Lithium Triborate Research Articles

Widely Tunable High-Power Two-Color VECSELs for New Wavelength Generation

We report a collinear two-color vertical external cavity surface emitting laser (VECSEL), which with minimal changes is suitable for intracavity type I second harmonic generation (SHG), type II sum frequency generation (SFG), and type II difference frequency generation (DFG). The demonstrated two-chip cavity provides high-brightness, independently tunable two color, orthogonally polarized intracavity lasing modes. VECSEL chips with emission around 970 and 1185 nm allow the generation of a wide range of wavelengths in the visible and long-wavelength spectral range. The open cavity, collinear geometry, provided a platform for efficient SHG yellow output, SHG blue output, and SFG of green output in the same cavity while only changing the nonlinear crystals. In all cases for visible light generation, a lithium triborate nonlinear crystal is introduced in the cavity region where the fundamental beams are overlapped. Simultaneous SHG and SFG in the same cavity resulting in overlapped outputs consisting of two visible colors are also demonstrated. By using two VECSEL chips with similar gain peaks, intracavity terahertz generation by DFG is demonstrated for the first time in a T-cavity VECSEL geometry. A custom-made tilted periodically poled lithium niobate nonlinear crystal generated DFG signal around 1 THz.

Photoselective Vaporesection of the Prostate with a Front-firing Lithium Triborate Laser: Surgical Technique and Experience After 215 Procedures

BackgroudAlthough photoselective vaporization of the prostate (PVP) is considered one of the most promising alternatives to transurethral radical prostatectomy, a longer operative time, an unsatisfactory tissue removal rate, and the absence of postoperative pathology samples remain the main criticisms for this procedure. ObjectiveTo describe the novel technique of photoselective vaporesection of the prostate (PVRP) with a front-firing lithium triborate (LBO) laser and to report our initial experience. Design, setting, and participantsThis is a prospective study of 215 patients undergoing PVRP between November 2011 and March 2013. Their average age, prostate size, and International Prostate Symptom Score (IPSS) were 70.3±7.3 yr, 70.4±34.0ml, and 24.9±5.0, respectively. Surgical procedureThe operative technique is detailed in the accompanying video. Outcome measurements and statistical analysisPerioperative data were collected. The patients were followed up at 3, 6, 12 mo after PVRP, and functional outcomes and complications were assessed. Results and limitationsThe mean operation time was 44.1±22.6min. The mean hemoglobin decrease was 0.37±0.21g/dl. The catheterization time was 23.9±15.2h and the postoperative hospital stay was 1.8±0.8 d. Significant improvements were observed in maximum flow, IPSS, and postvoid residual urine at each follow-up time point. Compared to preoperative values, prostate volume and serum prostate-specific antigen fell by 67% and 63%, respectively, at 3 mo after PVRP. No major complications were noted. Application of a hemostat for a front-firing LBO laser makes it easy to handle intractable intraoperative bleeding. The main limitation of this study is the short follow-up period. The influence of PVRP on sexual function and the learning curve remain to be evaluated. ConclusionsPVRP is a novel technique that is effective and safe for treatment of benign prostatic hyperplasia. This technique retains the excellent hemostatic property of LBO lasers and has a short operation time and a high tissue removal rate. The problem of the lack of postoperative tissue samples for PVP is also overcome in PVRP. Patient summaryWe have developed a novel technique named photoselective vaporesection of the prostate (PVRP) with a front-firing green laser. Our results show that PVRP retains the excellent hemostatic property of a green laser, but has a much shorter operation time and a higher rate of tissue removal than photoselective vaporization of the prostate (PVP). This technique also solves the problem of the lack of postoperative tissue specimens and the difficulty of handling intractable intraoperative bleeding. According to our initial results, PVRP is a novel technique superior to PVP in the treatment of benign prostatic hyperplasia.

The massively enlarged prostate: experience with photoselective vaporization of the ≥100 cc prostate using the 180 W lithium triborate laser.

