Disk Laser Research Articles

Double-pass optical parametric generator pumped by Yb thin-disk laser for efficient 1.4–2.9 µm mid-IR radiation generation

Many different fields benefit from the usage of light sources emitting in the mid-infrared wavelength range (2–10 µm). A rising need for precise and fast sources in the mid infrared (mid-IR) is reflected in the development of a high-power, picosecond mid-IR source capable of generation at high repetition rates. In this work, we present the optimization of an optical parametric generator, pumped by a 3 W portion of total power of the Yb:YAG thin-disk laser (1.3 ps, 90 kHz, 90 W) by comparing a single-pass and double-pass arrangement output parameters in terms of output power dependences on input power, efficiency, beam profiles, stability, and spectra. The output tunability of both arrangements spanned from 1459 nm to 2891 nm, with the upper limit being influenced by the limited transmission of the dichroic components used in the setup above 2700 nm. It was shown that the double-pass arrangement increases the output power, from 17 mW in the single-pass arrangement to 193 mW in the double-pass arrangement at 1459 nm, resulting in over ten-fold output power increase.

Ultrafast thin-disk laser oscillators as driving sources for high harmonic generation

Thin-disk laser oscillators can nowadays reach few tens of femtosecond pulses at gigawatt-level intracavity powers and megahertz-repetition rates becoming increasingly more powerful sources for intra-oscillator high harmonic generation (HHG). Currently, we can generate high harmonics in neon reaching photon energies of 70 eV, which we expect to increase toward 100 eV in the near future. In parallel, the achievable average and peak output powers of these oscillators in the range of 100 W and 100 MW, respectively, make these sources very promising to drive HHG in single-pass configuration after nonlinear pulse compression. Starting from transform-limited 30 to 50-fs soliton output soliton pulses of TDL oscillators, we will likely see these lasers approaching a single-cycle regime becoming highly attractive sources for attosecond science.

Pound-Drever-Hall locking scheme free from Trojan operating points.

The Pound-Drever-Hall (PDH) technique is a popular method for stabilizing the frequency of a laser to a stable optical resonator or, vice versa, the length of a resonator to the frequency of a stable laser. We propose a refinement of the technique yielding an "infinite" dynamic (capture) range so that a resonator is correctly locked to the seed frequency, even after large perturbations. The stable but off-resonant lock points (also called Trojan operating points), present in conventional PDH error signals, are removed by phase modulating the seed laser at a frequency corresponding to half the free spectral range of the resonator. We verify the robustness of our scheme experimentally by realizing an injection-seeded Yb:YAG thin-disk laser. We also give an analytical formulation of the PDH error signal for arbitrary modulation frequencies and discuss the parameter range for which our PDH locking scheme guarantees correct locking. Our scheme is simple as it does not require additional electronics apart from the standard PDH setup and is particularly suited to realize injection-seeded lasers and injection-seeded optical parametric oscillators.

Intracavity third-harmonic generation in a continuous-wave/self-mode-locked semiconductor disk laser

The high peak power of picosecond pulses produced by a self-mode-locked semiconductor disk laser can effectively improve the efficiency of nonlinear frequency conversion. This paper presents the intracavity frequency tripling in a self-mode-locked semiconductor disk laser, and a picosecond pulse train at 327 nm wavelength is achieved. The pulse repetition rate is 0.49 GHz, and the pulse width is 5.0 ps. The obtained maximum ultraviolet output power under mode locking is 30.5 mW, and the corresponding conversion efficiency is obviously larger than that of continuous-wave operation. These ultraviolet picosecond pulses have high spatial and temporal resolution and can be applied in some emerging fields.

Wavelength-tunable multi-point pump semiconductor disk laser based on an intra-cavity transmission grating

We report a wavelength-tunable multi-point pump scheme of the semiconductor disk lasers (SDLs). By designing an external cavity of SDL with an intra-cavity transmission grating, multiple pump gain regions share the same resonator. The effect of the intra-cavity grating on the output laser power, wavelength, and beam quality was investigated. The emission wavelength could be tuned over a bandwidth of ∼18 nm. With multi-point pumping, we achieve the laser output power with almost no loss, and further improvement is limited by the thermal effect. The changes in the beam are due to the mode selectivity by the intra-cavity grating.

