Alternative Laser Sources Research Articles

Solid-state laser (266 nm) as an alternative to ArF excimer laser (193 nm) for corneal reshaping: Comparative numerical study of the thermal effect.

Laser corneal reshaping is a safe and effective technique utilized to treat common vision disorders. An advanced laser delivery system equipped with a pulsed UV laser with specific parameters is used to ablate parts of the cornea surface to correct the existing refractive error. The argon fluoride (ArF) excimer pulsed gas laser at 193 nm is the most employed type in the commercial devices for such treatments. This laser is generated using a mixture of Argon, Fluorine, and a significant amount of Neon gases. However, due to the ongoing Russian-Ukraine war, the availability of Neon gas is currently very limited, as this region is considered the primary supplier of pure Neon gas. Consequently we suggest replacing the common ArF laser source in the commercial devices with a solid-state (forth harmonic neodymium-doped yttrium aluminum garnet laser at 266 nm). This replacement uses the same operation parameters, optics, and scanning algorithm. Parameters from five commercial devices (Zeiss MEL 90, Technolas TENEO 317, Alcon Wave Light EX 500, Schwind Amaris 750 s, OptoSystems MICROSCAN VISUM) were compared with those of the i-ablation device, a research device that uses a 266 nm laser source. Our goal is to reduce production costs through a simple modification that has a significant impact. Consequently, the present study aims to find an alternative laser source for the current ArF laser without exchanging the complete system's design. This recommendation is based on a numerical simulation study. The thermal effect on a human cornea model was numerically evaluated using finite-element solutions of Pennes' bioheat equation on the COMSOL platform by applying two laser wavelengths. The results demonstrated that changing the laser source significantly impacts the thermal effect, even with the same laser settings. All studied devices showed a reduction in the thermal effect to below 40°C, compared with nearly 100°C under ordinary conditions.

Laser-based killing of a macroparasite inside its live invertebrate host

Whether host phenotypic alterations induced by parasites are reversible or not is a core issue to understand underlying mechanisms as well as the fitness costs of infection and recovery to the host. Clearing infection is an essential step to address this issue, which turns out to be challenging with endoparasites of large size relative to that of their host. Here, we took advantage of the lethality, contactless and versatility of high-energy laser beam to design such tool, using thorny-headed worms and their amphipod intermediate host as a model system. We show that laser-based de-parasitization can be achieved using blue laser targeting carotenoid pigments in Polymorphus minutus but not in the larger and less pigmented Pomphorhynchus tereticollis. Using DNA degradation to establish parasite death, we found that 80% P. minutus died from within-host laser exposure. Survival rate of infected gammarids to laser treatment was higher than uninfected ones. The failure to kill P. tereticollis was also observed with nanosecond-green laser, an alternative laser source targeting lipid. We discuss the possible causes of amphipod death following parasite treatment and highlight the perspectives that this technology offers.

Novel VECSEL for short‐wave infrared Raman spectroscopy applications

Raman spectroscopy of pigmented samples can be problematic owing to strong laser‐induced auto‐fluorescence. Moving the laser excitation more into the near‐infrared region (>900 nm) and detection to the short‐wave infrared region (SWIR) (1200–1600 nm) significantly decreases laser‐induced‐fluorescence for many pigmented samples. However, conventional near‐infrared diode‐lasers suitable for Raman spectroscopy are expensive. Vertical‐external‐cavity surface‐emitting lasers (VECSELs) are an interesting alternative laser source for Raman spectroscopy. VECSELs offer a narrow linewidth, high power stability, good power efficiency and circular beam profile characteristics, and their wavelength can be engineered over a broad range in the near‐infrared. In addition, they offer the potential of low‐cost mass production, and they are small in size. We developed a 986‐nm VECSEL for a specific biomedical application (Raman measurements of pigmented skin lesions). We implemented and tested the feasibility of the novel 986‐nm VECSEL in a SWIR multi‐channel Raman spectroscopy instrument. We have characterized the VECSEL in relation to the requirements set by this biomedical application and have demonstrated for the first time Raman spectra of pigmented skin lesion with a VECSEL in the SWIR region. Our results show that the VECSEL fulfils the requirements of a laser source to be applied in Raman spectroscopy. This opens the possibility of using VECSELs for low‐cost compact hand‐held Raman spectroscopy applications. Copyright © 2017 John Wiley & Sons, Ltd.

