Behsima Laser Center between April 2012 and April 2013. Seventy five patients who received combined therapy of 308 nm EL and topical tacrolimus three times a week entered the study. Seventy-five controls with matched characteristics and who received only EL were also selected. The amount of repigmentation was estimated by an expert dermatologist and was classified in 5 ranks. Results: In the case group, 33.3% (n: 25) showed 50–75% repigmentaion and 49.3% (n:37) had more than 75% response to therapy, whereas among the patients in the control group 29.3% (n: 22) showed no repigmentation and only 8% (n: 6) demonstrated more than 75% repigmentation response. The higher efficiency of the combination therapy on repigmentation was statistically significant (P: 0.006). Conclusion: Our study shows that Iranian patients with vitiligo who received a combined treatment course with 308-nm EL and tacrolimus 0.1% experienced significantly higher levels of repigmentation in comparison with laser therapy alone.

Correlated scattering: probing atomic structure of molecules and nanoparticles

In 1977, Z. Kam theorized that correlations of scattering patterns, measured by exposing a solution of randomly oriented identical particles to x-ray radiation, could yield detailed information on the internal structure of the individual particles [1]. During a single exposure (whose duration should be short compared to the particle rotational diffusion time), physical correlations arise whenever multiple photons scatter from the same particle into different directions. By averaging correlations from many exposures, we have demonstrated that one can extract this correlated signal from a background of uncorrelated single-direction scattering events from different particles [2]. This additional information can be used to place constraints on model structures of the particles under investigation, providing a method of structure refinement to atomic resolution. We recently observed correlated scattering from solutions of ~10^9 silver nanoparticles exposed to synchrotron radiation at a microfocus beamline at SSRL [2]. By auto- and cross- correlating the Bragg rings 111 and 200, five correlation peaks were resolved corresponding to the structure and symmetry of silver's reciprocal lattice. To transition from nanoparticles to biomolecule studies, we have performed several experiments at x-ray free electron laser centers (SLAC and SPring-8), and are working to refine analysis techniques.

Special Section Guest Editorial: Metamaterials and Photonic Nanostructures

Center for Lasers and Photonics, Indian Institute of Technology Kanpur, Kanpur 208016, IndiaOver the past decade, scientists have learned how to manipulate the interaction of radiation withstructured materials to an unprecedented level. For decades, our world was limited to materialswith primarily positive permittivities and permeabilities, with a few exceptions such as plasmas,for example, whose permittivities can be negative. The research in metamaterials coupled withthe rapid advancements in micro- and nanofabrication technologies has removed this limitationand has opened the door to almost arbitrary material properties with some extraordinary con-sequences across the electromagnetic spectrum, ranging from radio frequencies to opticalfrequencies. These developments have been strongly complemented by the developments inperiodic dielectric photonic crystals where band-gap effects lead to mind-blowing dispersioncharacteristics and consequent effects. Almost simultaneously, the optics of metals has beenbrought to center-stage where the plasmonic excitations enable the electromagnetic radiationto interact resonantly with the structured material at very small sub-wavelength scales.These interactions prove to be the key to manipulating the optical near-field, and surprisingeffects such as sub-wavelength scale imaging by so-called super-lenses made of negative refrac-tive index or plasmonic materials have been discovered.AfocuseddiscussionmeetingonMetamaterialsandPhotonicNanostructureswasheldatIITKanpur on 16–17 August 2013 to bring researchers working on these topics to a common plat-form and to enable an interactive period for knowledge pooling. One of the intents was to takestock of theworkcarriedout in India in these frontier areas, and most of the activeresearchers inIndia contributed to the meeting. This special section consists of selected papers based on workpresented at the meeting, as well as papers contributed in response to the call for this specialsection.The special section has attracted an interesting collection of works ranging from surfaceenhanced Raman scattering from nanostructured plasmonic systems, interactions between local-ized and propagating surface plasmons in subwavelength gratings, extraordinary transmission instructured plasmonic thin films, anisotropic uniaxial metamaterials and epsilon-zero metamate-rials, fabrication techniques for embedding nondiffracting defect sites, large area nanophotonicstructures and inorganic-organic layered perovskites, to theoretical treatments of third harmonicgeneration in photonic crystals and super-continuum generation in microstructured opticalfibers. The large variety of the topics is reflective of the ever-increasing appeal and applicationsof metamaterials and nanostructured materials across optics.

