980-nm Laser Research Articles

Multiple increase in the radiative efficiency of 1060-nm laser diodes based on heterostructures with tunnel-coupled injection and a single waveguide mode.

An approach aimed at increasing the radiative efficiency in heterostructures operating in a single vertical mode at 1060 nm has been studied. Two types of heterostructures-the STJH (single tunnel junction heterostructure) and DTJH (double tunnel junction heterostructure)-have been developed to obtain the operation of a single waveguide mode of the first and second order, respectively. A multiple increase in the injection efficiency is realized by using tunnel junctions (TJs) embedded in the wide-gap barriers and placed between the active regions. An internal quantum efficiency of close to 100% and a transparency current density of 78 A/cm2 is demonstrated for both types of heterostructures, while the internal optical loss is 5.2 and 3.8 cm-1 for STJH and DTJH, respectively. The maximum radiative efficiency (for the initial linear part of the light-current curve) and the output optical power (for the current pulse of 1 µs and 9.6 A) reach 1.6 W/A and 7.8 W for STJH and 2.2 W/A and 15.8 W for DTJH.

Effect of photodynamic therapy as an adjunctive to mechanical debridement on the nonsurgical treatment of peri-implant mucositis: A randomized controlled clinical trial

The use of photodynamic therapy (PDT) has been evaluated as an adjunctive technique for bacterial decontamination of implants with peri-implantitis. Given the controversies over the efficacy of the application of PDT to treat peri-implant diseases, the present clinical study aimed to evaluate the posttherapeutic clinical parameters and cytokine levels in peri-implant crevicular fluid in patients with peri-implant mucosal inflammation, receiving mechanical debridement (MD) alone or in association with PDT. In this double-blinded randomized clinical trial, 52 patients with peri-implant mucosal inflammation were selected and they were randomly assigned to 2 treatment groups: a MD group and an MD + PDT group using an 805 nm laser and indocyanine green (ICG). Although the decrease in bleeding on probing was the primary outcome, pocket depth, PUS, pain on probing, clinical attachment level, gingival recession, tumor necrosis factor-α, interleukin (IL)-1β, IL-6 and matrix metalloproteinase-8 were also evaluated at baseline, 2-week, and 3-month postintervention. Repeated measure analysis of variance was used to analyze inter-group differences and a P ≤ 0.05 was considered for significant differences between tested parameters. Statistically significant improvements (P < 0.001) were detected for all variables after comparison of baseline data with those collected at each time interval of the study. Nevertheless, the inter-group comparisons of these variables between the baseline, 2-week, and 3-month intervals did not reveal any significant decrease in sites treated with either MD alone or MD + PDT. The application of PDT using 805-nm laser and ICG as an adjunct therapy to MD did not provide any additional improvements in the clinical or biologic parameters of peri-implant mucosal inflammation.

Ellipticity properties of symmetric molecules &lt;inline-formula&gt;&lt;tex-math id="M2"&gt;\begin{document}$ {\text{H}}_{\text{2}}^ + $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M2.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M2.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; in strong and short-wavelength laser fields

Ellipticity properties of high-order harmonic generation (HHG) from symmetric molecules &lt;inline-formula&gt;&lt;tex-math id="M6"&gt;\begin{document}$ {\text{H}}_{\text{2}}^ + $\end{document}&lt;/tex-math&gt;&lt;alternatives&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M6.jpg"/&gt;&lt;graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="4-20221946_M6.png"/&gt;&lt;/alternatives&gt;&lt;/inline-formula&gt; in strong and short wavelength (less than 800nm) laser fields are numerically investigated. In this study, the ellipticity of harmonic is compared with the corresponding harmonic spectrum and dipole, and the calculation results are analyzed and the results obtained at different laser intensities, different laser wavelengths, different internuclear distances and different orientation angles are compared with each other. Our numerical simulations show that the influences of laser intensity, laser wavelength, internuclear distance and orientation angle on the ellipticity of harmonic are different. Especially in a two-center interference region, the excited state plays an important role in the HHG, but the effects of the excited state on the ellipticity of harmonic are different at different orientation angles. Further analysis shows that these different effects are due to the influence of the excited state on the harmonic yield. Using the numerical scheme, it is determined that in the two-center interference region, the excited state plays an important role in the parallel harmonic spectrum, while the effects of the excited state on the perpendicular harmonics at different angles are all very small, which results in different phase differences between the accurate harmonic spectrum and the harmonic spectrum only returning to the ground state. Overall, the relative yields of the accurate perpendicular harmonics are lower (higher) than those of the accurate parallel harmonics, but the intensities of the perpendicular harmonics, which only return to the ground state, are comparable to (or farther away from) those of the parallel harmonics which are only to return to ground state in the two-center interference regions. Therefore, the small (large) intensity ratio between the accurate perpendicular harmonic and accurate parallel harmonic can be attributed to the contributions of the excited state to harmonics. Then we can conclude that the harmonic spectra that only go back to the ground state show high (small) ellipticity, whereas the accurate harmonic spectra show small (high) ellipticity, resulting in a strong angle dependence of the influence of the excited state on the ellipticity of harmonic. In addition, in the high-order harmonic plateau region, the relative yields of harmonics can be well predicted by the corresponding dipoles, indicating the applicability of tunneling pictures and plane wave approximation in the strong and short-wave laser fields. When the ellipticity of harmonic occurs in the interference region due to the two-center characteristics of the symmetric potential, the results show that the polarization measurement can also be used to detect the structures of symmetric molecules and track the dynamic behaviors of excited states.