Laser source for dimensional metrology: investigation of an iodine stabilized system based on narrow linewidth 633 nm DBR diode

We demonstrated that an iodine stabilized distributed Bragg reflector (DBR) diode based laser system lasing at a wavelength in close proximity to nm could be used as an alternative laser source to the helium-neon lasers in both scientific and industrial metrology. This yields additional advantages besides the optical frequency stability and coherence: inherent traceability, wider optical frequency tuning range, higher output power and high frequency modulation capability. We experimentally investigated the characteristics of the laser source in two major steps: first using a wavelength meter referenced to a frequency comb controlled with a hydrogen maser and then on an interferometric optical bench testbed where we compared the performance of the laser system with that of a traditional frequency stabilized He–Ne laser. The results indicate that DBR diode laser system provides a good laser source for applications in dimensional (nano)metrology, especially in conjunction with novel interferometric detection methods exploiting high frequency modulation or multiaxis measurement systems.

A new process chain for producing bulk metallic glass replication masters with micro- and nano-scale features

A novel process chain for serial production of polymer-based devices incorporating both micro- and nano-scale features is proposed. The process chain is enabled by the use of Zr-based bulk metallic glasses (BMG) to achieve the necessary level of compatibility and complementarity between its component technologies. It integrates two different technologies, namely laser ablation and focused ion beam (FIB) milling for micro-structuring and sub-micron patterning, respectively, thus to fabricate inserts incorporating different length scale functional features. Two alternative laser sources, namely nano-second (NS) and pico-second (PS) lasers, were considered as potential candidates for the first step in this master-making process chain. The capabilities of the component technologies together with some issues associated with their integration were studied. To validate the replication performance of the produced masters, a Zr-based BMG insert was used to produce a small batch of micro-fluidic devices by micro-injection moulding. Furthermore, an experimental study was also carried out to determine whether it would be possible by NS laser ablation to structure the Zr-based BMG workpieces with a high surface integrity whilst retaining the BMG’s non-crystalline morphology. Collectively, it was demonstrated that the proposed process chain could be a viable fabrication route for mass production of polymer devices incorporating different length scale features.

Diode Laser Treatment of Human Prostates

Introduction: Laser-assisted vaporization of prostate tissue by means of the potassiumtitanyl-phosphate (KTP) laser is in clinical use. Alternative laser sources are available but are lacking clinical experience.The 980 nm wavelength diode laser provides good hemostasis, in addition to a more rapid ablation rate. The aim of this study is approving the capability, feasibility, and good post-operative outcome of vaporization of prostate by means of a diode laser in a long-term follow up. Methods: The light (980 nm, 100 W) of a diode laser was transmitted to prostate tissue. The study included 70 men suffering from bladder outlet obstruction due to benign prostatic hyperplasia (BPH). The prostatic lobes were vaporized within the prostatic capsule. Post-operative outcome and voiding were evaluated during a follow-up period of 24 months. Results: During surgery, no significant blood loss or any fluid absorption occurred. Catheters were removed in the 20.1±4.6 hours. All patients except two were satisfied with their voiding outcome. After removing the catheter, the mean peak urine flow rate significantly increased from 6.8±2.5 ml/s pre-operatively to 15.6±3.1 ml/s postoperatively. No evidence of urgency, dysuria, hematuria, or incontinence was observed. Four patients required re-catheterization, and two of them needed consecutive TURP. After a 1- month, as well as after a 6-month, a 12-mouth, and a 1-year follow-up, all patients were still satisfied with the outcome. Conclusion: This long term experience showed that 100 W-980 nm-diode-laser vaporization prostatectomy was feasible and appeared to be safe and effective for quickly relieving bladder outlet obstruction due to BPH.

Corneal ablation with new 193 nm solid-state laser: Preliminary experiments

To assess the ability of a newly developed 193 nm solid-state laser to ablate the cornea.Osaka University, Osaka, Japan.A prototype laser engine was developed by combining a 1547 nm laser diode, fiber amplifiers, and 5 stages of a frequency-conversion system using CsLiB6O10 crystals as the last stage. Poly(methyl methacrylate) (PMMA) plates were exposed to the prototype laser beam to determine the relationship between the fluence and ablation rate. Laser irradiation of porcine corneas was performed to induce morphological changes, and the quality of the lesions was determined by light and scanning electron microscopy.The relationship between the fluence and ablation rate of the 193 nm solid-state laser was comparable to that of the argon-fluoride excimer laser. Light and scanning electron microscopy of the porcine corneas showed that the linear and square lesions had sharp, clean edges.Smooth ablations of PMMA plates and porcine corneas were obtained by the laser. Further investigations must be conducted to determine whether this laser can be an alternative laser source for keratorefractive surgery.

