Side-pumping Scheme Research Articles

Fresnel Lens Solar-Pumped Laser with Four Rods and Beam Merging Technique for Uniform and Stable Emission under Tracking Error Influence

Significant numerical improvements in Fresnel lens Nd:YAG solar laser collection efficiency, laser quality factors and tracking error compensation capacity by two Fresnel lenses as primary solar concentrators are reported here. A Nd:YAG four-rod side-pumping configuration was investigated. The four-rod side-pumping scheme consisted of two large aspherical lenses and four semi-cylindrical pump cavities, where the Nd:YAG laser rods were placed, enabling an efficient solar pumping of the laser crystals. A 104.4 W continuous-wave multimode solar laser power was achieved, corresponding to 29.7 W/m2 collection efficiency, which is 1.68 times that of the most efficient experimental Nd:YAG side-pumped solar laser scheme with heliostat–parabolic mirror systems. End-side-pumped configuration has led to the most efficient multimode solar lasers, but it may cause more prejudicial thermal effects, poor beam quality factors and a lack of access to both rod end-faces to optimize the resonant cavity parameters. In the present work, an eight-folding-mirror laser beam merging technique was applied, aiming to attain one laser emission from the four laser rods that consist of the four-rod side-pumping scheme with a higher brightness figure of merit. A 79.8 W multimode laser output power was achieved with this arrangement, corresponding to 22.7 W/m2. The brightness figure of merit was 0.14 W, being 1.6, 21.9 and 15.7 times that of previous experimental Nd:YAG solar lasers pumped by Fresnel lenses. A significant advance in tracking error tolerance was also numerically attained, leading to a 1.5 times enhancement in tracking error width at 10% laser power loss (TEW10%) compared to previous experimental results.

Multirod approach to enhance solar-to-laser conversion efficiency in the Odeillo solar furnace

A multirod solar laser station for the megawatt solar furnace (MWSF) in Odeillo, France, was conceptualized and numerically studied to improve the solar-to-laser power conversion efficiency. 18 heliostats from the 63-heliostat field were selected, and 347 kW of solar power was obtained at its focus. From there, a two-dimensional compound parabolic concentrator further concentrated and redistributed the solar rays toward 11 core-doped Nd:YAG rods, each fixed inside a fused silica flow tube. 11.40 kW of total multimode laser power was calculated, corresponding to a 3.29% solar-to-laser power conversion efficiency. This efficiency value represents an enhancement of 1.70 and 1.26 times over that attained from single-rod solar laser systems in side-pumping configuration tested in Odeillo, France, in which Nd:YAG rods were codoped with Cr3 + and Ce3 + ions, respectively. It was also 1.44 times higher than that obtained by a previously proposed side-pumping scheme with a solar flux homogenizer and 12 Nd:YAG rods for the same MWSF.

Improving side-pumped solar lasers using ring-array concentrators

ABSTRACT We report here a significant enhancement in side-pumped solar laser collection efficiency and solar-to-laser conversion efficiency by a ring-array primary concentrator. A single and a dual-rod side-pumping configuration were numerically investigated. In the former, a thick laser rod was pumped with the full collection area of the ring-array solar concentrator. In the latter, two thin laser rods were pumped simultaneously. 49.70 W continuous-wave multimode solar laser power, corresponding to 29.06 W/m2 collection efficiency, and 3.06% solar-to-laser power conversion efficiency were numerically attained for the dual-rod side-pumping scheme, being 1.65 and 1.26 times higher than the previous experimental records with Nd:YAG side-pumping configurations. A three-folding-scheme single laser beam technique is presented, enabling a significant improvement of laser beam quality factors.

Solar Pumped Lasers: High-Efficiency Multi-Pass Side Pumping Scheme with Fresnel Lens

A multi-pass side-pumping scheme for solar pumped Nd:YAG laser on 1 m diameter Fresnel lens is numerically analyzed. Using of the Monte Carlo photon-tracing numerical method, three different pumping schemes were studied. The results showed that a large efficiency improvement in a multi-pass side-pumping scheme compared to the double-pass side-pumping scheme. The study demonstrated that the multi-pass side-pumping scheme can double the overall efficiency of solar double-pass side-pumped Nd:YAG laser.

