Multiparameter bifurcations and mixed-mode oscillations in Q-switched CO2 lasers

We study the origin of mixed-mode oscillations and related bifurcations in a fully molecular laser model that describes CO2 monomode lasers with a slow saturable absorber. Our study indicates that the presence of isolas of periodic mixed-mode oscillations, as the pump parameter and the cavity-frequency detuning change, is inherent to Q-switched CO2 monomode lasers. We compare this model, known as the dual four-level model, to the more conventional 3:2 model and to a CO2 laser model for fast saturable absorbers. In these models, we find similarities as well as qualitative differences, such as the different nature of the homoclinic tangency to a relevant unstable periodic orbit, where the Gavrilov-Shilnikov theory and its extensions may hold. We also show that there are isolas of periodic mixed-mode oscillations in a model for CO2 lasers with modulated losses, as the pump parameter varies. The coarse-grained bifurcation diagrams of the periodic mixed-mode oscillations in these models suggest that these oscillations belong to similar classes.

Bistability and hysteresis in an optically injected two-section semiconductor laser

The effect of coherent single frequency injection on two-section semiconductor lasers is studied numerically using a model based on a set of delay differential equations. The existence of bistability between different continuous-wave and nonstationary regimes of operation is demonstrated in the case of sufficiently large linewidth enhancement factors.

A preliminary study on the safety and efficacy of a novel fractional CO₂ laser with synchronous radiofrequency delivery

Building upon the fractional CO₂ technology incorporated into the first generation SmartXide DOT (DEKA / ElEn, SpA, Calenzano, Italy) introduced in the U.S. in 2008, a second generation SmartXide Quadro has recently been introduced. This is a versatile device that has the ability to combine fractional CO₂ laser output for skin resurfacing with the synchronous delivery of bipolar radiofrequency (RF) energy for deeper, more diffuse heating. A pilot study was undertaken to demonstrate the safety and efficacy of the SmartXide Quadro, employing both fractional CO₂ laser output combined with the synchronous delivery of radiofrequency energy for the treatment of facial rhytides and acne scars. Ten patients, all women, six with facial rhytides and four with acne scarring, were treated with the SmartXide Quadro, a variably pulsed CO₂ laser with Pulse Shape Design® technology, a microablative DOT scanner and synchronized bipolar RF emission. Each patient was treated with a single fractional CO₂ laser-RF treatment; laser and RF parameters varied according to the severity of the rhytides or acne scars and were based upon both manufacturer-recommended settings and surgeon experience. Follow-up was at three days, one week, 2 weeks, and one month, three months, and six months after treatment. Results were judged by comparison of preoperative and post-operative photos evaluated by independent physicians, preoperative and post-operative grading by treating physicians, subjective evaluation of results by the patients themselves, and tabulation and categorization of adverse events (AEs). The SmartXide Quadro variably pulsed CO₂ laser with a microablative DOT scanner, with synchronous delivery of bipolar RF energy emission, proved to be both safe and effective in the treatment of facial rhytides and acne scars. The single treatment protocol was well tolerated and recovery was similar to fractional CO₂ laser skin resurfacing alone. The AEs were minimal and no significant complications occurred.

Diabetic retinopathy treated with laser photocoagulation and the indirect effect on glycaemic control

PURPOSE

To identify any possible relation between glycaemic control and previous laser photocoagulation for diabetic retinopathy.

METHODS

Seventy-two patients with diabetes were included in the study and were separated into 2 groups according to previous treatment (group A) or not (group B) with argon laser photocoagulation. Glycaemic control was estimated by measuring blood levels of HbA1c in four consecutive measurements.

RESULTS

Blood levels of HbA1c in group A were significantly lower 3, 6, and 12 months after laser treatment as compared to blood levels of HbA1c before laser treatment (7.1 ± 0.4% versus 7.6 ± 0.9%, 7.2 ± 0.2% versus 7.6 ± 0.9%, and 7.1 ± 0.2% versus 7.6 ± 0.9%, resp., all P < 0.05). Blood levels of HbA1c in group B did not differ significantly in four consecutive measurements.

CONCLUSION

Our results suggest that we should anticipate a better glycaemic control in cases of patients with diabetes previously treated with laser photocoagulation.