To determine if there is a role for high-powered photoselective vaporization of the prostate (PVP) in large prostates for the management of bladder outlet obstruction. This study aims to evaluate the safety and efficacy of PVP in prostates ≥100 cc. A retrospective analysis of a prospectively maintained database (ethics approved), single-surgeon, single-center series, between November 2010 and February 2013 of males with ≥100 cc prostates who underwent PVP. Perioperative and functional outcomes at baseline, 3, and 6 months were evaluated. Thirty-five males were identified, median age 70 (interquartile range [IQR] 66-79) with prostates ≥100 cc (median 132, IQR 118-157). Preoperatively, 11/35 (31%) were in urinary retention and 11/35 (31%) were anticoagulated. Perioperative outcomes showed median laser time 75 minutes, operating time 103 minutes, and energy use 750 kJ. Median postoperative length of stay was 20 hours, catheterization 12 hours, and 33/35 (94%) were discharged catheter free. Twelve adverse events in 11 men were recorded, all Clavien-Dindo Grade I-II with 1 Grade IIIa complication. Paired functional outcomes showed statistically significant (p<0.05) improvements in the median International Prostate Symptom Score (IPSS) (20, 6, 6), quality of life (QoL) Index (4, 1, 1), maximum urinary flow rate (Qmax) (9.5, 20.5, 19.5 mL/s), and postvoid residual (149, 40, 41 mL) (baseline, 3, and 6 months). PVP using the 180 W LBO laser in large prostates appears feasible and efficacious, with short duration of catheterization and postoperative length of stay. Acceptable morbidity was recorded. Enormous energy utilization was delivered within acceptable operating times. Early results indicate excellent functional outcomes at 3 and 6 months following PVP.

Characteristics of optical parametric oscillators synchronously pumped by second harmonic of femtosecond Yb:KGW laser

We present experimental data and numerical simulation results obtained during investigation of synchronously pumped optical parametric oscillators (SPOPOs) pumped by second harmonic (515nm) of femtosecond Yb:KGW laser. We used two different nonlinear media for parametric generation – lithium triborate (LBO) and beta barium borate (BBO) in slightly different experimental setups. Maximum parametric light conversion efficiency from pump power to signal power was more than 25% whereas the largest achieved signal wave tuning ranges were from 670nm to 1030nm for BBO SPOPO and from 780nm to 940nm for LBO SPOPO. We also used intracavity group delay dispersion (GDD) compensation to achieve shorter signal pulses and investigated changes of various SPOPO output characteristics when changing net cavity GDD.

Bandwidth analysis of type-I optical parametric chirped pulse amplification systems

We propose a set of empirical formulas to describe the signal broadband gain regime and ultra-broadband gain point under a given pump wavelength for a type-I optical parametric chirped pulse amplification (OPCPA) system. These formulas are applied in the usual nonlinear crystals (beta barium borate, potassium dihydrogen phosphate, deuterated potassium dihydrogen phosphate, cesium lithium borate, lithium triborate, and yttrium calcium oxoborate), and the corresponding results agree with numerically calculated ones. The empirical formulas provide guidelines for selecting appropriate crystals or pump wavelengths to design OPCPA for broadband or ultra-broadband gain bandwidths with appointed signal wavelength.

Growth of lithium triborate (LiB3O5) single crystals in the Li2O-B2O3-MoO3 system

Solubility curves are plotted and optimal solvents for growing lithium triborate (LiB3O5) single crystals are determined. The crystallization range of this compound in the Li2O-B2O3-MoO3 system is refined. The molybdenum content in the crystals grown is analyzed.

Detrusor Overactivity Does Not Predict Bothersome Storage Symptoms After Photoselective Vaporization of the Prostate With Lithium Triborate Laser

To find out if detrusor overactivity (DO) is a predictor of moderate or severe storage lower urinary tract symptoms (LUTS) persisting 6 months after photoselective vaporization of the prostate (PVP). Patients with bladder outlet obstruction proved by urodynamics who underwent PVP with the lithium triborate laser were followed for 6 months with the International Prostate Symptom Score (IPSS) questionnaire. Moderate-to-severe storage LUTS were defined as IPSS storage domain score >8 and/or a score for an IPSS question on urgency >3. Predictive values of DO, IPSS domains, urgency, prostate volume, bladder outlet obstruction grade, and energy used were tested by logistic regression analysis. Seventy-six men at the age of 66.4 ± 6.8 years underwent PVP, including 36 (47.4%) with DO. Incidence of moderate or severe storage LUTS was decreasing from 60.5% to 48.7% at week 6 and 11.8% at month 6 postoperatively. At a univariate analysis, urgency score and storage domain score were significantly associated with bothersome storage LUTS at month 6. Multivariate analysis confirmed predictive value of preoperative urgency having an odds ratio of 5.7 (95% confidence interval, 1.41-23.16; P = .014). DO was not associated with the defined outcome. In our group, DO was not useful in predicting persistent storage symptoms after PVP. Patients with severe preoperative urgency should be informed about a risk of such outcome.