Thermo-Optic Numerical Research on Segmented Circular LD Arrays Side-Pumping a Nd:YAG Laser Rod

The configuration designs of the laser diode (LD) side-pumping laser rods focus on how to solve the space conflict between the pump and heat-removal devices because both want to use the larger lateral surface of the laser rod. The conflict is better balanced in the three different side-pumping geometries: the segmented circular LD array side-pumping configuration, the annular liquid-cooling structure, and the compensated semicircular LD array side-pumping arrangement. The temperature distributions and thermo-optic effects of the laser rod in the segmented circular LD array side-pumping configuration are analyzed in contrast with those in the other arrangements. The numerical results indicate that the periodical segment-pumping scheme provides higher beam quality than the compensated semicircular side-pumping scheme, enabling removal of the complex liquid cooling system in medium-power applications, thus showing the potential to be used in compact and miniature laser systems.

A Simple Multi-Pass Side-Pumping Scheme for Solar Powered Lasers

The new multi-pass configuration of side-pumped Nd:YAG solar laser for enhancement of conversion efficiency is studied by computer simulation of the laser system. The active medium in the form of a slab providing effective heat dissipation during side pumping by concentrated solar radiation at the focus of a parabolic concentrator with a diameter of 1 m is considered. It is shown that multi-pass configuration doubles the output laser power.

Side-pumped continuous-wave Nd:YAG solar laser with 5.4% slope efficiency

The authors report here a significant progress in side-pumped solar laser slope efficiency by pumping a 3.0 mm diameter, 30 mm length Nd:YAG single-crystal laser rod through a heliostat-parabolic mirror solar energy collection and concentration system with 0.9 m2 effective collection area. A large fused silica aspheric lens allowed an efficient focusing of the concentrated solar power from the focal zone of the parabolic mirror into the laser rod mounted within a novel two-dimensional semi-cylindrical pump cavity. 15.3 W continuous-wave 1064 nm solar laser power was measured, resulting in 5.40% slope efficiency and 2.43% solar-to-laser conversion efficency, being 2.08 and 2.30 times, respectively, more than the previous records by side-pumping configuration. The 5.40% slope efficiency is also 1.08 times more than the previous record with Nd:YAG single-crystal rod by end-side-pumping approach. By adopting an asymmetric laser resonator, this novel side-pumping scheme also enabled an efficient production of high-quality solar laser beams in either TEM11 (4.0 W), TEM01* (doughnut-shaped, 2.9 W), TEM10 (3.2 W) or TEM00 (2.8 W) mode profiles.

Total internal reflection-based side-pumping configuration for terawatt ultraviolet amplifier and laser oscillator development

A two-side-pumping scheme that is based on total internal reflection in a diamond-cut Ce3+:LiCaAlF6 crystal suitable for the development of an ultraviolet laser and femtosecond amplifier system is proposed. Experimental fluorescence images and lasing results that demonstrate total internal reflection of the excitation beam using this diamond-cut crystal are presented. Calculations for the optimized crystal geometry that facilitate high extraction efficiency and homogeneity of the absorbed excitation beam are also discussed. About 50% increase in extraction efficiency compared to previously reported chirped-pulse femtosecond ultraviolet amplifier operating at 50-GW peak power is expected using this total internal reflection-based two-side-pumping configuration and a diamond-cut Ce3+:LiCaAlF6 crystal with a geometry of $${\phi _1}$$ = 103°, $${\phi _2}$$ = $${\phi _4}$$ = 82°, $${\phi _3}$$ = 93°, a length of 1.23 cm, a height of 2 cm, and an absorption coefficient of ~ 1.5 cm−1. Our results can be used as a guide during the crystal growth process by providing the appropriate crystal geometry and size for a particular absorption coefficient to achieve high extraction efficiency. With the appropriate crystal combined with multiple-beam pumping afforded by the side-pumping scheme, the development of an all-solid-state ultraviolet laser operating at terawatt level would be within reach.

High-energy diode side-pumped Er:LiYF4 laser.

This work presents a novel diode side-pumping scheme for Er:YLF with a characteristic laser emission at 2.81μm. Average output powers greater than 10W and corresponding pulse energies exceeding 100mJ with a high slope efficiency of 18.7% are achieved. The Er:YLF laser efficiently operates at room-temperature cooling water and maintains a good beam quality of M2<12 in the major axis and M2<6 in the minor axis of the beam profile. The laser cavity is studied by means of Findlay-Clay analysis, and the operation at characteristic pump parameters is investigated. In addition, a dynamic laser rate equation simulation is introduced for quantitative and qualitative comparison. This compact and scalable free-running Er:YLF laser provides an effective building block for a subsequent Q-switching concept.

