Ceramic Laser Research Articles

Passively Q-switched and broadly tunable continuous-wave operations of a 2-μm Tm3+:Lu2O3 ceramic laser upconversion pumped at 1.064 μm

We report passively Q-switched and broadly tunable continuous-wave operations of a trivalent thulium ion-doped Lu2O3 ceramic laser near 2 μm by employing upconversion pumping at 1 μm. Upconversion pumping was performed with a commercial 1064-nm Yb:fiber laser and nonlinear absorption of up to 41 % was obtained. In the continuous wave case, a four-mirror x-cavity generated as high as 257 mW of output power at 2.06 μm with a power slope efficiency of 12 % with respect to the incident pump power. Tuning performance was further investigated with a quartz birefringent tuning plate and broad, continuous tuning was obtained in the 1950–2090 nm wavelength range. In addition, passively Q-switched operation was demonstrated with a semiconductor saturable absorber, yielding stable, 4.15-μs-long pulses at the pulse repetition frequency of 28.8 kHz.

The removal of three kinds of occlusal veneers by Er: Yag laser.

This study aimed to remove occlusal veneers of varied thicknesses and compositions by Er:Yag laser in vitro and analyze the interfacial microstructure between veneers and tooth that irradiated by laser, by which experimental evidence could be provided to support the non-invasive removal of occlusal veneerby laser. Fresh mandibular premolars extracted for orthodontic requirements were collected for tooth preparation. Three kinds of ceramic materials (Vita Suprinity, Vita Mark Ⅱ, and Upcera Hyramic) were selected to fabricate occlusal veneer with different thicknesses (1.0, 1.5, and 2.0 mm). One week later, Er:Yag laser (2.5 W and 3.5 W) was used to irradiate and remove the occlusal veneer and recorded the timespan. After the removal operation, the micro-morphologies of samples were examined by scanning electron microscope. Upcera Hyramic veneer failed to be removed (>20 min); the operation span at 2.5 W, Vita Suprinity (96.0 s±16.0 s) was longer than Vita MarkⅡ(84.5 s±19.5 s) in the 1.0 mm group (P<0.05), and Vita Suprinity (246.5 s±13.5 s) was longer than Vita MarkⅡ(170.0 s±14.0 s) in the 1.5 mm group (P<0.05). At 3.5 W, Vita Suprinity (381.0 s±24.0 s) was longer than Vita MarkⅡ(341.5 s±26.5 s) in the 2.0 mm group. Increasing laser power could shorten the operation span and facilitate the removal of occlusal veneers with the same thickness and composition. The occlusal veneer was sustained when insufficient laser power was applied. With the same laser power and ceramic thickness, laser penetration could interfere with the integral of the ceramic structure when the laser interacted with the bonding layer. With the same ceramic composition and laser power, the operation span and laser power increased with the thickness of the occlusal veneer. However, the laser was incapable of removing occlusal resin veneer directly.

Reduction of depolarization loss in a Tm-doped sesquioxide ceramic laser using a ring-shaped pump beam.

We report on a simple method for reduction of the depolarization loss in an end-pumped Tm:Y2O3 ceramic laser by using a near-field ring-shaped pump beam. Initially, we theoretically derive the expression of the depolarization loss in a bulk laser end-pumped with a near-field flat-top-hat or ring-shaped beam, where a significant reduction of depolarization loss in the latter case is presented. Experimental verification is thereafter carried out with a Tm:Y2O3 ceramic laser employing these two different pump configurations. It shows that the experimentally measured depolarization losses are close to the simulated values; the loss in the case of the annular-beam pump is almost 18 times lower than that with a quasi-top-hat beam at a same absorption pump power of 7.4 W. This work, as a proof-of-principle study, indicates that depolarization loss in the end-pumped bulk lasers can be significantly reduced simply by using a ring-shaped pump beam.

Highly efficient lasing and thermal properties of Tm:Y2O3 and Tm:(Y,Sc)2O3 ceramics.