The “submarine hatch” nail bed biopsy

From the Department of Dermatology, Herbert Wertheim College of Medicine, Florida International University; Greater Miami Skin and Laser Center, Mount Sinai Medical Center; and the Department of Dermatology and Cutaneous Surgery, University of Miami Miller School of Medicine. Funding sources: None. Conflicts of interest: None declared. Reprint requests: Martin N. Zaiac, MD, Greater Miami Skin and Laser Center, 4308 Alton Rd, Ste 750, Miami Beach, FL 33140. J Am Acad Dermatol 2014;70:e127-8. 0190-9622/$36.0

Endoluminal tracheal stenting prior to head and neck PDT

Head and Neck Unit, University College London Hospital NHS Trust, London, UK Department of Oral and Maxillofacial Surgery, UCL Eastman Dental Institute, London, UK Department of Oral and Maxillofacial Surgery, College of Dentistry, University of Mosul, Mosul, Iraq Division of Surgery and Interventional Science, National Medical Laser Centre, UCL Medical School, ondon, UK vailable online 2 May 2014

-switched and mode-locked -doped fibre laser using a single-multi-single fibre filter and piezoelectric

The active -switched and passive mode-locked -doped all-fibre laser is presented. The fibre laser centre wavelength is located at and determined by the homemade single-multi-single (SMS) in-line fibre filter. The laser spectrum width is nearly . The active -switched mechanism relies on the polarisation state control using a piezoelectric to press a segment of passive fibre on the circular cavity. The nonlinear polarisation rotation technology is used to realise the passive self-started mode-locked operation. In the passive mode-locked regimes, the output average power is , repetition frequency is , and single pulse energy is . With the -switched regimes running, the output average power is . The total -switched pulse width is , and every -switched pulse is made up by several tens of mode-locked peak pulses. The calculated output pulse energy of the -switched fibre laser is about , and the energy of every mode-locked pulse is about during a -switched pulse taking into account the power fraction propagating between pulses.

Laser therapy and photosensitive medication: a review of the evidence

In the 2009 guidelines from the BMLA, the use of non-essential aesthetic lasers was contraindicated in patients receiving medication that causes whole-body photosensitisation as well as those causing local light sensitisation. Following this and anecdotal advice, many laser centres refuse to treat patients who are on known photosensitive medication. Therefore, specific patient cohorts that would benefit from laser therapy are being denied because of medications, such as long-term antibiotics for chronic facial acne. This article reviews the published literature on lasers and photosensitive medications, the mechanisms of photosensitivity and the role of laser in its production. The aim is to analyse the available evidence regarding adverse reactions to laser treatment related to photosensitive medication. A PubMed review of published article titles and abstracts was performed using the search term Laser with each of the following terms individually: photosensitive, photosensitiser, photosensitizer, phototoxicity, photoallergy, complications, case-report, tetracycline, minocycline, amiodarone, nitrofurantoin and medication. Four publications were identified, none of which reported any complication in the use of laser in patients taking photosensitising medication. As there are no published accounts of adverse effects of laser in patients with photosensitive medication, we performed a review of the mechanism of photosensitivity by compiling a list of photosensitive medication and the peak wavelength of radiation required to activate the drug. We recommend a national database of drugs and the wavelengths causing photosensitive reactions of each which a laser department can access prior to treatment.