Percutaneous Laser Disc Decompression for Lumbar Radicular Pain: A Systematic Review of Pubmed in the Last Five Years

Percutaneous Laser Disc Decompression for Lumbar Radicular Pain: A Systematic Review of Pubmed in the Last Five Years

Comparison of Clinical Effectiveness between the Management of Cervical and Lumbar Disc Herniation with Percutaneous Laser Disc Decompression Followed by Interlaminar Cervical Epidural and Lumbar Transforaminal Epidural Steroid Injection Respectively

Background: Different treatments for discogenic axial back/neck pain or radicular pain to limbs are there from conservative therapies and minimally invasive therapies to open spine surgeries with lots of controversial outcomes. Percutaneous laser disc decompression (PLDD) is one of the minimally invasive therapies which is done under local anesthesia and has been successfully performed in many selected patients for their lumbar and cervical disc herniation problems. In PLDD, a part of the nucleus pulposus is vaporized with the help of laser energy to reduce the intradiscal pressure of the diseased discs causing nerve compression. In this case series after a 1-year follow-up, the clinical effectiveness of PLDD with epidural steroid injection is assessed in selected lumbar and cervical disc herniation cases. Materials and Methods: Ninety-six patients underwent the PLDD procedure at the cervical and lumbar disc with epidural steroid injections for their disc herniation causing radicular pain in the upper and lower limbs, respectively. The patients were followed at 8 weeks, 3 months, 6 months, and 1 year. The main outcome measures were done through the visual analog scores (VASs) and the Oswestry Disability Index (ODI) for upper and lower limb pain. Results: The primary outcome showed that there is a significant clinically relevant difference between the two groups at a 1-year follow-up. VAS and mean disability score based on the ODI were significantly lower in cervical disc herniation patients. The reoperation rate in the cervical group is also much less than the lumbar group. Conclusion: Like all other surgical modalities for disc herniation, PLDD has its own advantages and disadvantages. However, compared to lumbar disc herniation, it may give better results in cervical disc herniation. In selected cases, combined PLDD with epidural steroid injection can be chosen as a “first-choice-minimally-invasive-treatment,” when standard conservative therapies do not give satisfactory outcome.

Vaporization Modeling and Experimental Verification During Laser Beam Welding for 24Mn Steel

Vaporization modeling and experimental verification of the alloying elements that occurred during laser beam welding (LBW) of high-manganese steel were conducted. LBW using a disk laser and bead-on-plate testing was performed. Through modeling calculations at temperatures higher than 2800 K, the vapor pressure of Mn was found to be significantly larger than that of the other alloying elements. Furthermore, the vaporization flux of Mn was at least 10 times larger than that of the other alloying elements. The composition of the laser weldment was confirmed through electron probe microanalysis (EPMA), and a 1.8-wt% Mn reduction was observed in the laser weldment compared with the base metal composition. The composition of the other alloying elements, such as Fe, Cr, Si, and C, in the laser weldment was similar to that in the base metal.

Optimization of the gain chip for optically pumped semiconductor disk lasers

Strain-compensated quantum wells (QWs) could greatly improve the performance of semiconductor disk lasers, such as improving the epitaxy quality of the semiconductor gain chip and obtaining a higher gain. To optimize the output characteristics of the semiconductor gain chip, the strain-compensated thickness, well depth, band energy, emission wavelength, and peak gain versus In and P compositions are investigated in detail. The results show that increasing the P composition of the strain-compensated layer will slightly reduce the emission wavelength, deepen the well depth, and increase the peak gain. But the P composition is not the higher the better. When designing a gain chip, it should have a pre-offset between the emission wavelength of the QWs at room temperature and the target wavelength of the laser at an intense pump, and the pre-offset values of the wavelength should be designed deliberately to guarantee the resonant periodic gain structure working normally when the temperature in the active region approaches the desired value. This theoretical investigation may provide guidance for optimizing the laser performance of semiconductor disk lasers and other QW lasers.