CO₂-lased enamel microhardness after brushing and cariogenic challenge

This study aimed to assess how the wear that brushing promotes affects CO₂ laser-irradiated enamel microhardness after cariogenic challenge in vitro. Forty fragments measuring 4 × 4 mm were randomly assigned to four groups according to the enamel surface treatment: G1-control, G2-CO₂-laser irradiation, G3-brushing, and G4-CO₂ laser irradiation + brushing. A laser device emitting at 10.6 μm was used (power=0.5 W, energy per pulse=0.05 mJ, and frequency=10 kHz). Specimens belonging to groups G3 and G4 were brushed (80,000 strokes) with a brushing simulator using toothpaste. Next, the samples were challenged with acid: the specimens were immersed in demineralizing and remineralizing solutions for 8 days. The acid resistance of enamel was evaluated by cross-sectional microhardness tests. The area under the curve (KHN × μm) was calculated. Analysis of variance (ANOVA) one-away and Fisher's test were performed for the statistical analysis (p<0.05). Group G2 specimens (31,185 ± 4706) were statistically different from specimens belonging to groups G1 (26,723 ± 2446), G3 (28,194 ± 1376), and G4 (28,207 ± 2234), which were statistically similar. The brushing time used in the present study probably wore the CO₂-lased enamel, so demineralization could not be prevented in the brushed group.

Lasers and photodynamic therapy in the treatment of onychomycosis: a review of the literature

Onychomycosis is a widespread problem. Oral antifungal medications are currently the gold standard of care, but treatment failure is common and oral therapy is contraindicated in many cases. There is a need for effective treatment without the systemic complications posed by oral therapy. Laser and photodynamic therapy may have the potential to treat onychomycosis locally without adverse systemic effects; some small studies have even reported achieving clinical and mycologic cure. However, there is reason for restraint; these therapies are expensive and time-consuming. Furthermore, they may not be covered by insurance and have not been proven effective with randomized, controlled clinical trials. This paper will review current literature regarding the use of laser and photodynamic therapy as potential treatments for onychomycosis.

Influence of laser light on bioimplants used in otorhinolaryngology

In otorhinolaryngology, dermatology and reconstructive surgery biomaterials as implants and a variety of lasers are used. Laser light applied near to an implant could have the risk to damage these materials. Therefore, their resistance exposed to laser light is of interest. A diode laser emitting at 940 nm and a CO2 laser were used to investigate its effects to the biomaterials Bioverit®, Medpor® and Palacos®, and in addition, an excised implant containing Medpor® and nasal turbinate tissue, excised and fixed in formalin. The macro- and microscopic changes of the material, temperature development during laser energy application in dependency to distance of fibre and material, time of exposure and applied power were investigated. Interaction of diode laser light with Bioverit® (0 mm distance, 360 s, 10 W, 3,600 J) resulted in minimal microscopic effects in direct contact of with the fibre. Using Medpor® (1 mm, 10s, 10 W, 100 J) resulted in melting and perforation. In the case of Palacos® (0.6 mm, 10s, 10 W, 100 J), melting occurred creating a flat excavation. The effect to Medpor® in nasal turbinate (1-2 mm, 10s, 10 W, 100 J) showed tissue denaturation and carbonisation and creation of a hole. The interaction of the CO2 laser with Bioverit® (3 cm, 0.5, 1 and 5 s, 2, 10 or 20 W) induced melting and discolouring resulting finally in a perforating hole. Depending on the material, first damage starts 10 s after an impact of 100 J (threshold value). So interaction between laser energy and biomaterials occurs. This should be carefully considered during clinical laser treatments especially nearby implants.

3D finite element model for writing long-period fiber gratings by CO2 laser radiation

In the last years, mid-infrared radiation emitted by CO₂ lasers has become increasing popular as a tool in the development of long-period fiber gratings. However, although the development and characterization of the resulting sensing devices have progressed quickly, further research is still necessary to consolidate functional models, especially regarding the interaction between laser radiation and the fiber's material. In this paper, a 3D finite element model is presented to simulate the interaction between laser radiation and an optical fiber and to determine the resulting refractive index change. Dependence with temperature of the main parameters of the optical fiber materials (with special focus on the absorption of incident laser radiation) is considered, as well as convection and radiation losses. Thermal and residual stress analyses are made for a standard single mode fiber, and experimental results are presented.

Topical lidocaine enhanced by laser pretreatment: a safe and effective method of analgesia for facial rejuvenation

BACKGROUND

Injectable forms of anesthesia for nonsurgical facial rejuvenation, although efficacious, are uncomfortable for the patient. Preclinical studies have demonstrated that laser pretreatment at low energies enhances absorption of topical lidocaine.

OBJECTIVES

The authors assess the safety and efficacy of laser-assisted transdermal delivery of topical anesthetic.