Reply

We note the comments made by Moise and colleagues regarding our study, ‘Fetoscopic laser ablation of placental anastomoses in twin–twin transfusion syndrome using ‘Solomon technique’, published in this journal last year1, and welcome the opportunity to provide further information about our study. Moise et al. stated that their esteemed colleagues at Leiden University (Enrico Lopriore et al.) described the Solomon method 3 years earlier than did Chalouhi et al.. We would like to point out that there was never a claim of primacy regarding the Chalouhi et al. study2 made in our article. Enrico Lopriore et al.3 may well have been the first to use the term. Moise et al. make the statement that: ‘Most laser centers in such large countries as the USA and Brazil serve a large referral population base with great geographic distribution. As such, complete perinatal follow-up is difficult.’ While we cannot make sweeping statements about the type of follow-up offered by their center or that offered by ‘most laser centers in large countries’, we do pride ourselves on our own efforts to obtain this information for our patients, regardless of their geographic origin. While it may be difficult, it can certainly be done, and we follow all our post-laser patients closely with Doppler studies after surgery, in some cases performed by the referring physicians, and in others (more local) by ourselves. In the patients involved in our study none was lost to follow-up. As requested, in Table 1, we have provided further information about the six cases that developed twin anemia-polycythemia sequence (TAPS). The ‘Solomon technique’ was not performed in any of these patients. As demonstrated in Table 1, all had Doppler studies confirming the diagnosis of TAPS4. Three of these patients had an anterior placenta and three had a posterior placenta. Intrauterine fetal blood transfusion was performed in one case (Case 1). In four of the six cases, the TAPS was diagnosed late and all four were delivered by preterm Cesarean section. One patient had twin demise in utero and the classic features of anemia and plethora were confirmed at delivery but no hemoglobin values could be obtained. The remaining five twin sets had postnatal confirmation of an intertwin hemoglobin difference > than 8 g/dL. Regarding the number of ‘unsuccessful’ cases of complete ‘Solomonization’, we did not receive all of the placentae for pathological examination and so cannot be sure. This was, unfortunately, one of the limitations of our study. Moise et al. stated that: ‘The dual neonatal survival rate in the control group was 46%, a rate that is lower than that reported by other experienced centers’. We note that Moise and his colleagues have not supplied us with their dual fetal survival prior to their adoption of the Solomon technique, but we are reasonably sure that it was very similar to that reported in our paper, and that reported by another USA center (50.7%)5. The surgeons who operated on the cases in our study were experienced and were not new to laser surgery6. Thus, we feel that the improvement in dual survival that we, and others7, have shown following adoption of the Solomon technique is most probably due to the benefits of the technique itself, and not due to increasing experience of the operators. In fact, the results of one of our trainees, who learned to perform laser therapy using only the Solomon technique, show dual survival of 70% (14/20) for his first 20 cases (pers. comm.), which suggests that good results are possible even during the learning curve using this technique. His cases were all performed after July 2012. This result compares favorably with that reported by the experienced operators in Moise's group (75%)8. Given that our study was not a randomized controlled trial, and that the two techniques were employed sequentially in our study, the question is still valid, and is one that, hopefully, will be answered soon by the randomized controlled trial that is underway. R. Ruano*†, C. Rodo‡, J. L. Peiro‡, A. A. Shamshirsaz†, S. Haeri†, M. L. Nomura§, E. M. A. Salustiano§, K. K. De Andrade§, H. Sangi-Haghpeykar†, E. Carreras‡ and M. A. Belfort† †Baylor College of Medicine and Texas Children's Hospital, Department of Obstetrics and Gynecology, Division of Maternal-Fetal Medicine, Houston, TX, USA; ‡Hospital Universitari Vall d'Hebron and University Autonoma de Barcelona, Fetal Surgery Program, Barcelona, Spain; §Maternal-Fetal Institute in Campinas, Campinas, Brazil *Correspondence. Pavilion for Women – Texas Children's Fetal Center, 6651 Main Street, Suite F1020, Houston, TX 77030, USA (e-mail: ruano@bcm.edu; rodrigoruano@hotmail.com)

Variation in the time length for the occurrence of Posterior Capsular Opacification following PMMA versus AcrySof Intraocular lens implants