Distributed and Side-Pumped Fiber Laser Using a Laser Diode Bar Stack

A distributed, side-pumped Yb3+-doped fiber laser is demonstrated using a laser diode stack as a pump source. Four subwavelength gratings fabricated on the same fused-silica substrate were aligned with four laser diode bars of the laser diode stack package for coupling pump light into double-clad fibers. Under the 975-nm pump power of 124.6 W, a 58 W Yb3+-doped fiber laser has been demonstrated. Due to the distributed pumping scheme, the nonuniformity of fiber heating from quantum defect is reduced as seen from the narrow linewidth of the fiber laser output across the entire pump power range. As a further step, the genetic algorithm method was used to design an aperiodic grating with a 40-nm fine structure. The adoption of the aperiodic grating, fabricated by using the E-beam lithography process, reduced the edge coupling loss effect, which allowed to reach 70% coupling efficiency. The side pumping scheme is compact and efficient, and power scaling is possible with more laser diode bars in the laser diode bar stacks. To the best of our knowledge, this is the first demonstration of a distributed pumped fiber laser using a laser diode bar stack as the pump source.

Laser diode side-pumped Nd:YVO4 microchip laser with film-etched microcavity mirrors.

Microchip lasers are applied as the light sources on various occasions with the end-pumping scheme. However, the vibration, the temperature drift, or the mechanical deformation of the pumping light in laser diodes in the end-pumping scheme will lead to instability in the microchip laser output, which causes errors and malfunctioning in the optic systems. In this paper, the side-pumping scheme is applied for improving the disturbance-resisting ability of the microchip laser. The transverse mode and the frequency purity of the laser output are tested. To ensure unicity in the frequency of the laser output, numerical simulations based on Fresnel-Kirchhoff diffraction theory are conducted on the parameters of the microchip laser cavity. Film-etching technique is applied to restrain the area of the film and form the microcavity mirrors. The laser output with microcavity mirrors is ensured to be in single frequency and with good beam quality, which is significant in the applications of microchip lasers as the light sources in optical systems.

A simplified hollow-core microstructured optical fibre laser with microring resonators and strong radial emission

A simplified hollow-core microstructured optical fibre (SHMOF) laser with microring resonators and strong radial emission is demonstrated. We propose that a submicron thickness silica ring embedded in the SHMOF can act as a microring resonator, with the advantages of being both compact and solid. Furthermore, the microfluidics can be easily controlled with a side pumping scheme. We also obtained a highly stable and tunable laser. The attractive possibility of developing microfluidic dye lasers within single SHMOFs presents opportunities for integrated optics applications and biomedical analysis.

Polarization characteristics of Whispering-Gallery-Mode fiber lasers based on evanescent-wave-coupled gain

The polarization characteristics of Whispering-Gallery-Mode (WGM) fiber lasers based on evanescent-wave-coupled gain are investigated. For the laser gain is excited by side-pumping scheme, it is found that the polarization property of lasing emission is simply dependent on the polarized states of the pump beams. The polarization property of lasing emission depends on the propagating situation of the pump beams in an optical fiber if the laser gain is excited by evanescent-wave pumping scheme, that is, if the pump beams within the fiber are meridional beams, the lasing emission is a transverse electric (TE) wave that forms a special radial polarization emission. However, if the pump beams within the fiber are skew beams, both transverse magnetic (TM) and TE waves exist simultaneously in lasing emission that forms a special axially and radially mixed polarization emission. Pumped by skew beams, the wave-number differences between TE and TM waves are also investigated quantitatively, the results demonstrate that the wave-number difference decreases with the increase of the fiber diameter and the refractive index (RI) of the cladding solution. The observed polarization characteristics have been well explained based on lasing radiation mechanism of WGM fiber laser of gain coupled by evanescent wave.

Theoretical study of pumping absorption in a co-linear side-pumping coupler

The coupling and absorption properties of a co-linear side-pumping scheme have been calculated numerically by the Beam Propagation Method. In the co-linear side-pumping scheme which is composed of a multi-mode pump fiber and a core-doped double-cladding fiber, the coupling and absorption properties of each incident mode are different, and the absorption efficiency of the pump light depends on power distributions of the launched modes. We got higher absorption efficiency when high-order mode has bigger power percentage in total input light. Compared with the end-pumping scheme, co-linear side-pumping needs bigger absorption coefficient to reach high pump light absorption efficiency.

