Short CO2 Laser Pulses Research Articles

Optimization of efficiency of short-pulsed fast flow CO2 laser amplifier with dual-band and multispectral lines

In this paper, we optimize the amplification efficiency of a nanosecond pulse CO2 laser in a fast flow amplifier using dual-band and multispectral lines techniques. Utilizing a six-temperature model and a random rotational relaxation model, we simulate the time-domain amplification process of dual-band and multispectral lines short-pulse seeds in a fast flow CO2 laser amplifier, analyzing the effects of input pulse fluence, pulse width, and spectral line composition on amplification efficiency. Compared to single-line 10P(20) amplification, the extraction efficiency of 10.6-µm and 9.6-µm dual-band two-line 15-ns pulses is improved by approximately 70%, surpassing that of 10.6-µm single-band four-line amplification. This study is of great significance for the efficient amplification of short-pulse CO2 lasers and the generation of extreme ultraviolet light from laser produced plasma.

Influence of pulse-tail energy of short-pulse CO2 laser in drilling of various glasses

In a short-pulse CO2 laser based on discharge excitation, there is a pulse tail that depends on the device configuration and operating conditions. The pulse tail is longer than the spike pulse and causes thermal effects such as a crack, heat-affected zones (HAZ), and so on. There are various types of glass having different physical constants related to heat, such as the thermal expansion coefficient and the softening point. Even if the same CO2 laser pulse is radiated onto glass, the processing results may differ depending on the glass material. Four types of glass, namely, crown glass, soda-lime glass, borosilicate glass, and synthetic quartz glass were irradiated with two types of short CO2 laser pulses, one with a large pulse tail and one with a small pulse tail, at a repetition rate of 200 Hz and a fluence per pulse of 22 J/cm2. As the processing characteristics, the ratios of the surface hole diameter and the HAZ diameter to the irradiation diameter, as well as the drilling depth, were investigated. The pulse-tail energy of the short CO2 laser pulses did not affect the surface hole diameter. In the glasses with small softening points of 740 °C or less, the pulse-tail energy of short CO2 laser pulses affected the HAZ with a large number of pulse irradiations with a total irradiation fluence of 2000 J/cm2 or more. The short CO2 laser pulses with a small tail produced a smaller HAZ than the short CO2 laser pulses with a large tail. In drilling with a large number of pulse irradiations, the short CO2 laser pulses with a small tail produced deeper drilling than the short CO2 laser pulses with a large tail. The glass material did not affect the surface hole diameter and the drilling depth. The glass material affected the HAZ.

Drilling of cylindrical holes in Crown glass by a short-pulse flat-top CO2 laser beam

We investigated cylindrical hole drilling in a crown glass with a high thermal expansion coefficient of 94 × 10–7 K−1 and a low melting point of 724 °C using a short-pulse CO2 laser with a flat-top beam, and also examined the drilling characteristics. The short laser pulse consisted of a pulse spike with a pulse width of 276 ns and a pulse tail with a length of 56.9 µs at a repetition rate of 200 Hz. The laser beam had a flat-top profile with an estimated M2 parameter of 13.5 and a diameter of 12.5 mm before a focusing lens. The flat-top beam was focused by the focusing lens, which had a focal length of 12.7 mm, on the glass surface at a focus offset of −0.20 mm to +0.40 mm. The incident flat-top beam produced conical holes at focus offsets of −0.20 mm to 0.00 mm and produced cylindrical holes at focus offsets of +0.20 mm to +0.40 mm. The hole depth of the cylindrical holes was 109 μm to 434 μm, the surface hole diameter was 150 μm to 366 μm, and the aspect ratio, defined as the ratio of the hole depth to the surface hole diameter, was 0.30 to 2.89. The hole depth was influenced by the focus offset and the total irradiation fluence, whereas the surface hole diameter, the taper angle and the ratio of the surface hole diameter to the irradiation diameter were influenced by the focus offset only. The ratio of the surface HAZ (Heat affected zone) diameter to the irradiation diameter was influenced by both the focus offset and the total irradiation fluence.