Optimizing the Cavity-Arm Ratio of V-Shaped Semiconductor Disk Lasers

Passively mode-locked semiconductor disk lasers have received tremendous attention from both science and industry. Their relatively inexpensive production combined with excellent pulse performance and great emission-wavelength flexibility make them suitable laser candidates for applications ranging from frequency-comb tomography to spectroscopy. However, due to the interaction of the active medium dynamics and the device geometry, emission instabilities occur at high pump powers and thereby limit their performance potential. Hence, understanding those instabilities becomes critical for an optimal laser design. Using a delay-differential equation model, we are able to detect, understand, and classify three distinct instabilities that limit the maximum achievable pump power for the fundamental mode-locking state and link them to characteristic positive-net-gain windows. We furthermore derive a simple analytic approximation in order to quantitatively describe the stability boundary. Our results enable us to predict the optimal laser-cavity configuration with respect to positive-net-gain instabilities and therefore may be of great relevance for the future development of passively mode-locking semiconductor disk lasers.

CORROSION RESISTANCE OF LASER WELDED SHEETS OF STAINLESS STEEL 316L

The autogenous laser welding with a disk laser was used for producing butt joins of 2.0 mm thick sheets of AISI 316L stainless steel. The influence of basic laser welding parameters on the shape, microhardness distribution, microstructure and corrosion resistance of the joints was determined. The tests of corrosion resistance were conducted in a salt chamber under artificial NaCl environment conditions. The corrosion tests were conducted in accordance with the PN EN ISO 9227 standard. The produced test joints of 2.0 mm thick stainless steel were characterized by high quality, homogeneous and low-grained microstructure, and very narrow heat affected zone. The results of microhardness measurements indicated that the fusion zone was slightly hardened comparing to the 2.0 mm thick stainless steel sheet AISI 316L. The obtained results of corrosion test under artificial NaCl environment conditions showed that the tested butt joints are resistant for corrosion under the test conditions.

Repetition-rate-tunable second harmonic generation in mode-locked optically pumped semiconductor disk laser

We demonstrated a repetition-rate-tunable second harmonic mode-locked optically pumped semiconductor disk laser (OP-SDL), and the tuning range was from 1.168 GHz to 1.25 GHz. The entire tuning process was continuous, and OP-SDL was always in a mode-locked working state. To the best of our knowledge, this is the first work to obtain intracavity repetition rate tunable second harmonic laser in an OP-SDL. At same time, the repetition rate of fundamental wave can be continuously adjusted from 1.16 GHz to 1.66 GHz. The central wavelengths of the pulse trains were around 971 nm, and the highest repetition rate signal-to-noise ratio was more than 60 dB, indicating that the mode-locked pulses were stable.

Ultrasound-guided Percutaneous Laser Disc Decompression (PLDD) with Fluoroscopic Validation for the Treatment of Cervical Disc Herniation: Technical Note.

Percutaneous laser disc decompression (PLDD) has been regarded as an effective alternative for the treatment of cervical soft disc herniations. Repeated X-Ray scanning is essential when performing this technique. Technical note. We present a new method for the treatment of cervical disc herniation using ultrasound to guide the needle entry to the cervical disc, to avoid excess of radiation exposure during the surgical procedure. We evaluated the efficacy of this cervical approach. We retrospectively reviewed the clinical data of 14 cases who underwent a PLDD under ultrasound guidance for the treatment of contained cervical disc herniation using a 1,470 Nm diode laser. The lower cervical discs (C5-C6 and C6-C7) were the most affected sites, accounting for 78.6% of surgical discs. A significant NRS reduction between baseline and 1 month (P = .0002) and between baseline and 12 months (P = .0007) was observed. Our results support the conclusion that ultrasound guided PLDD with fluoroscopic validation is a minimally invasive technique for patients affected by herniated cervical discs, but proper choice of patients is critical. This approach should not be performed except after adequate training under close supervision of surgeons experienced in this procedure and in interventional US.