Common trend: move to enucleation-Is there a case for GreenLight enucleation? Development and description of the technique.

BackgroundTransurethral laser prostatectomy has evolved as a viable alternative for the management of benign prostate enlargement. Since the renaissance of laser prostatectomy with the advent of the holmium:yttrium–aluminum–garnet laser in the 1990s, various lasers and subsequent procedures have been introduced. These techniques can be categorized as vaporizing, resecting, and enucleating approaches. Photoselective vaporization of the prostate (PVP) is dominated by high-power lithium triborate (LBO) crystal lasers (GreenLight XPS). The mainstay of this technique is for the treatment of small to medium prostate volumes whereas enucleating techniques, such as holmium laser enucleation of the prostate and thulium enucleation of the prostate, focus on large-volume glands. In order to perspectively “delimit” LBO into the field of large-volume prostates, we developed LBO en bloc enucleation to render it as a competing transurethral enucleating approach.Materials and methodsWe present a detailed stepwise progressive technique developed in Madrid, Spain, for the complete removal of the transitional zone by vapoenucleation. The steps include exposition of the prostatic capsule by PVP toward the peripheral zone, thereby identifying the anatomical limits of enucleation. Subsequently, the transitional zone is excised in a single bloc and morcellated after its placement into the bladder.Conclusion This new GreenLight en bloc enucleation technique allows to treat larger prostates than those previously treated with the PVP technique.

Lossless directional guiding of light in dielectric nanosheets using Dyakonov surface waves.

Guiding light at the nanoscale is usually accomplished using surface plasmons. However, plasmons propagating at the surface of a metal sustain propagation losses. A different type of surface excitation is the Dyakonov surface wave. These waves, which exist in lossless media, were predicted more than two decades ago but observed only recently. Dyakonov surface waves exist when at least one of the two media forming the surface exhibits a suitable anisotropy of refractive indexes. Although propagating only within a narrow range of directions, these waves can be used to create modes supported by ultrathin films that confine light efficiently within film thicknesses well below the cutoff thickness required in standard waveguides. Here, we show that 10 nm and 20 nm dielectric nanosheets of aluminium oxide clad between an anisotropic crystal (lithium triborate) and different liquids support Dyakonov-like modes. The direction of light propagation can be controlled by modulating the refractive index of the cladding. The possibility of guiding light in nanometre-thick films with no losses and high directionality makes Dyakonov wave modes attractive for planar photonic devices in schemes similar to those currently employing long-range plasmons.

Efficient frequency doubling at 399 nm.

We describe a reliable, high-power, and narrow-linewidth laser source at 399 nm, which is useful for cooling and trapping of ytterbium atoms. A continuous-wave titanium-sapphire laser at 798 nm is frequency doubled using a lithium triborate crystal in an enhancement cavity. Up to 1.0 W of light at 399 nm has been obtained from 1.3 W of infrared light, with an efficiency of 80%.

High Brightness 556 nm Laser by Frequency Doubling of a 1112 nm Nd:YAG Laser

We demonstrate an efficient high power and high brightness yellow-green 556-nm laser generated from second harmonic generation (SHG) of a master oscillator power amplifier (MOPA) laser system at 1112 nm. The oscillator was a pulsed laser diode (LD) pumped and Q-switched Nd:YAG laser at 1112 nm operated at TEM <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">00</sub> mode with an average output power of 35 W, providing 200-μs long macropulses and constituting 700-ns micropulses. The seed laser was amplified by two LD side-pumped Nd:YAG amplifiers and the MOPA system delivered a maximum output power of 78 W. Using a type-I phase-matching lithium triborate nonlinear crystal, the SHG maximum output power of 48 W was obtained at 556 nm with a conversion efficiency as high as 61.5%. The beam quality factor was measured to be M <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> = 1.53 and the corresponding brightness was as high as 6.63 × 10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">9</sup> W/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> ·sr.