Application of short-pulsed CO2 laser and long-pulsed Nd:YAG laser in the treatment of severe hypertrophic port-wine stains

BackgroundThe treatment of port-wine stains (PWS) becomes extremely difficult due to age-related malformation of the vasculature. In this study, we used alternative methods to treat hypertrophic PWS. MethodsA short-pulsed CO2 laser was applied to ablate the hypertrophic vasculature of PWS. The ablation was ended when the wound was on the same plane as normal skin. The long-pulsed neodymium-doped yttrium-aluminum-garnet (lpNd:YAG) laser was primarily applied to coagulate and subsequently liquefy the hypertrophic vasculature of the PWS. The therapeutic energy used in treating different lesions should be carefully regulated to significantly affect the treatment outcomes. ResultsThe two cases presented herein demonstrated substantial improvement in hypertrophic vasculature that was largely removed. The skin was resurfaced, although some scar formation and mild hypopigmentation occurred. ConclusionWe suggest the use of short-pulsed CO2 and lpNd:YAG lasers for treating certain cases of hypertrophic PWS. When using a short-pulsed CO2 laser, it is wise to judge the treatment endpoint and take appropriate precautions to avoid intraoperative bleeding. When using an lpNd:YAG laser, the therapeutic energy should be controlled according to the thickness of the lesion to reduce scar formation.

1 kHz Oscillation of short-pulse CO2 laser pumped by longitudinal discharge without pre-ionization

Commonly, a gas laser pumped by a pulsed discharge requires a pre-ionization system to form a uniform discharge at a high repetition rate like 1 kHz. In this paper, however, a longitudinally excited CO2 laser without any pre-ionization system operated at a repetition rate of 1 kHz. The discharge tube was made of an alumina ceramic tube with an inner diameter of 8 mm, an outer diameter of 16 mm and a length of 80 cm, and two metallic electrodes attached to the two ends of the tube, and did not have a pre-ionization system or a fast gas flow system. The CO2 laser produced short pulses with a spike pulse width of 200 ns, a pulse tail length of 150 μs, a spike pulse to pulse tail energy ratio of 1:112, a laser energy of 35.2 mJ, and a circular Gaussian-like beam at a repetition rate of 1 kHz, a CO2/N2/He gas mixing ratio of 1:1:5, a gas pressure of 4.6 kPa and an input energy of 738 mJ to the circuit generating fast, high-voltage pulses. The dependence of the laser energy on the repetition rate, the CO2/N2/He gas mixing ratio, and the input energy was investigated.

Crown Glass Drilling by Short-Pulse CO2 Laser with Tunable Pulse Tail

Crown Glass Drilling by Short-Pulse CO2 Laser with Tunable Pulse Tail

Longitudinally excited short-pulse CO2 laser with large discharge tube without preionization

A longitudinally excited CO2 laser with a large discharge tube having an inner diameter of 16 mm and a length of 80 cm produced short laser pulses with an energy of 38.1 mJ at a repetition rate of 700 Hz. The CO2 laser did not have a preionization system or a fast gas flow system. The dependence of the laser output and discharge voltage on the repetition rate, the gas pressure and the structure of the discharge tube in 1:1:4 and 1:1:2 mixtures of CO2/N2/He gas was investigated. At a repetition rate of 300 Hz or more, the laser energy decreased as the repetition rate increased. The 1:1:4 mixture of CO2/N2/He gas produced a higher laser energy than the 1:1:2 mixture of CO2/N2/He gas. At a repetition rate of 300 Hz or less, the laser beam profile was doughnut-shaped. At a repetition rate of 400 Hz or more, the center of the laser profile had a high energy. At a high repetition rate, the fast discharge may have collected in the center of the discharge tube. Moreover, an increase in the repetition rate decreased the discharge formation time and the energy of a pulse tail part of the laser pulse waveform.

Shaping Optical Microresonators on the Surface of Optical Fibers With Negative Effective Radius Variations

We examine moderate CO2 laser heating as a method of forming negative effective radius variations in conventional optical fiber. Fiber samples were subjected to focused CO2 laser radiation in the form of 100 ms pulses with power 0.36 to 1.3 W and thermalization time up to 2.2 s. Fiber temperatures reached 200 to 300 degrees Celsius in each pulse. The temper atures are significantly smaller than the glass transformation temperature, which is nearly 1500 °C. We show that short CO2 laser pulses may introduce negative variations up to 5 nm. The magnitude of the introduced variation increases roughly linearly for up to 6 pulses, and then fiber saturation is achieved. We reveal that it is possible to produce optical whispering gallery modes resonators in low-temperature heating mode and create a triangular-shape microresonator solely with the negative variations. The negative variations may also occur in peripheral areas of high-temperature heated fiber while introducing positive effective radius variations. To eliminate it, we propose low-temperature fiber annealing before high-temperature variations introducing. The negative variations may also be implemented to develop a new independent approach of shaping optical whispering gallery modes microresonators.