Personalized neurosurgical tactics in the treatment of intervertebral hernias of the lumbar spine

Objective. Analysis of literature data of modern neurosurgical techniques in the treatment of lumbar disc herniation; clarification of the features of surgical tactics and results during microsurgical, endoscopic methods and laser thermoplastic of the intervertebral disk. Methods. A retrospective analysis of the results of conventional microdiscectomy (228 cases), laser disc decompression (22 observations) and percutaneos endoscopic discectomy (4 observations) for lumbar disc herniation from 2016 to 2018. The results of surgical treatment was assessed according to the Oswestry Disability Index (ODI), Visual Analog Scale (VAS), modified MacNab criteria, and morphometric data of MRI and CT scans during the preoperative and postoperative periods, as well as 6 and 12 months after surgery. Results. The result of the study was a comparison of the literature data with those obtained in our clinic in the treatment of patients using all the indicated methods. On our material, we received confirmation of the feasibility and perspectivity of using minimally invasive methods in the treatment of lumbar disc herniation with low probability of recurrence and repeated treatment for pain. Also agree with the statement that the techniques have limited application, especially with instability in the VMS and multilevel lesion. Conclusion. Endoscopic discectomy, as well as laser disc decompression, are minimally invasive methods of treatment lumbar disc herniation, and have become an alternative to open lumbar microdiscectomy, as they allow minimizing surgical trauma, the effects of surgery, and quickly regress pain syndrome, contributing to early post-operative activation of the patient. A personalized approach in the treatment of lumbar disc herniation is based on the competent selection of patients and the clarification of a number of factors in determining.

Dynamics Simulation of Self-Mode-Locking in a Semiconductor Disk Laser Using Delay Differential Equations

Self-mode-locked semiconductor disk lasers possess compact resonant cavity and stable construction. These devices have a wide application prospect because of their picosecond to sub-picosecond pulse width, excellent beam quality and tailorable emission wavelength. In this paper, dynamics simulations of self-mode-locking in a semiconductor disk laser are performed by using delay differential equations for the first time. The corresponding conditions of different modality of mode-locking, including Q-switched mode-locking, continuous-wave mode-locking and harmonic mode-locking are calculated, and their dynamics evolution processes are presented. We also analyze the characteristics of the three different mode-locking modalities and summarize their overall dynamics evolution tendency. This kind of numerical simulation and analysis provides an understanding of the dynamics process of self-mode-locking, and may be referenced for related experiments.

Percutaneous Laser Disc Decompression (PLDD) for the Treatment of Contained Lumbar Disc Herniation.

Lumbar disc herniation is a common cause of back and radicular leg pain. A bulging annulus and contained herniated disc can compress a nearby exiting root as it enters the neuroforamen and may cause pain and neurological symptoms. Percutaneous laser disc decompression (PLDD) has been regarded as an effective alternative to microdiscectomy for the treatment of contained lumbar disc herniations. However, there is no consensus regarding the type of laser to use, the ideal wavelength, or the energy applied. The ideal laser irradiation should have a high water absorption coefficient and low tissue pervasion, to limit thermal injury. The 1470 nm wavelength of the diode laser is absorbed by water 40 times more effectively than the 980 nm wavelength. We conducted this study to evaluate the efficacy and safety of PLDD using a 1470 nm diode laser. We retrospectively reviewed the clinical data of 27 patients with radicular pain who underwent PLDD for the treatment of contained lumbar disc herniation during a 12-month period. The 1470 nm diode laser produces smaller local lesions, but greater tissue variations around the nucleus pulposus. This higher affinity for water lessens the formation of a carbonization zone, which results in less thermal injury of the adjacent nervous tissue. According to the MacNab criteria, 85.2% of the cases were improved at 6-month follow-up. Pain decreased from VAS 8.1 preoperatively to VAS 3.1 postoperatively. There is no consensus in the international literature regarding the ideal wavelength. Our results support the conclusion that PLDD using a 1470 nm diode laser is a safe and effective minimally invasive technique for patients with radicular pain affected by contained herniated lumbar discs.

Hybrid membrane-external-cavity surface-emitting laser.