We report on thermal, spectroscopic, and laser properties of transparent 5 at.% Tm3+-doped yttria and "mixed" yttria-scandia ceramics fabricated by vacuum sintering at 1750°C using nanoparticles produced by laser ablation. The solid-solution (Tm0.05Y0.698Sc0.252)2O3 ceramic features a broadband emission extending up to 2.3 µm (gain bandwidth, 167 nm) and high thermal conductivity of 4.48 W m-1 K-1. A Tm:Y2O3 ceramic laser generated 812 mW at 2.05 µm with a slope efficiency η of 70.2%. For the Tm:(Y,Sc)2O3 ceramic, the output power was 523 mW at 2.09 µm with η = 44.7%. These results represent record-high slope efficiencies for any parent or "mixed" Tm3+-doped sesquioxide ceramics.

High Power (~10 kW) Yb:YAG Ceramic Slab Laser Operating at 1030 nm

A high power quasi-continuous-wave (QCW) efficiently-cooled ceramic slab laser oscillator is reported. The maximum output power can reach 9.85 kW with the optical-to-optical efficiency of 60% with respect to the absorbed pump power as well as the slope efficiency up to 65.3%. To the best of our knowledge, this is the highest output power for any Yb:YAG ceramic laser oscillator. Beam aberration of the efficiently-cooled Yb:YAG ceramic slab laser is detected by a parallel probe beam along the optical path of laser beam. The peak-to-valley (PV) value of the wavefront distortion is 2.8 μm under full output power. The beam quality factor β is estimated to be about 3.7 times diffraction limit while without additional correction system. A numerical model of temperature field is constructed to analyze the wavefront distortion of the probe beam, and the calculated results are in agreement with the experimental data.

A Review of Cr2+ or Fe2+ Ion-Doped Zinc Sulfide and Zinc Selenide Ceramics as IR Laser Active Media

Zinc chalcogenides doped with Cr2+ or Fe2+ ions are of considerable interest as active media for IR lasers operating in the 2–5 µm wavelength range. Such lasers are in demand in various fields of medicine, remote sensing and atmospheric monitoring, ranging, optical communication systems, and military applications. In recent years, however, the rate of improvement in the characteristics of zinc chalcogenide laser sources has slowed considerably. Unwanted thermally induced effects, parasitic oscillations, and laser-induced damage of the active element have hindered the scaling of output power and efficiency. However, the physical and chemical properties of the materials leave ample room for further improvements. In particular, the control of the dopant concentration profile in the active element is of great importance. Zero concentration of Cr2+ or Fe2+ ions on the radiation input/output surfaces can significantly increase the laser-induced damage threshold; the designed concentration distribution in the element volume allows regulation of heat dissipation and reduction of parasitic oscillations. The zinc chalcogenide ceramic technology seems to be the most suitable to solve this challenge. This review presents and discusses the state of the art in ZnS and ZnSe optical and laser ceramics and the directions for further development of their technology.

Microstructure and properties characterization of Yb:Lu2O3 transparent ceramics from co‐precipitated nano‐powders

Abstract5at.% Yb:Lu2O3 transparent ceramics were fabricated successfully by vacuum sintering along with hot isostatic pressing posttreatment from the nanopowders. The influences of calcination temperature on morphology and microstructures of powders and ceramics were studied systematically. The optimal ceramic sample from the nanopowder calcined at 1050°C shows uniform and dense microstructure with the in‐line transmittance of 81.5% at 1100 nm. The results of the thermal measurements, that is, thermal conductivity and specific heat, were related to the changes occurring in the microstructure of the ceramics studied. It was shown on this basis that appropriate control of the technological process of sintering ceramics makes it possible to obtain laser ceramics with very good thermal properties as well as maintaining their high optical quality. Concerning the laser performance, the highest‐optical quality 5at.% Yb:Lu2O3 sample was pumped in quasi‐continuous wave conditions measuring a maximum output power of 2.59 W with a corresponding slope efficiency of 32.4%.