Optical Direction-Finding Based on Silicon Photonic Integrated Circuits

In this paper, a high accuracy direction-finding (DF) system based on silicon photonic integrated circuits (PIC) is proposed. The accurate direction of a target can be determined by its position in the reconstructed image obtained by spatial frequency (SF) sampling and inverse Fourier transform according to theories of interferometric imaging. With the help of numerical simulation, we designed a multi-baseline structure which could significantly improve the accuracy and angular range of DF system. To address the integration and stability problems which confine the application of DF techniques, we innovatively implemented our multi-baseline structure on Silicon-On-Insulator (SOI) platform. Thermal phase-shifters and multi-mode interferometers are employed for on-chip quadrature modulation detection. By testing the fabricated DF chip with a 1550nm laser source at 14 different positions, we verified its DF accuracy and stability. The experimental results show excellent DF performance with an average angular error ∼215.71 µrad and prove the potential of our technique in high precision DF applications.

Aiming to personalized laser therapy for nevus of Ota: melanin distribution dependent parameter optimization.

Aiming to the personalized laser therapy of nevus of Ota (NO), a local thermal non-equilibrium model was employed to optimize laser wavelength, pulse duration, and energy density under different melanin depth and volume fraction. According to our simulation, the optimal pulse duration is between 15 and 150ns to limit heat transfer inside the hyperplastic melanin, and 50ns is recommended to decrease the energy absorption by normal melanin in epidermis. Correlations of the minimum and the maximum energy densities are proposed with respect to melanin depth and volume fraction for the 755-nm and 1064-nm lasers. For the same NO type, the therapy window of the 755-nm laser is larger than that of 1064-nm. For NO with shallow depth or low volume fraction, the 755-nm laser is recommended to make the treatment more stable owing to its lager therapy window. For deeper depth or higher volume fraction, the 1064-nm laser is recommended to avoid thermal damage of epidermis. Through comparison with clinical data, the optimized laser parameters are proved practicable since high cure rate can be achieved when energy density falls into the range of predicted therapy window. With developing of non-invasive measurement technology of melanin content and distribution, personalized treatment of NO maybe possible in the near future.

Influence of the focusing characteristics of near-infrared lasers on the maintenance of plasma luminescence

The interaction of 980-nm continuous laser radiation with the plasma of a continuous optical discharge in xenon lamps at a pressure of p = 12 atm has been studied. The threshold power and characteristics of the laser required to sustain the xenon plasma became our focus. According to the theory of Gaussian beam propagation, the laser parameters after collimation and focusing are obtained by combining ZEMAX simulation and the actual measurement. The influence of the beam waist ω0, which determines the power density distribution at focus, and the Rayleigh range Z0, which determines the energy concentration range, on the threshold maintenance power is expounded. The results show that there is a threshold power density for the generation of plasma, whose value is about 1,500–2,000 W/mm2, and that the threshold maintenance power of the plasma shows an overall decreasing trend with decreasing ω0. When ω0 is reduced to a higher power density that can easily maintain the thermodynamic equilibrium process of the plasma, the mismatch between Z0 and the plasma size caused by the decrease in Z0 makes the threshold power tend to be stable and increasing.

The effect of different irrigation and disinfection methods on post-operative pain in mandibular molars: a randomised clinical trial

BackgroundTo examine post-operative pain (PP) after conventional irrigation and sonic activation methods, with and without laser disinfection in mandibular molars.MethodsEighty patients with symptomatic apical periodontitis were included in this randomized clinical study. There were four study groups. In group 1, conventional irrigation only was applied. In group 2, a sonic irrigation activation system (EDDY (VDW, Munich, Germany)), was applied. In groups 3 and 4, irradiation with a 980-nm diode laser was performed, following irrigation with the conventional method and sonic irrigation activation system, respectively. The patients were instructed to record their PP and analgesic intake using a numerical rating scale 8, 24, 48 h and 7 days post-procedure. A chi-square test, Fisher’s exact chi-square test and Fisher–Freeman–Halton exact test were used to assess qualitative data. Inter-group and intra-group parameters were assessed using the Kruskal–Wallis test and Wilcoxon’s test at a significance level of p < 0.05.ResultsThere was no statistically significant difference among the groups in terms of age, sex, pre-operative pain, PP and analgesic intake (p > 0.05).ConclusionsThe use of sonic irrigation activation system in the final irrigation protocol and irradiation with the 980-nm diode laser did not significantly reduce PP levels and analgesic intake.