Diode laser treatment of human prostates – Clinical 6-month experience

Abstract Objectives Laser-assisted vaporization of prostate tissue by means of the KTP laser is in clinical use. Alternative laser sources are available but are lacking clinical experience. In this study, the capability, feasibility, and post-operative outcome of vaporization of prostate by means of a diode laser were investigated. Methods The light (λ=1470 nm, 50 W) of a diode laser (Biolitec AG, Jena, Germany) was fed into a side-fire fiber introduced through a 24F continuous-flow cystoscope and thus transmitted to prostate tissue. Normal saline was used for irrigation with additive of 1% ethanol for observation of TUR syndrome. The study includes 10 men suffering from bladder outlet obstruction due to benign prostatic hyperplasia (BPH) (prostate volume range: 35–78 ml). The prostatic lobes were vaporized within the prostatic capsule. Depending on the vaporized tissue the exposure time was in the range of 1220–4000 s (mean: 2397±757 s) during which a mean of 121±38 kJ (range: 61–200 kJ) of energy was delivered. Post-operative outcome and voiding were evaluated during a follow-up of 6 months. Results During surgery no significant blood loss or any fluid absorption occurred. Catheters were removed in the mean after 50 h (range: 18–168 h). All patients excepted two, were satisfied with their voiding outcome. After removing the catheter the mean peak urine flow rate significantly (p=0.05) increased from 8.9±2.9 ml/s pre-operatively to 15.7±5 ml/s post-operatively. No evidence of urgency, dysuria, hematuria, or incontinence was observed. Two patients required re-catheterization and consecutive TURP. After 1 month as well as after 6-month follow-up, 8/10 patients are still satisfied with the outcome. Conclusion This first and limited experience showed that 50 W-1470 nm-diode-laser vaporization prostatectomy is feasible and appears to be safe and effective for quickly relieving bladder outlet obstruction due to BPH. Long-term efficacy and durability should be evaluated in a randomized clinical trial with long-term follow-up.

Mid infrared optical parametric oscillator (OPO) as a viable alternative to tissue ablation with the free electron laser (FEL)

Investigations with a Mark-III free electron laser, tuned to 6.45 microm in wavelength have demonstrated minimal collateral damage and high ablation yield in ocular and neural tissues. While the use of mid-IR light produced by the free electron laser (FEL) has shown much promise for surgical applications, further advances are limited due the high costs of its use. Further investigation and widespread clinical use of six-micron radiation requires the development of an alternative laser source. In this research, we compared a Mark-III FEL and an Er:YAG pumped ZGP-OPO with respect to the effect of pulse duration on ablation efficiency and thermal damage on porcine cornea. A five by seven grid of craters was made about the center of each cornea. Craters were made with a 60-microm spotsize with a 500-microm spacing. Ablation craters were made using 50 pulses per crater at approximately three times the ablation threshold (for water). Histological analysis was used to determine crater depth and thermal damage. The average zone of thermal damage at 6.1 microm was found to be 4.1 microm for the optical parametric oscillator (OPO) and 5.4 microm for the FEL. At 6.45 microm, the damaged zone was 7.2 microm for the OPO and 7.2 microm for the FEL. At 6.73 microm, the damaged zone was 6.3 microm for the OPO and 7.6 microm+/-0.3 microm for the FEL. The OPO caused similar or significantly less thermal damage in porcine cornea when compared with the FEL while generating significantly deeper craters. We determined that the ZGP-OPO has much promise as a bench-top replacement for the FEL for soft tissue ablation.

The effect of free-electron laser pulse structure on mid-infrared soft-tissue ablation: ablation metrics

Pulsed mid-infrared (6.45 µm) radiation has been shown to cut soft tissue with minimal collateral damage (<40 µm); however, the mechanism of ablation has not been elucidated to date. The goal of this research was to examine the role of the unique pulse structure of the Vanderbilt Mark-III free-electron laser (FEL) and its role in the efficient ablation of soft tissue with minimal collateral damage. The effect of the picosecond micropulse was examined by running the native FEL pulse structure through a pulse stretcher in order to increase the micropulse length from 1 ps up to ∼200 ps. This allowed us to determine whether or not the picosecond train of micropulses played any role in the ablation process. The ablation threshold was determined for water and mouse dermis for each micropulse length. While the results of the analysis showed a statistically significant difference between 1 and 200 ps, the average per cent difference amounts to only 28% and is not proportional to the 200-fold drop in peak irradiance. The ablation efficiency was also measured on gelatin and mouse dermis for the different micropulse lengths. A small but statistically significant difference was observed between 1 and 200 ps, with the 200 ps pulse being more efficient on gelatin, and with the opposite trend for mouse dermis. We have shown that there is a small effect of micropulse duration of the FEL on the ablation process; however, this effect is negligible between 1 and 200 ps given that there is a 200-fold decrease in peak intensity. These results suggest that as we move forward in developing alternative laser sources for tissue ablation to replace the FEL, the picosecond micropulse structure is not a critical parameter that needs to be duplicated.