We develop, analyze, and demonstrate an optically-pumped semiconductor disk laser using an active mirror architecture formed by sandwiching the semiconductor gain membrane between two heatspreaders, one of which is coated with a high-reflectivity multilayer. Thermal modeling indicates that this structure outperforms traditional VECSELs. Employing an InGaAs/GaAs MQW gain structure, we demonstrate output powers of approximately 30 W at a center wavelength of λ ≈ 1178 nm in a TEM00 mode using an in-well pumped geometry.

SELECTIVE SURFACE HARDENING OF GEAR MECHANISM SHAFT BY ROBOTIC LASER 3D SYSTEM

A robot-based laser 3D hardening method is proposed as a finishing operation to increase the wear resistance of the metal end-products. The laser hardening process of the surface layer of the products by changing its structure is one of the most effective methods of selective surface hardening. Thermal hardening of metals and alloys by laser radiation is based on local heating of a surface area under the influence of radiation and subsequent cooling of this surface area at a supercritical speed due to heat removal into the inner layers of the metal. The used robot-based laser 3D system (FANUC industrial robot and SCANLAB scanning optics) allows processing the surfaces of any complexity and geometry, including the shafts of the gear mechanism of the seed drill. It was found that the development and improvement of the technological process of manufacturing steel shafts of the gearbox of the seed drill is an urgent technological problem due to the rapid retirement of the shaft, which leads to the expenditure of time and money for its replacement. The most heavily loaded sections of the shaft were pre-estimated using the SolidWorks Simulation software package. A high-power TruDisk 8002 solid-state disk laser with a maximum laser power of 8 kW and a wavelength of laser radiation of 1030 nm is used for high-quality laser surface treatment of the AISI 1066 steel shaft of the gear mechanism. The laser surface heat treatment was carried out using a constant power strategy (continuous mode), varying the laser power in the range of 1.35–2.25 kW. Based on the Fe-Mn two-component state diagram, the critical points of the temperature of complete austenization of the studied steel were previously predicted taking into account the chemical composition of the material. Additionally, the energy density values of the laser beam with a diameter of 1 mm on the working surface was estimated. The results showed that the surface hardness of the shaft was about 2.5 times higher compared to the untreated surface. The working ranges of laser heat treatment parameters of the gearbox shaft were established to increase the hardening intensity (100–150%) of the responsible areas.

Fluorescence Radiation and Thermal Effect at the Edge of the Disk-Shaped Laser Crystal

The fluorescence radiation property at the edge of the thin disk crystal is very important to the design of thin disk lasers. In order to study this effect, in this paper, we established a theoretical model to describe the edge fluorescence radiation process in thin disk lasers. Subsequently, we used a thin disk crystal with indium absorption cladding to quantitatively test the edge fluorescence intensity. The significant difference between measured and simulated data can be described as P (probability value) < 0.1 at the edge when the measured temperature is lower than the melting point of the metal cladding, and P < 0.05 at the pump area. Finally, we analyze the influence of the edge fluorescence radiation on the thin disk laser operation, and the results show that the edge thermal effect will reduce the conversion efficiency of the disk laser by 20%. To the best of our knowledge, this is the first quantitative study on the edge radiation intensity of disk lasers. The research can provide theoretical guidance for the designing and packaging process of crystal elements in thin disk lasers.

Theoretical Investigations of High Power Yb3+: YAG Thin-Disk Laser

The present study includes a theoretical treatment to derive the general equations of pumping threshold power ( ), laser output power (Pout), and laser device efficiency (ƞ) of the element-doped thin-disk laser (Yb3+) with a quasi-three-level pumping scheme in the continuous wave mode at a temperature of (299K°). In this study, the host crystals (YAG) were selected as typical examples of this laser design in a Gaussian transverse mode. The numerical solution of these equations was made using Matlab software by selecting the basic parameters from the recently published scientific articles for the laser design of these crystal hosts. According to this simulation, this article studied the effect of concentration (N), pumping spot radius (rp), the number of times the pumping beam passes over the disk (Mp), and the pumping power on the laser output power.