Nickel–cobalt layered double hydroxide saturable absorber for a mid-infrared 2 µm Tm:YAG ceramic mode-locked laser

Nickel–cobalt layered double hydroxide saturable absorber for a mid-infrared 2 µm Tm:YAG ceramic mode-locked laser

Passively Q‐switched Tm:YAG ceramic laser with TiS2 saturable absorber

AbstractA two‐dimensional titanium disulfide (TiS2) nanosheet film is prepared on a YAG crystal substrate. The saturated absorption behavior of TiS2 on the YAG substrate is investigated. Then, TiS2 is successfully employed as a modulation element to develop a Tm:YAG ceramic eye‐safe pulsed laser. With a 7.04 W absorbed pump light and a 3% transmission of output coupler, the greatest average optical power, and the least pulse width (PD) are 233 mW and 524 ns, separately. The pulse repeated frequency of 69 kHz is generated, while the single pulse energy (SPE) is 3.38 µJ. Based on the experimental results, TiS2 nanosheet films possess the practical value as saturable absorbers for 2.0 μm eye‐safe pulsed lasers.

Assessment of possible performances of compact solar-pumped lasers using transparent Cr3+, Nd3+-co-doped YAG ceramics micro rods

Employing a commercially available off-axis parabolic mirror of ⌀50.8 or ⌀76. 2 mm caliber and ⌀1 or 1 × 1 × 10 mm Cr3+, Nd3+-co-doped YAG ceramic micro laser medium (LM), our compact solar-pumped lasers (μSPL) could oscillate continuously without any forced air cooling from 11:00 a.m. beyond 5:30 p.m. tracking the sun outdoors. However, their energy conversion efficiencies ηpower have not exceeded so far 1%. Numerical assessments of μSPL performance using a fundamental expression of laser oscillation based on experimentally obtained parameters were performed. Dependences of ηpower on transmittance of an output coupler, mode-matching efficiency ηmode, length of LM, distributed loss constant in LM, and Cr content as well as the necessity of the concentration ratio as high as 10,000 were elucidated. The values of ηmode between 0.3 and 0.5 coming from the present confocal resonator roughly reproduced ηpower around 1%. Based on the assessments, possible approaches for further improvement of μSPL performance were evaluated including employment of composite LM to increase ηmode.

Synergistic Strengthening Mechanisms of Dual-Phase (TiN+AlN) Reinforced Aluminum Matrix Composites Prepared by Laser Powder Bed Fusion.

Dual-phase reinforcing approach provides a novel and efficient strategy for the fabrication of advanced aluminum matrix composites (AMCs). The devisable and desirable performance could be achieved by tuning dual-phase reinforcing system. However, it is still challenging to design a dual-phase reinforcing system with synergistic strengthening effect, especially for the laser powder bed fusion (LPBF) characterized by nonequilibrium metallurgical process. In this work, we designed and fabricated dual-phase (TiN+AlN) particles (20 wt.%) reinforced pure Al by LPBF. The TiN and AlN can form a metastable ternary Ti1-xAlxN solid solution in the whole range of composition, which is a promising reinforcing phase for AMCs. We observed novel microstructure in laser-fabricated composites under the action of dual-phase (TiN+AlN) ceramic particles and laser melting process. A gradient layer is formed on the surface of TiN particles. This interfacial structure can act as an anchor for ceramic particles in the Al matrix, which is beneficial to achieve a strong interface bonding and good load transfer. Besides this gradient layer, uniformly dispersed Ti1-xAlxN nanoparticles were observed to precipitate, which can effectively hinder dislocation movement and refine grains. Furthermore, the pure Al and TiN/Al, AlN/Al composites were fabricated to compare and reveal the contributions of dual-phase (TiN+AlN) reinforcements. The tensile strength of the (TiN+AlN)/Al composite reach ∼254 MPa, improved by ∼75% and ∼81% compared with those of the TiN/Al and the AlN/Al composites, respectively. This novel microstructure about gradient layer and precipitated nanoparticles contributes to the high strengthening efficiency of the (TiN+AlN)/Al composite.

High power Ho:Y2O3 ceramic laser with controllable output intensity profile at 2.1 µm.