Aim: To evaluate the significance of the biomaterial composition of the implanted Intra Ocular Lenses, in the occurrence of Posterior Capsular Opacification following a cataract surgery. Methods: A total of 75 patients who underwent IOL implant surgery were studied. The patients were classified based on the biomaterial of the IOL implanted in the eye following a cataract surgery. Group A consisted of eyes implanted with Polymethyl Methacrylate IOLs and Group B consisted of eyes implanted with AcrySof IOLs. The patients were later treated with YAG laser to clear the Posterior Capsular Opacification at the Ujjain laser center, Ujjain, Madhyapradesh. Results: The incidence of Posterior Capsular Opacification was found to develop earlier in the eyes implanted with PMMA IOLs as compared to Posterior Capsular Opacification occurrence in eyes implanted with AcrySof IOLs. Conclusion: The incidence of Posterior Capsular Opacification was found to be delayed by the use of AcrySof IOLs when compared to the use of PMMA IOLs. Index terms:Intraocular lenses, Polymethyl Methacrylate, AcrySof, Posterior Capsular Opacification, Lens epithelial cells, Capsulotomy, Biocompatibility I. Introduction The occurrence of Posterior Capsular Opacification is a prominent complication observed postoperatively in patients implanted with IOLs following a cataract surgery. The surgery involves removal of the anterior capsular bag, leaving the posterior capsular bag and the anterior capsular edge. Thereafter the lens nucleus and cortex is removed via phacoemulsification, small incision cataract surgery or any other standardized method. The surgery leaves the capsular bag with traces of Lens Epithelial Cells and fibers. The leftover Lens epithelial cells proliferate, undergo abnormal differentiation and migrate from the equator to the center, causing visual axis obscuration and dimness in vision. The factors that play a role in Posterior Capsular Opacification include biomaterial of the IOL, the edge of the IOL and the surgical skills of the surgeon. This study presents a comparison in the significance of the biomaterial of the IOLs and the shape of the IOLs, in the time length variation for the occurrence of Posterior Capsular Opacification following a cataract surgery. All the surgeries that have been used for this study were performed by the same surgeon thus eliminating any errors that can be caused by differences in surgical skills. Posterior Capsular Opacification can be treated by posterior capsule scrapping, which is a surgical method or by Nd: YAG laser capsulotomy, which is a non-surgical method. Under various studies, AcrySof IOLs have been found to have very low incidence of Posterior Capsular Opacification when compared to Posterior Capsular Opacification incidence in PMMA IOLs. This reduced incidence of Posterior Capsular Opacification in AcrySof IOLs is due to lower migration of lens epithelial cells (LECs) on the posterior capsule and their subsequent regression (1). AcrySof lenses have presented no signs of regeneration of Posterior Capsular Opacification after the capsulotomy via Nd:YAG laser. The following paper represents a comparative study of the occurrence of Posterior Capsular Opacification following PMMA vs AcrySof IOL implantation.

Engineering-reflected phase in Fabry–Perot sensors with resonant mirrors

Fabry-Perot cavities made with photonic crystal (PC) mirrors and other resonant structures exhibit nontraditional characteristics due to the strong wavelength dependence of their reflected phase. This Letter describes how engineering the phase of PC mirrors enables sensors that are tolerant to variations in laser center frequency and line width. Reflection spectra measurements of Fabry-Perot cavities made with PC mirrors were collected as a function of wavelength and cavity length, providing experimental verification of theory and simulations.

Clinical efficacy of the 595 nm pulsed dye laser in the treatment of childhood superficial hemangioma – analysis of 10-year application in Chinese patients

Background: The 595 nm tunable pulsed dye laser has been used in China for more than 10 years. However, no studies about its effect and side-effect in treatment of superficial hemangioma have been documented. Objective: This study was designed to retrospectively summarize its usage in Chinese patients. Methods: Infant patients with superficial hemangioma, who had received 595 nm tunable pulsed dye laser treatment in our laser center in the last 10 years, were recruited. Detailed demographics, results of assessment about their degree of clearance and clinical examination for treatment complications were entered into SASS10.0 version database, and statistical analyses were conducted. Results: Six hundred and fifty-seven cases with superficial hemangioma were recruited. The overall effectiveness rate was 91.17%. Female patients respond better than male, the difference was statistically significant (p < 0.001). Lesions at different part of the body respond differently to the treatment with lesions on extremities show the best result. The response rate does not increase with time of treatments. The most common side-effects were pigment changes and skin atrophy, which usually resolve spontaneously and disappear completely in a few months. Conclusions: Our experience confirmed the satisfactory clinical efficacy and safety of the 595 nm tunable pulse dye laser in the treatment of childhood superficial hemangioma.