METHOD

Ten patients were split into 2 groups (A and B). All patients received 15 g of BLT (20% benzocaine, 6% lidocaine, and 4% tetracaine triple anesthetic cream) for 20 minutes with no occlusion. Then the cream was removed and the first blood draw taken. Group A patients were pretreated with the full ablative laser and group B patients with a fractional ablative laser to the full face. A further 15 g BLT was applied for another 20 minutes. Group A patients then underwent full ablative laser treatment, and group B received fractionated ablative laser treatment. Blood draws were taken at 60, 90, 120, 180, and 240 minutes after the initial topical anesthetic application, and the serum was analyzed for lidocaine and monoethylglycinexylidide (MEGX) levels. Patients were asked to rate the pain felt at intervals during the procedure.

RESULTS

No patient required supplemental nerve blocks. Pain scores were equivalent at the end of the first pass for both groups (P = .436). Group A patients had significantly lower pain scores at the start of the second laser treatment (P = .045), but pain scores became equivalent by the end (P = .323). Combined serum lidocaine and MEGX levels were significantly higher in group A patients up to 90 minutes (peak average of 0.61 µg/mL for group A and 0.533 µg/mL for group B; P = .0253), which corresponded to greater initial analgesic effect.

CONCLUSIONS

Data from this study demonstrate that topical anesthetic for facial rejuvenation can be enhanced with laser pretreatment while maintaining safe blood serum levels. Further studies should examine optimal application amount and time to allow safe multipass facial rejuvenation without the need for invasive nerve blocks.

Use of light-curing units in orthodontics

Because of their wide field of applications, light-curing units are now indispensable for orthodontists and general dentists; thus, it is important to be familiar with the various types of light-curing units, their history, specifications, advantages, and disadvantages. For this review, a search of the PubMed database (from 1966 to March 2010) was conducted using the search term "curing lights orthodontics". Eligibility of the selected studies was determined by reading the abstracts of articles identified by the search. All the articles that met the inclusion criteria were selected, and the articles collected. The reference lists of the retrieved articles were also hand searched for any applicable studies that might have been missed in the database searches. When selecting curing lights for an office, many variables need to be considered. Armed with knowledge about each curing-light category, orthodontists can evaluate their unique practice style and select the appropriate light/lights.

Temperature control of water-based substances by CO2 laser for medical applications

Temperature of water-based substances is investigated by aiming a pulsed CO(2) laser beam at the water-air surface. This method of controlling temperature is believed to be flexible in medical applications as it avoids the use of thermal devices, which are often cumbersome and generate rather larger temperature swing with time. The control of temperature in this laser method is modeled by the heat conduction equation. In this investigation, it is assumed that the energy delivered by the CO(2) laser is confined within a very thin surface layer of roughly 10 μm. It is shown that the temperature can be very well controlled by a CO(2) laser at a steady temperature, and we demonstrate that the method can be adapted to work in tandem with another laser beam.

Comparison of modified driver circuit and capacitor-transfer circuit in longitudinally excited N2 laser

We developed a modified driver circuit composed of a capacitance and a spark gap, called a direct-drive circuit, for a longitudinally excited gas laser. The direct-drive circuit uses a large discharge impedance caused by a long discharge length of the longitudinal excitation scheme and eliminates the buffer capacitance used in the traditional capacitor-transfer circuit. We compared the direct-drive circuit and the capacitor-transfer circuit in a longitudinally excited N2 laser (wavelength: 337 nm). Producing high output energy with the capacitor-transfer circuit requires a large storage capacitance and a discharge tube with optimum dimensions (an inner diameter of 4 mm and a length of 10 cm in this work); in contrast, the direct-drive circuit requires a high breakdown voltage, achieved with a small storage capacitance and a large discharge tube. Additionally, for the same input energy of 792 mJ, the maximum output energy of the capacitor-transfer circuit was 174.2 μJ, and that of the direct-drive circuit was 344.7 μJ.

Combined fractional ablative and nonablative laser resurfacing treatment: a split-face comparative study

BACKGROUND

Fractional ablative and nonablative lasers are useful tools for facial rejuvenation; however, ablative lasers require a period of downtime during reepthelialization. A procedure that combines both ablative and nonablative lasers may deliver good cosmetic results and reduce downtime or other side effects of treatment.

OBJECTIVE

The purpose of this study was to compare a combined fractional ablative and nonablative laser procedure to ablative-only procedures for facial rejuvenation.