We report on a high-power Ho:Y2O3 ceramic laser at 2.1 µm with controllable output beam profile ranging from LG01 donut, flat-top to TEM00 mode using a simple two-mirror resonator. In-band pumped at 1943nm using a Tm fiber laser beam shaped via a coupling optics comprising a capillary fiber and lens-combination to achieve distributed pump absorption in Ho:Y2O3 and hence selective excitation of the target mode, the laser yields 29.7 W of LG01 donut, 28.0 W of crater-like, 27.7 W of flat-top and 33.5 W of TEM00 mode output for absorbed pump power of 53.5 W, 56.2 W, 57.3 W and 58.2 W, respectively, corresponding to a slope efficiency of 58.5%, 54.3%, 53.8% and 61.2%. This is, to the best of our knowledge, the first demonstration of laser generation with continuously tunable output intensity profile at ∼2 µm wavelength region.

Self-Q-switched and widely tunable continuous-wave operation of a Tm3+:Lu2O3 ceramic laser near 2 μm

We report, for the first time to our knowledge, self-Q-switched (SQS) operation of a Tm3+:Lu2O3 ceramic laser near 2 μm based on the 3F4→3H6 optical transition. By careful optimization of cavity focusing, SQS operation could be achieved at several curved mirror separations without any external modulator and the laser delivered 9.7-μs pulses at the wavelength of 2091 nm with a pulse repetition rate of 26 kHz. In the experiments, a tight-focusing resonator design was further employed to achieve low-threshold continuous-wave (CW) operation of the laser with lasing threshold pump powers as low as 33 mW. With an incident pump power of 590 mW at 776 nm, a maximum output power of 164 mW was obtained at 2097 nm with a slope efficiency of 30% with respect to the incident pump power. The tuning range of the CW Tm3+:Lu2O3 ceramic laser could be extended up to the wavelength of 2235 nm.

Direct Kerr-lens mode-locked Tm: LuYO3 ceramics laser

Abstract A direct Kerr-lens mode-locked Tm: LuYO3 ceramics laser without the aid of any mode-locked starting element is reported for the first time. The pulse duration as short as 259 fs and maximum average output power of 326 mW are obtained at a repetition rate of 97.1 MHz. The corresponding optical spectrum centered at 2053 nm exhibits a bandwidth of 19.8 nm, which indicates the presence of nearly Fourier transform-limited pulses. Such a Kerr-lens mode-locked Tm: LuYO3 ceramics laser is a promising ultrashort pulse source, with both the excellent laser characteristics of Tm: LuYO3 and the high-power 790 nm LD pumping scheme.

Mid-infrared laser operation of (Er0.07La0.10Y0.83)2O3 sesquioxide ceramic

A transparent sesquioxide ceramic (Er0.07La0.10Y0.83)2O3 was fabricated by vacuum sintering at 1780 °C for 3 h with lanthana acting as a sintering additive. It was of single-phase nature (sp. gr. Ia ) with a close-packed microstructure (average grain size: 17 μm, pore content: 5 ppmv) and high transparency of 80% at 1.1 μm. The La3+ ions induced additional inhomogeneous broadening in the absorption and emission spectra of Er3+ ions. For the 4I11/2→4I13/2 transition, the stimulated-emission cross-section σ SE was 1.06 × 10−20 cm2 at 2719 nm and the luminescence lifetimes of the 4I11/2/4I13/2 states amounted to 2.73/5.91 ms, respectively. A (Er0.07La0.10Y0.83)2O3 ceramic laser generated 300 mW at 2840 nm with a slope efficiency of 27.7% and a laser threshold of only 17 mW.

Effect of sintering additives on Y2O3 ceramic: Synthesis, structural, morphological, and optical properties investigations

Solid-state ceramic lasers have a wide range of applications in industrial, medical, and military applications. This research work presents the fabrication of vacuum sintered Y2O3 ceramics synthesized using co-precipitation method. The impact of sintering additives such as La2O3 and ZrO2 were examined on the structural and morphological traits of Y2O3. The development of pure cubic phases is revealed by X-ray diffraction studies. Williamson-Hall method is used to determine the crystallite size and micro-strain. The incorporation of La3+ and Zr4+ are confirmed through FTIR spectra. The optical characteristics are investigated through UV–VIS spectroscopy. The addition of La3+ and Zr4+ additives increases the densification of Y2O3 ceramic pellets and improves their sintering behavior. The effect of sintering additives on grain size and elemental composition were examined using scanning electron microscopy and energy dispersive spectroscopy.