Rapid CO2 laser processing technique for fabrication of micro-optics and micro-structures on fused silica materials

Micro-optics and micro-structures play important roles in the field of optics. A multi-step processing strategy with the combination of various processing technologies has been applied to fabricate micro-optics and micro-structures. However, the multi-step processing method is complex and expensive. In this work, a rapid CO2 laser processing technique is proposed to fabricate micro-optics and micro-structures on fused silica materials. First, high-power and short-pulse CO2 laser is used to achieve rapid prototyping of micro-optics and micro-structures with pre-designed geometry on fused silica. In this step, a maximum material removal rate of 1.53 mm3/min could be achieved with surface roughness better than 100 nm. Then, using the same CO2 laser source with reduced laser power density, the initially processed fused silica surface could be smoothed to improve the surface quality. By simulating the CO2 laser interaction with fused silica material, the formation mechanism of smooth surface is revealed, and the processing parameters for achieving smooth silica surface are proposed. The surface roughness of finally processed silica surface could reach 10.8 nm. Finally, as an application example of the processed two-step CO2 laser processing method, a micro-structure with special hexagonal shape on fused silica optics is successfully processed. The proposed rapid CO2 laser processing technique for the fabrication of micro-optics and micro-structures on fused silica materials can be realized with only one equipment, which can not only ensure the processing accuracy and efficiency but also reduce the processing cost.

In vitro CO2 9.3-μm short-pulsed laser caries prevention-effects of a newly developed laser irradiation pattern.

Caries prevention with different lasers has been investigated in laboratory studies and clinical pilot trials. Objective of this in vitro study was to assess whether 9.3-μm microsecond short-pulsed CO2 laser irradiation enhances enamel caries resistance without melting, with and without additional fluoride application. Seven groups of enamel, totaling 105 human enamel samples, were irradiated with 2 different carbon dioxide lasers with 2 different energy application systems (original versus spread beam; 9.3μm wavelength, pulse repetition rate 43Hz vs 100Hz, fluence ranges from 1.4 to 3.9J/cm2, pulse duration 3μs to 18μs). The laboratory pH-cycling was performed with or without additional fluoride, followed by cross-sectional microhardness testing. To assess caries inhibition, the mean relative mineral loss delta Z (∆Z) was determined. To evaluate for melting, scanning electron microscopy (SEM) examinations were performed. For the non-laser control groups with additional fluoride use, the relative mineral loss (ΔZ, vol% × μm) ranged between 512 ± 292 and 809 ± 297 (mean ± SD). ΔZ for the laser-irradiated samples with fluoride use ranged between 186 ± 214 and 374 ± 191, averaging a 58% ± 6% mineral loss reduction (ANOVA, P < 0.01 to P < 0.0001). For the non-laser-treated controls without additional fluoride, the mineral loss increased (ΔZ 914 ± 422 to 1224 ± 736). In contrast, the ΔZ for the laser-treated groups without additional fluoride ranged between 463 ± 190 and 594 ± 272 (P < 0.01 to P < 0.001) indicative of 50% ± 2% average reduction in mineral loss. Enhanced caries resistance was achieved by all applied fluences. Using the spread beam resulted in enhanced resistance without enamel melting as seen by SEM. CO2 9.3-μm short-pulsed laser irradiation with both laser beam configurations resulted in highly significant reduction in enamel mineral loss. Modifying the beam to a more homogenous profile will allow enamel caries resistance even without apparent enamel melting.

Toward little heat-affected area of fused silica materials using short pulse and high power CO2 laser

Abstract As a rapid and efficient processing technology, CO2 laser processing has been applied to remove fused silica materials. However, thermal effect caused by CO2 laser would lead to thermal modification layer, thermal deformation and residual stress in processed fused silica optics. To reduce the thermal effect, high power and short pulse CO2 laser is applied to remove the surface material of fused silica. In this work, a model coupling the physical processes of heat transfer and phase transition was established to simulate the complex interaction of CO2 laser with fused silica. Then, the model was applied to investigate the evolutions of temperature distribution and surface morphology involved in the laser ablating and melting processes. The results indicate that with the increase of laser power and decrease of pulse width, positive effect would take place that the radius-depth ratio of ablating area increases and the heat-affected area becomes smaller. For the application of CO2 laser with 0.2 μs pulse width and 800 kW peak power, fused silica material would quickly reach the ablation state. The ablation depth is less than 1 μm, and the thickness of heat-affected area is about 80 nm. It means that the high power and short pulse CO2 laser is equivalent to a hot grinding ball head, which can remove the material rapidly with small heat-affected area on fused silica surface. The simulation results of line scanning processing with CO2 laser were finally compared with the experiment ones, which verified the feasibility of the established model. The suggestions and prospective for improving the model were put forward as well.