The diverse application of laser hair removal therapy: a tertiary laser unit's experience with less common indications and a literature overview

We describe the diversity of indications for laser hair removal (LHR) therapy and compare our experience with the literature. Patients' case notes referred to the Birmingham Regional Skin Laser Centre between 2003 and 2011 for laser hair removal, with indications other than hirsutism, were reviewed retrospectively. Thirty-one treated patients with the following indications were identified: hair-bearing skin grafts/flaps, intra-oral hair-bearing flap, Becker's naevus, localised nevoid hypertrichosis, peristomal hair-bearing skin, scrotal skin prior to vaginoplasty in male-to-female (MTF) gender reassignment, pilonidal sinus disease (PSD), pseudofolliculitis barbae (PFB) and hidradenitis suppurativa (HS). Seven patients with the following indications have been reported before: intra-oral hair-bearing graft, naevoid hypertrichosis and peristomal hair-bearing skin. A clinical review of the evidence available for each indication is provided. Our experience and that in the published literature suggest that LHR is a safe, well-tolerated and effective treatment modality for the indications we report, leading to significant symptom and functional improvement with high patient satisfaction. LHR appears effective in the treatment of chronic inflammatory conditions such as PSD, PFB and HS, particularly at an early disease stage. We aim to increase awareness of the diversity of laser hair removal indications and add evidence to the medical literature of the wide range of indications for this useful treatment modality.

Pulsed-Laser Time-Resolved Thermal Mirror Technique in Low-Absorbance Homogeneous Linear Elastic Materials

A theoretical model for a time-resolved photothermal mirror technique using pulsed-laser excitation was developed for low absorption samples. Analytical solutions to the temperature and thermoelastic deformation equations are found for three characteristic pulse profiles and are compared to finite element analysis methods results for finite samples. An analytical expression for the intensity of the center of a continuous probe laser at the detector plane is derived using the Fresnel diffraction theory, which allows modeling of experimental results. Experiments are performed in optical glasses, and the models are fitted to the data. The parameters of the fit are in good agreement with previous literature data for absorption, thermal diffusion, and thermal expansion of the materials tested. The combined modeling and experimental techniques are shown to be useful for quantitative determination of the physical properties of low absorption homogeneous linear elastic material samples.

Uncertainty Estimation for Performance Evaluation of a Confocal Microscope as Metrology Equipment

Both in industry and research, the quality control of micrometric manufactured parts is based on the measurement of parameters whose traceability is sometimes difficult to guarantee. In some of these parts, the confocal microscopy shows great aptitudes to characterize a measurand qualitatively and quantitatively. The confocal microscopy allows the acquisition of 2D and 3D images that are easily manipulated. Nowadays, this equipment is manufactured by many different brands, each of them claiming a resolution probably not in accord to their real performance. The Laser Center (Technical University of Madrid) has a confocal microscope to verify the dimensions of the micro mechanizing in their own research projects. The present study pretends to confirm that the magnitudes obtained are true and reliable. To achieve this, a methodology for confocal microscope calibration is proposed, as well as an experimental phase for dimensionally valuing the equipment by 4 different standard positions, with its seven magnifications and the six objective lenses that the equipment currently has, in the x–y and z axis. From the results the uncertainty will be estimated along with an effect analysis of the different magnifications in each of the objective lenses.

EPR study of the effect of ionizing radiation on chromium centers in Mg2SiO4: Cr,Li laser crystals

Forsterite single crystals doped with chromium and lithium and exposed to ionizing radiation have been studied using multifrequency electron paramagnetic resonance (EPR) spectroscopy. It has been found that ionizing irradiation up to a dose of 108 rad does not lead to a significant change in the concentration of single chromium impurity centers. At the same time, γ-ray irradiation of the crystal leads to a decrease in the concentration of active laser centers, which form an associate of trivalent chromium and monovalent lithium in the crystallographic positions M2 and M1, respectively, and to the formation of new centers of divalent chromium. The structure and magnetic properties of the new centers have been discussed.