METHODS

A total of 8 subjects in 2 study groups received a single, split-face, facial rejuvenation procedure in this study. In group A, we compared a combined procedure using a fractional nonablative 1,440-nm neodymium-doped yttrium aluminum garnet (YAG) laser and a fractional ablative 2,940-nm erbium (Er)-doped YAG laser on one side of the face, and a combined confluent/fractional ablative Er:YAG laser on the other. In group B, we compared the same 1,440/2,940 treatment as group A on one side of the face, and a fractional ablative CO2 laser on the other. Subjects were followed for 3 months to assess side effects and improvement in Fitzpatrick Wrinkle Score and pigmentation.

RESULTS

Improvement in wrinkles and pigment were seen with all techniques in both groups, and results were equivalent. Areas treated with combined fractional nonablative and ablative technique demonstrated fewer immediate side effects.

CONCLUSION

Facial rejuvenation using a combination treatment of fractional ablative 2,940 and nonablative 1,440 lasers provides improvement in wrinkles and pigment similar to conservative purely ablative approaches. These purely ablative approaches include the Er:YAG laser used in a sequential confluent fractional manner, or fractional CO2 laser alone. Reduced side effects make the combined procedure an attractive option for facial rejuvenation.

[Age peculiarities of the muscle regeneration after injury, exposure to he-ne laser and alloplasty with muscle tissue from the animal of the same age]

The recovery of the injured muscles were studied in young (aged 1 month), adult (aged 3-4 months) and old (aged 24-30 months) outbred male rats (24 animals in each group) after alloplasty of the injured area with the muscle tissue taken from the animal of the same age under the conditions of implantation of muscle tissue, non-irradiated by laser, into the area of injury of the muscle irradiated by laser (1st series) and vice versa, implantation of the muscle tissue irradiated by laser, into the area of injured non-irradiated muscle (2nd series). It is shown that in each age group in the 1st and the 2nd series, the allogeneic muscle tissue is is capable of regeneration. The regenerate mass s and the proportion of muscle tissue in them tended to be greater in the animals in the 1-series, as compared to those in the 2nd series. Alloplasty with the muscle tissue of the animal of the same age was more effective in young rats than in the old ones.

The effect of vibration frequency and amplitude on biofouling deterrence

The use of vibration is proposed as a means of controlling the settlement of marine fouling organisms. In this study, panels with embedded lead zirconate titanate, known as PZT, were placed in the field over 3 months. The panels were vibrated at different velocity levels at frequencies between 70 and 445 Hz. It was found that barnacles (Amphibalanus variegatus Darwin and Elminius sp.) were the only fouling organisms affected by the applied vibration, and these organisms settled in significantly lower numbers when the plates were excited at specific frequencies and amplitudes. Panels vibrating at relatively higher frequencies, greater than 260 Hz, exhibited reduced barnacle settlement, whilst lower frequencies in the 70-100 Hz range had little or no effect. The settlement of other fouling organisms such as tubeworms, bryozoans, ascidians and algae did not appear to be affected by the applied excitation. The experimental results showed that increasing the velocity amplitude of vibration was a contributing factor in inhibiting barnacle settlement.

Fractional laser-assisted delivery of methyl aminolevulinate: Impact of laser channel depth and incubation time

BACKGROUND AND OBJECTIVES

Pretreatment of skin with ablative fractional lasers (AFXL) enhances the uptake of topical photosensitizers used in photodynamic therapy (PDT). Distribution of photosensitizer into skin layers may depend on depth of laser channels and incubation time. This study evaluates whether depth of intradermal laser channels and incubation time may affect AFXL-assisted delivery of methyl aminolevulinate (MAL).

MATERIALS AND METHODS

Yorkshire swine were treated with CO2 AFXL at energy levels of 37, 190, and 380 mJ/laser channel and subsequent application of MAL cream (Metvix) for 30, 60, 120, and 180 minutes incubation time. Fluorescence photography and fluorescence microscopy quantified MAL-induced porphyrin fluorescence (PpIX) at the skin surface and at five specific skin depths (120, 500, 1,000, 1,500, and 1,800 µm).

RESULTS

Laser channels penetrated into superficial (∼300 µm), mid (∼1,400 µm), and deep dermis/upper subcutaneous fat layer (∼2,100 µm). Similar fluorescence intensities were induced at the skin surface and throughout skin layers independent of laser channel depth (180 minutes; P < 0.19). AFXL accelerated PpIX fluorescence from skin surface to deep dermis. After laser exposure and 60 minutes MAL incubation, surface fluorescence was significantly higher compared to intact, not laser-exposed skin at 180 minutes (AFXL-MAL 60 minutes vs. MAL 180 minutes, 69.16 a.u. vs. 23.49 a.u.; P < 0.01). Through all skin layers (120-1,800 µm), laser exposure and 120 minutes MAL incubation induced significantly higher fluorescence intensities in HF and dermis than non-laser exposed sites at 180 minutes (1,800 µm, AFXL-MAL 120 minutes vs. MAL 180 minutes, HF 14.76 a.u. vs. 6.69 a.u. and dermis 6.98 a.u. vs. 5.87 a.u.; P < 0.01).