Low-temperature synthesis and room temperature ultraviolet lasing of nanocrystalline ZnO films

Nanocrystalline ZnO films were fabricated via a simple method involving the oxidation of Zn films at a remarkably low temperature of 380 °C. X-ray diffraction study confirmed that the Zn films were completely oxidized even at the low temperature of 380 °C and the ZnO films fabricated were of polycrystalline wurtzite structure. Room temperature optical pumping using a frequency-quintupled Q-switched Nd:YAG laser (λ=213 nm) exhibited that sharp peaks at around 3.12 eV emerged above excitation powers of ∼7 MW/cm2, demonstrating lasing in the ZnO films. These results represent that the process is a simple, promising approach for fabricating ZnO of sufficient optical performance for use as ultraviolet (UV) light emitters and an alternative UV laser source; both are key components in short-wavelength photonic devices.

Impact of an Er:YAG laser beam control on cut quality of non-mechanical corneal trepanation for penetrating keratoplasty

Results of non-mechanical corneal trepanation using the excimer laser enhance the morphological and functional results for penetrating keratoplasty. Searching for alternative laser sources we assessed the impact of an automatic laser beam control for the Er:YAG solid-state laser on the cut performance and thermal damage zone in non-mechanical corneal trepanation. We compared the cut quality of A) a manually guided laser beam, B) a semiautomatically guided laser beam and C) a fully PC-controlled laser beam positioning system (q-switched, repetition rate 5 Hz, pulse energy 65 mJ, spot size 0.7 mm) along slit aperture masks on 28 rabbit eyes using macroscopic images and histological sections (PAS staining). The manually guided laser beam control (A) induced the broadest thermal damage zone in the corneal stroma (19.3+/-8.7 microm) compared to the semi-automatic mode (B) (8.8+/-3.0 microm, p=0.03) and the PC-controlled laser beam control (C) (7.0+/-3.0 microm, p=0.016). The fully automatic PC-controlled laser beam positioning system for the Er:YAG solid-state laser with a small spot size and fixed low repetition rate allows a precise laser beam guidance and a significant enhancement of the cut performance compared to a manual laser beam control via micromanipulator in experimental nonmechanical corneal trepanation.

1083 nm ytterbium doped fibre amplifier for opticalpumping of helium

A combination of a narrow linewidth, tunable DBR diode laser and high power ytterbium fibre amplifier in a master oscillator power fibre amplifier (MOPFA) configuration is demonstrated for efficient optical pumping of helium. A compact and efficient diode pumped prototype system is shown to compare favourably with alternative laser sources for production of hyperpolarised /sup 3/He using direct pumping for medical application in MRI.

In vitro Alexandrite laser angioplasty: A study on fibre conduction and tissue effects

Pulsed ultra-violet excimer laser radiation is capable of tissue ablation with only minimal thermal injury of adjacent tissue structures. Since difficult fibre optic coupling of energy was observed, alternative Q-switched laser sources capable of ablation of atherosclerotic plaque are under current investigation. To evaluate tissue effects of Alexandrite laser radiation, 160 arterial segments with macroscopic evidence of atherosclerotic disease were treated. The laser light was transmitted via silica based quartz fibres with different diameters. Using the Q-switched Alexandrite laser at the fundamental wavelength (748 nm) with a pulse duration of 300 ns the energy density threshold for tissue ablation was found to be in the range of 63 to 126 J cm−2 using a 300μm fibre. On macroscopic examination only limited thermal and acoustic injury was found in crater adjacent tissue structures. Crater edges were even and did not reveal signs of crater charring or debris in the crater lumen. However, the histological cross-sections revealed thermal injury extending from 100 up to 200μm lateral into adjacent tissue. The crater margins revealed fissuring as a result of shock wave injury. Thermal damage was most evident if irradiation of atherosclerotic tissue was performed in blood.