Test of spectral emission and absorption characteristics of active optical fibers by direct side pumping

Emission and absorption are two main properties of active optical fibers that are important for fiber amplifiers and lasers. We propose a direct side pumping scheme for non-deconstructive evaluation of active optical fibers. This scheme enables a simple in situ test of both emission and absorption characteristics without cutting fiber and produces good accuracy with very low pumping background. A commercial Er-doped fiber and a home-made Bi/Er co-doped optical fiber have been tested to demonstrate that the scheme is a useful alternative technique for characterizing active optical fiber or waveguides.

Transverse mode competition in gain-guided index antiguided fiber lasers

Single-mode laser action has been reported previously in a gain-guided, index antiguided fiber using a scalable side pumping scheme. In this paper we demonstrate the role of transverse mode competition on laser oscillation in such a fiber laser. It enables single, lowest-order mode lasing with a beam quality of M2&lt;2 when using a combination of large fiber core radius and low output coupler reflectivity previously considered to rule out gain-guided index antiguided lasing with such beam quality. In addition, the larger core radii fibers and low output coupler reflectivity enables improved slope efficiency. Both theoretical analysis and experimental results are presented demonstrating mode competition governed lasing in a gain-guided, index antiguided fiber.

Scalable side-pumped, gain-guided index-antiguided fiber laser

Single-mode laser action has been demonstrated in a gain-guided, index-antiguided (GG IAG) Nd3+ doped phosphate glass fiber through the use of a diode side-pumping scheme. This pump technique can allow for length scaling of diode-pumped GG IAG fibers and therefore true power scaling of the GG IAG concept. Near-Gaussian beam quality was demonstrated with beam M2 of 1.4.

Amplification of Ultraviolet Femtosecond Pulse by a Micro-Pulling Down Method-Grown Ce:LiCAF Crystal in a Prismatic Cell-Type, Side-Pumping Configuration

We propose an efficient side-pumping scheme for ultraviolet (UV) femtosecond pulse amplification in micro-pulling-down (µPD) method-grown Ce:LiCAF using a prismatic cell-type configuration. By uniformly illuminating four sides of a 2-mm-diameter and 30-mm-length Brewster-cut, nearly as-grown crystal, the risk of damage is dramatically reduced. Without using a chirp pulse amplifier scheme, UV femtosecond pulse at 290 nm is amplified 4 times with no significant increase to its pulse duration and B-integral. Our results show that a laser-quality, Ce:LiCAF crystal, efficiently grown by the µPD method and pumped in a prismatic-cell type configuration paves new possibilities in providing high energy UV femtosecond pulses.

Side pumping scheme with a dual-sided grating coupler

A robust dual-sided grating coupler with high coupling efficiency (CE) is proposed and rigorously analyzed for laser-diode (LD) bars side pumping double-clad fiber (DCF). It consists of a double-groove metal grating and a composite diffraction grating with dielectric–metaldielectric (DMD) sandwich structure placed behind the upside and downside of the inner-cladding of the DCF respectively. High coupling efficiencies are obtained when the incident pump light is TE-polarized (85.96%), TM-polarized (90.7%) and un-polarized (76.04%) respectively. It is also demonstrated that the coupler is tolerant to potential fabrication errors and variations of the incident angle and central pump wavelength.

Multi-point side pumping scheme of fiber lasers for high-power diode arrays

A multi-point side pumping scheme of double-clad fiber lasers was presented for high-power diode arrays. It made use of multiple dielectric transmission gratings to realize high coupling efficiency and low pump light leakage ratio simultaneously. Appropriate material and practical structural parameters of the transmission gratings were chosen and designed by using a rigorous Eigen-mode theory combined with a genetic algorithm (GA) and a quasi-Newton method. The GA provided initial parameter values for the quasi-Newton method to get the final optimal results. For TE-polarized pump lights, a perfect transmission grating structure was found for side pumping and the coupling efficiency (CE) of 98% can be achieved. Meanwhile, the CE is 83% for TM-polarized pump lights. And the leakage ratios of the pump lights were only 11.3% and 4.9% for TE- and TM-polarized when a multi-point side pumping scheme was adopted.