A diode-end-pumped continuous-wave single-longitudinal-mode Nd:GdV O4–LBO red laser at 670 nm

A diode-end-pumped continuous-wave single-longitudinal-mode intracavity frequency-doubling Nd:GdV O4–LBO (lithium triborate) red laser at 670 nm is reported. A ring cavity was designed to enable single-longitudinal-mode operation of the laser. By optimizing the mode-to-pump ratio taking account of the influence of the laser beam radius inside the frequency-doubling crystal LBO on the frequency-doubling efficiency for the special cavity, a maximum output power of 1.3 W for a continuous-wave single-longitudinal-mode red laser at 670 nm was obtained, and the measured power stability was better than ±1.2% in 2 h. The experimental results are in good agreement with the theoretical calculation.

Efficient second to ninth harmonic generation using megawatt peak power microchip laser

We report the design and use of a megawatt peak power Nd:YAG/Cr4+:YAG microchip laser for efficient second to ninth harmonic generation. We show that the sub-nanosecond pulse width region, between 100 ps and 1 ns, is ideally suited for efficient wavelength conversion. Using this feature, we report 85% second harmonic generation efficiency using lithium triborate (LBO), 60% fourth harmonic generation efficiency usingß-barium borate, and 44% IR to UV third harmonic generation efficiency using Type I and Type II LBO. Finally, we report the first demonstration of 118 nm VUV generation in xenon gas using a microchip laser.

Low repetition rate, hybrid fiber/solid-state, 1064 nm picosecond master oscillator power amplifier laser system

We report on an investigation of a passively mode-locked picosecond ytterbium-doped fiber laser with a repetition rate close to 1 MHz. The mode-locking operation was induced by a butt-coupled semiconductor saturable absorber mirror (SESAM) and stabilized in the normal dispersion regime by means of spectral filtering of a narrow bandwidth (0.1 nm) fiber Bragg grating (FBG). A pulse duration of about 50 ps with maximum output power of 20 mW at 1064 nm were achieved after amplification in the double-pass fiber preamplifier. This compact and reliable all-fiber laser operating at 1064 nm is intended to seed bulk amplifiers in a hybrid fiber/solid-state configuration. Employing a two-stage Nd:YVO4 amplifier, we obtained 10 W average output power, which preserved both the quasi-diffraction limited beam quality and spectral purity of the seeder. Second harmonic generation (SHG) with 50% conversion efficiency was demonstrated in type-II potassium titanyl phosphate (KTP) and type-I angle phase matched lithium triborate (LBO) crystal. Furthermore, a space independent numerical model was developed in order to study the dependence of intracavity pulse energy on the main design parameters of the master oscillator (cavity length, FBG bandwidth, SESAM modulation depth) within the stability range (single pulse per round trip in CW mode-locking operation) of the fiber laser master oscillator.

Optical properties of borate crystals in terahertz region

In this paper we study the optical properties of a family of borate crystals comprising alpha and beta barium borates, barium fluoroborate, lithium triborate, and lithium tetraborate in the frequency range from 0.3 to 2.0THz. We extract the refractive indices and absorption coefficients for both ordinary and extraordinary beams from terahertz time-domain spectroscopy data. All of the investigated crystals exhibit substantial birefringence and dichroism, which qualifies them as potential materials for terahertz polarization-optical devices. We also find an additional absorption band in barium borate crystals, which is not defined by the group of phonon modes lying above 2THz. We argue that this phenomenon may be caused by excessive sodium atoms and ions in the crystal lattice.