CONCLUSIONS

AFXL pretreatment accelerates PpIX accumulation, but intradermal depth of laser channels does not affect porphyrin accumulation. Further studies are required to examine these findings in clinical trials.

Position measurement of non-integer OAM beams with structurally invariant propagation

We present a design to generate structurally propagation invariant light beams carrying non-integer orbital angular momentum (OAM) using Hermite-Laguerre-Gaussian (HLG) modes. Different from previous techniques, the symmetry axes of our beams are fixed when varying the OAM; this simplifies the calibration technique for beam positional measurement using a quadrant detector. We have also demonstrated analytically and experimentally that both the OAM value and the HLG mode orientation play an important role in the quadrant detector response. The assumption that a quadrant detector is most sensitive at the beam center does not always hold for anisotropic beam profiles, such as HLG beams.

SNAP: fabrication of long coupled microresonator chains with sub-angstrom precision

Based on the recently-introduced Surface Nanoscale Axial Photonics (SNAP) platform, we demonstrate a chain of 30 coupled SNAP microresonators spaced by 50 micron along an optical fiber, which is fabricated with the precision of 0.7 angstrom and a standard deviation of 0.12 angstrom in effective microresonator radius. To the best of our knowledge, this result surpasses those achieved in other super-low-loss photonic technologies developed to date by two orders of magnitude. The chain exhibits bandgaps in both the discrete and continuous spectrum in excellent agreement with theory. The developed method enables robust fabrication of SNAP devices with sub-angstrom precision.

[Advancement in the research of fractional carbon dioxide laser in treating burn scars]

This paper reviews the new progress in the research of fractional carbon dioxide laser in treating hypertrophic scar after burn injury, which remains a challenging problem for burn care surgeons. There have been many traditional therapeutic approaches, such as compression remedy, operation, and so on. However, a satisfactory method is lacking to date. In recent years, the newly developed fractional carbon dioxide laser has been employed to treat different kinds of scars, and it has been proved to be effective in terms of an improvement of scar color, texture, and rigidity. It seems to be a promising method for scar treatment in future.

Antisepsis regimen in the surgical treatment of HPV generated cervical lesions: polyhexamethylene biguanide vs chlorhexidine. A randomized, double blind study

INTRODUCTION

To reduce the risk of local infections after surgical treatments for HPV infected cervical lesions, the post-operative regimen is generally based on the use of vaginal antimicrobial agents.

AIM

The efficacy and safety of polyhexamethylene biguanide-based vaginal suppositories was compared to a similar chlorhexidine-based treatment, in the post recovery regimen after surgical treatment of cervical lesions.

MATERIALS AND METHODS

50 women who underwent to CO2 laser therapy for cervical lesions were randomly assigned to receive 10 days of antiseptic treatment with chlorhexidine digluconate vaginal suppositories, or polyhexamethylene biguanide vaginal suppositories (Monogin®/Biguanelle® ovuli, Lo.Li. Pharma, Italy). A weekly follow-up check was performed for 6 weeks.

RESULTS

Polyhexamethylene biguanide-based treatment showed improved efficacy compared to chlorhexidine, in terms of healing process and prevention of bacterial infections.

CONCLUSIONS

Due to its safety and effectiveness, the vaginal treatment with polyhexamethylene biguanide is preferred to chlorexidine, in accordance with previously reported in vitro evidences.

Chirped laser dispersion spectroscopy for remote open-path trace-gas sensing

In this paper we present a prototype instrument for remote open-path detection of nitrous oxide. The sensor is based on a 4.53 μm quantum cascade laser and uses the chirped laser dispersion spectroscopy (CLaDS) technique for molecular concentration measurements. To the best of our knowledge this is the first demonstration of open-path laser-based trace-gas detection using a molecular dispersion measurement. The prototype sensor achieves a detection limit down to the single-ppbv level and exhibits excellent stability and robustness. The instrument characterization, field deployment performance, and the advantages of applying dispersion sensing to sensitive trace-gas detection in a remote open-path configuration are presented.