Megafilaments in the mid-infrared

Focusing short CO2 laser pulses into air reveals rich ionization physics that is best explained by solid-state theories and results in centimetre-scale-diameter megafilaments that transport joules of energy.

Vagarious successful treatment of recalcitrant warts in combination with CO2 laser and imiquimod 5% cream

Background. Imiquimod 5% cream is widely regarded as a safe and effective option when treating recalcitrant warts, owing to the ointment's negligible side effects. However, our observations highlighted case of a patient incurring severe adverse reactions due to application of the cream, although the treatment proved successful in curing recalcitrant warts which had developed on the external auditory canal and external ear. Methods. All lesions were entirely removed with short-pulsed CO2 laser. As soon as the wound-healing process was completed, imiquimod 5% cream was self-applied on the healing wounds once daily for 5 days per week in a total of 2 weeks. Results. The patient appeared normal after the CO2 laser treatment and experienced severe redness, itching, exudation, and incrustation after a 2-week imiquimod 5% cream therapy. All lesions showed no recurrence during the 12-month followed-up process. Conclusions. We concluded that a feasible treatment modality to cure recalcitrant cutaneous warts is in combination of CO2 laser and imiquimod. Immunoenhancement plays an important role in the treatment of recalcitrant warts.

Optical Coherence Tomography Guided Laser Cochleostomy: Towards the Accuracy on Tens of Micrometer Scale

Lasers have been proven to be precise tools for bone ablation. Applying no mechanical stress to the patient, they are potentially very suitable for microsurgery on fragile structures such as the inner ear. However, it remains challenging to control the laser-bone ablation without injuring embedded soft tissue. In this work, we demonstrate a closed-loop control of a short-pulsed CO2 laser to perform laser cochleostomy under the monitoring of an optical coherence tomography (OCT) system. A foresighted detection of the bone-endosteum-perilymph boundary several hundred micrometers before its exposure has been realized. Position and duration of the laser pulses are planned based on the residual bone thickness distribution. OCT itself is also used as a highly accurate tracking system for motion compensation between the target area and the optics. During ex vivo experimental evaluation on fresh porcine cochleae, the ablation process terminated automatically when the thickness of the residual tissue layer uniformly reached a predefined value. The shape of the resulting channel bottom converged to the natural curvature of the endosteal layer without injuring the critical structure. Preliminary measurements in OCT scans indicated that the mean absolute accuracy of the shape approximation was only around 20 μm.

Successful treatment of congenital melanocytic nevus on tragus with CO2 laser

Background: Congenital melanocytic nevus (CMN) has an increasing risk of malignancy and may cause cosmetic and psychological problems. Surgery has been the main therapy for most cases. However, it is often not suitable for all lesions. Treatment of these lesions can be challenging to plastic surgeons. CO2 laser, with the special function, is another effective treatment for some CMN. Methods: Both lesions were treated with a short-pulsed CO2 laser in conjunction with a local anesthetic; the superfluous tissue was pruned and ablated to get a crude tragus and then carefully shaped to form an aesthetically tragus. Results: Showed good cosmetic results without pigment recurrence and scar formation 1 year after operation in both patients, the exception being a small area of cartilage that was covered with epithelial tissues on the surface in patient 1. Conclusions: CO2 laser treatment is a useful modality in treating some CMN that are located on sites deemed inoperable. It can help to shape the lesions into their original form with the advantage of hemostasis and tissue manipulation proving to be effective, thus avoiding suturing and skin grafting. Taking the thermal damage into account can help to minimize the side effects and attain a desirable cosmetic outcome.

Temporal and spatial temperature distribution in the glabrous skin of rats induced by short-pulse CO2 laser

Pain is a natural alarm that aids the body in avoiding potential danger and can also present as an important indicator in clinics. Infrared laser-evoked potentials can be used as an objective index to evaluate nociception. In animal studies, a short-pulse laser is crucial because it completes the stimulation before escape behavior. The objective of the present study was to obtain the temporal and spatial temperature distributions in the skin caused by the irradiation of a short-pulse laser. A fast speed infrared camera was used to measure the surface temperature caused by a CO2 laser of different durations (25 and 35 ms) and power. The measured results were subsequently implemented with a three-layer finite element model to predict the subsurface temperature. We found that stratum corneum was crucial in the modeling of fast temperature response, and escape behaviors correlated with predictions of temperature at subsurface. Results indicated that the onset latency and duration of activated nociceptors must be carefully considered when interpreting physiological responses evoked by infrared irradiation.