Fabrication and properties of novel composite laser ceramics with a surface‐gain structure

AbstractTo suppress heat effects in a high‐power laser system, it has been proposed to use a few composite laser gain media to improve the heat management ability. The surface‐gain structure has the advantages of both slab and thin‐disk configurations, which has huge potential in high‐power laser. For the first time, novel composite laser ceramics with surface‐gain structure have been fabricated by tape casting and sintering technology. The in‐line transmittances of surface‐gain ceramics in 1100 and 400 nm are 83.5% and 79.1%, respectively. According to the laser ablation–coupled plasma mass spectrometry, the diffusion distance of Yb3+is about 150 µm. The laser experiment yields a low repetition rate pulse of 1.9 J with a pump absorption energy of 11 J and an optical‐to‐optical conversion efficiency of 17.2%.

High-power Er:Y2O3 ceramic laser with an optical vortex beam output at ∼ 2.7 μm

We report on the direct generation of the high-power optical vortices at ∼2.7 μm from an Er:Y2O3 ceramic laser end-pumped by an annular pump beam using a simple capillary fiber-based pump beam conditioning scheme. Taking advantage of the thermal gradient on the gain medium and mode matching between the pump and oscillating modes, vortex beams with a controllable topological charge order of l = 1 and l = 2 were successfully achieved. The laser yields 4.65 W of output power at an absorbed power of 19.8 W, corresponding to a slope efficiency of 25.9% with respect to the absorbed pump power. Adaptable beam profiles from a shallow crater-shape to quasi-top-hat intensity patterns were directly produced by actively defining the gain distribution in the ceramic, generating 4-W shallow crater-shape beams and 3.9-W quasi-top-hat beams, corresponding to a slope efficiency of 22.0% and 22.7%, respectively. Such optical vortices and tailored spatial intensity profiles in the 3-µm spectral region will enable novel applications, such as super-resolution molecular spectroscopy and material processing.

Single Longitudinal Mode and Widely Tunable Er:Y2O3 Ceramic Laser at ∼ 2.7 μm

We report on single-longitudinal-mode and tunable operation of an Er:Y <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sub> O <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> ceramic laser at ∼2.7 μm using intracavity Fabry-Perot etalons combined with a birefringent filter. The laser is pumped with a high brightness, narrow linewidth diode source at ∼980 nm and generated over 240 mW of linearly polarized output power at 2717 nm for an absorbed pump power of 5.1 W. The wavelength tuning range demonstrated was spanned from 2708.6 nm–2741.2 nm, with output powers of >220 mW in the whole tuning range.

Formation mechanism and quantitative analysis of pores in Al2O3–ZrO2 ceramic different structures by laser additive manufacturing

Pores is one of the most defects during laser additive manufacturing of ceramic material. In this paper, different structures of Al2O3–ZrO2 ceramics are deposited by using powder-feeding laser additive manufacturing. The ceramic structures can be simplified into three typical structures: linear-type, face-type and body-type structure. The formation mechanism and quantitative analysis of pores in different ceramic structures are studied. The pores of ceramic structure is mainly divided into four types: intercrystalline pore, interlayer pore, intralayer pore and shrinkage pore. In the linear-type structure, the number of pores with the interval 0–1000 μm2 accounts for 98.8%, while the area of pores with the interval above 104 μm2 accounts for 58.33%. The remelting rate of deposition layer has great influence on the pores. The Marangoni convection changed from inflow mode to outflow mode, which leads to that bubbles have easily escape from molten pool. In the face-type structure, the number and area of pores at the interval 0–1000 μm2 account for 98.96% and 51.62%, respectively. Overlap ratio is the key factor affecting pore. Under the effects of the Marangoni convection and the overlap of deposition layer, the irregular pores are easily formed in the bottom of overlap region of deposition layer. The pores characteristic in the body-type structure is similar to that in linear-type structure. Due to the laser remelting and overlap phenomenon, the thermal accumulation effect is more obvious in the short time interval and continuous deposition process of body-type structure. Thus, the gas of molten pool can be easily escaped. This study can provide the theoretical basis for the suppression of pores in ceramic laser additive manufacturing.