Intracavity pumped sum-frequency mixing for an emission at 491.5 nm

We present an Nd:LuVO4 laser emitting at 1066 nm intracavity pumped by a 912 nm diode-pumped Nd:GdVO4 laser. A 880 nm diode laser is used to pump the Nd:GdVO4 crystal emitting at 912 nm, and the Nd:LuVO4 laser emitting at 1066 nm intracavity pumped at 912 nm. Intracavity sum-frequency mixing at 912 and 1066 nm was realized in a lithium triborate crystal to reach the blue range. We obtained a continuous-wave output power of 2.35 W at 491.5 nm with a pump laser diode emitting 26.2 W at 880 nm. The power stability is better than 3.5% and the laser beam quality M2 factors are 1.31 and 1.23 in the horizontal and vertical dimensions respectively.

Palm-top size megawatt peak power ultraviolet microlaser

The development of a very compact, highly efficient, megawatt peak power, subnanosecond pulse width, 266 nm ultraviolet (UV) microlaser is reported. It contains a specially designed passively Q-switched Nd∶YAG/Cr 4+ ∶YAG microchip laser whose high output peak power of 13 MW enables an efficient wavelength conversion without using any optics before the nonlinear crystals. The subnanosecond pulse width region, which delivers high peak power even at moderate pulse energy, is very useful for an efficient wavelength conversion. We achieve 73% second harmonic generation efficiency using a LiB 3 O 5 (lithium triborate) crystal and 45% fourth harmonic generation efficiency using a β−BaB 2 O 4 (β -barium borate) crystal. As a result, we obtain 650 μJ, 4.3 MW peak power, 150 ps, and 100 Hz pulse output at 266 nm. We use an original design for the nonlinear crystal holders to reduce the size of the microlaser. This palm-top size 266 nm UV microlaser will be useful for many applications, such as materials microprocessing, pulsed laser deposition, UV laser induced breakdown spectroscopy, and photoionization.

Multiwatt, Continuous-Wave, Tunable Diamond Raman Laser With Intracavity Frequency-Doubling to the Visible Region

Multiwatt emission from a continuous-wave diamond Raman laser pumped within a diode-pumped InGaAs-based semiconductor disk laser (SDL) is reported. The Raman laser achieved a maximum output power of 4.4 W at 1228 nm with a beam quality factor (M2) of 1.4 and diode-to-Stokes conversion efficiency of 14.2%. Via tuning of the SDL oscillation wavelength, the diamond Raman laser was tuned from 1209 to 1256 nm, with output power exceeding 4 W over a 10-nm range. The evolution of the emission spectra and beam quality of both the SDL and the Raman laser have been investigated for different pump powers, revealing the onset of spectral broadening and beam “clean-up” effects with increasing power. The SDL spectral linewidth and beam overlap are then taken into account in calculations of the efficiency of the Raman laser. Using intracavity frequency-doubling in lithium triborate (LBO) within the Raman laser, up to 1.5-W output power at orange wavelengths was achieved with M2 <; 1.3 and linewidth ~0.1 nm full-width at half-maximum. Tuning of the visible emission was achieved via tuning of the SDL and temperature control of the LBO and covered the range 604.5-619.5 nm.

Two-octave polarized supercontinuum generated from a Q-switched laser pumped doubly resonant parametric oscillator

We report broadband polarized supercontinuum generated from a doubly resonant parametric oscillator with a lithium triborate gain crystal installed in a noncritical phase-matching condition. The parametric oscillator is pumped by a Q-switched frequency-doubled Nd:YAG laser at a repetition rate of 20Hz, producing a polarized spectrum with a width more than 324THz or a wavelength range between 0.6 and 1.7μm. The laser output is further extended to the blue part of spectrum via temperature-tuned second-harmonic generation in the same crystal.

Tunable femtosecond laser in the visible range with an intracavity frequency-doubled optical parametric oscillator

We demonstrated experimentally a synchronously pumped intracavity frequency-doubled femtosecond optical parametric oscillator (OPO) using a periodically-poled lithium niobate (PPLN) as the nonlinear material in combination with a lithium triborate (LBO) as the doubling crystal. A Kerr-lens-mode-locked (KLM) Ti:sapphire oscillator at the wavelength of 790 nm was used as the pump source, which was capable of generating pulses with a duration as short as 117 fs. A tunable femtosecond laser covering the 624–672 nm range was realized by conveniently adjusting the OPO cavity length. A maximum average output power of 260 mW in the visible range was obtained at the pump power of 2.2 W, with a typical pulse duration of 205 fs assuming a sech2 pulse profile.