Scaling of high average power, short-pulse CO2 lasers

The scaling rule of high average power, short-pulse CO2 lasers is described based on the physical fundamentals. Specifications are required for lasers applied to high-volume manufacturing extreme-ultraviolet light sources, simultaneously on the average power over 10 kW, the beam quality less than 2 for M2, and the pulse width in the 10 ns range. The amplifier is operated by a cascade amplifier arrangement, and the ruling principle is approximately described by the Frantz-Nodvik equation, with effective small-signal gain g0 and saturation fluence Es depending on the amplifier medium and amplified pulse width. Thermal distortion is caused in the optical components, leading to beam propagation instability. The general rule of g0L<3, where L is the optical gain length, is the requirement to isolate each amplifier by optical shutters. Multiline amplification is efficient to increase the extraction efficiency in the case of less-efficient rotational relaxation. It is concluded that a well-designed single-beam, short-pulse CO2 laser is operable at 20 kW average output power based on available components, by satisfying all requirements.

Design of high brightness laser-Compton source for extreme ultraviolet and soft x-ray wavelengths

Design of a clean, high-brightness light source is presented for extreme ultraviolet/soft x-ray (EUV/SXR) lithography research and mask inspection. Basic characteristics of classical laser-Compton scattering are reviewed, and the laser and electron beam parameters at relatively low energy (EUV to SXR) photon generation are optimized. Recent achievements in each component technology are evaluated on a continuous wave (CW)-operated electron linac and energy recovery linac system, based on superconducting technologies at a 1.3 GHz operation frequency, 10 kW average power, short pulse CO2 laser, and optical super cavity with a 600- enhancement- factor at 10.6 μm wavelength. Combining both the CW electron beam and short pulse CO2 laser with super-cavity enhancement, 1 mW/2% ?startb.w.end? flux and 30 kW/mm2/sr/2% ?startb.w.end? brightness laser-Compton source is designed at 6.7-nm wavelength. The technological gap in the present component technologies are discussed, as well as any further required developments.

Simple Short-Pulse CO2 Laser Excited by Longitudinal Discharge without High-Voltage Switch

We have developed a longitudinally excited CO2 laser without a high-voltage switch. The laser produces a short laser pulse similar to those from TEA and Q-switched CO2 lasers. This system, which is the simplest short-pulse CO2 laser yet constructed, includes a pulsed power supply, a high-speed step-up transformer, a storage capacitor, and a laser tube. At high pressure (4.2 kPa and above), a rapid discharge produces a short laser pulse with a sharp spike pulse. In mixed gas (CO2: N2: He = 1: 1: 2) at a pressure of 9.0 kPa, the laser pulse contains a spike pulse of 218 ns and has a pulse tail length of 16.7 μs.

The short pulse carbon dioxide laser versus the colorado needle tip with electrocautery for upper and lower eyelid blepharoplasty

Various techniques for blepharoplasty have been described, including those performed with the assistance of the short pulse carbon dioxide laser and those performed with the assistance of the Colorado microdissection needle attached to an electrocautery unit. Although the superiority of the carbon dioxide laser to cold steel has been demonstrated for the performance of eyelid blepharoplasty, no studies have ever compared the carbon dioxide laser to the Colorado needle. This is a paired comparison study in which 12 healthy patients underwent bilateral blepharoplasty of their upper and/or lower eyelids by a single surgeon. For each patient, a short pulse carbon dioxide laser was used on one side, and a Colorado needle attached to an electrocautery unit was used on the other. Intraoperative times were recorded. At five post-operative visits patients were evaluated for post-operative healing parameters including edema, erythema, scar width, and bruising. Finally, excised tissue was assessed histologically for thermal damage. Comparing both techniques, no difference in patient or physician-measured parameters of healing were noted up to 1 month post-operatively. However, Colorado needle assisted blepharoplasty resulted in slightly shorter intraoperative times. It also resulted in less thermal damage on a histologic level, although these differences were not clinically significant. For the performance of blepharoplasty, the Colorado needle tip with electrocautery offers benefits equivalent to those of the short pulsed CO2 laser but has the advantage of shorter intraoperative times and lower cost.