Enhanced 3.1µm mid-infrared emission from Er3+/Yb3+ co-doped tellurite glass pumped by 980nm laser diode

Yb3+ ions co-doping was attempted for the first time for sensitizing Er3+ ions and increasing the 3.1 µm fluorescence, originating from the transition from Er3+: 4S3/2 → 4F9/2. Under a 980 nm LD excitation, strong 3.1 µm fluorescence in the mid-infrared (MIR) region and the related energy level change process were investigated. An enhanced 3.1 µm emission was attained from the Er3+/Yb3+ co-doped tellurite glass with the increment in Yb2O3 content, which demonstrated that the Yb3+ ions may act as the sensitizer to the Er3+ ions, thereby providing an effective energy transport channel from the 2F5/2 state of Yb3+ ions to the 4S3/2 state of Er3+ions. Moreover, the measured emission band full width at half maximum reaches about 164 nm along with the maximum emission cross-section (2.88 × 10−21 cm2). The outcome of our work suggests that upon co-doping with Er3+/Yb3+, the tellurite glass may function as a prospective material for fabricating the matrix of 3.1 µm MIR lasers.

Generation of Terahertz Radiation under the Femtosecond Laser Excitation of a Multilayer Structure Based on a-Si:H/a-SiC:H/c-Si

Coherent terahertz radiation has been generated in p–n heterostructures based on a-Si:H/a-SiC:H/c-Si excited by 800-nm femtosecond laser pulses at room temperature. Terahertz radiation is generated when a reverse bias voltage is applied to heterostructures. The properties of the generated terahertz radiation strongly depend on the bias voltage, which reflects the dynamics of nonequilibrium charge carriers produced by femtosecond laser pump in the heterostructure.

Design and electrospinning synthesis of SrF2:Er3+/Yb3+ unidimensional nanostructural materials with tunable upconverting fluorescence

In order to develop new morphology and properties of up-converting fluorescent materials, SrF2:Er3+/Yb3+ up-converting fluorescent unidimensional nanostructural materials including nanofibres, nanostrips and hollow nanofibres have been designed and successfully constructed via a uniaxial electrospinning associated with a bi-crucible fluorination technology. Controllable fabrication of unidimensional nanostructural materials is successfully realized via controlling the ingredients and proportions of the spinning solutions and spinning parameters. The influences of roasting temperature, molar proportion of Yb3+ to Er3+ and morphology on the up-converting fluorescence of the samples are studied in detail, and further tunable fluorescence is achieved. Upon the excitation of 980-nm laser, the unidimensional nanostructural materials display excellent up-converting fluorescence. The bright green emissions at 526 and 548 nm are assigned to the 2H11/2 → 4I15/2 and 4S3/2 → 4I15/2 energy levels transition of the Er3+ ions, respectively, and the weaker red characteristic emission peak at 652 nm is attributed to the 4F9/2 → 4I15/2 energy level transition of Er3+. Further, the detailed fluorescent mechanism and the formative mechanism of the unidimensional nanostructural materials are expounded in-depth, and the fabrication techniques are built. Much more importantly, the designing philosophy and fabricating technology can be popularized to manufacture other metal fluoride unidimensional nanostructural materials. The as-synthesized SrF2:Er3+/Yb3+ unidimensional nanostructural materials may find tremendous potential applications in the areas of emitting diodes, displaying devices, optical probes, bioimaging, sensing, drug delivery and lithium-sulfur batteries.

Ultrafast Imaging of Molecular Chirality with Photoelectron Vortices.

Ultrafast imaging of molecular chirality is a key step toward the dream of imaging and interpreting electronic dynamics in complex and biologically relevant molecules. Here, we propose a new ultrafast chiral phenomenon exploiting recent advances in electron optics allowing access to the orbital angular momentum of free electrons. We show that strong-field ionization of a chiral target with a few-cycle linearly polarized 800nm laser pulse yields photoelectron vortices, whose chirality reveals that of the target, and we discuss the mechanism underlying this phenomenon. Our Letter opens new perspectives in recollision-based chiral imaging.

Safety and Effectiveness of Diode Laser Used in Stapes Surgery.

Objective: We comprehensively assessed the safety and effectiveness of a 980-nm diode laser with fiberoptic delivery in stapes surgery by laser energy use, complications, and audiometric outcomes. Materials and methods: We retrospectively reviewed 116 primary stapes surgery cases. A high-power (30-40 W), short-pulse (60 msec), 980-nm diode laser was used for superstructure removal and footplate fenestration in the diode laser group (DLG) and, the hook and drill method in the conventional technique group (CTG). Data on complications and surgical diode laser use were collected; audiometric results within 6 months postoperatively were included in the analysis. Results: In DLG, the median fenestration and superstructure resection energy were 4.80 and 18.23 J, respectively. Footplate floating occurred in two ears (2/128, 1.56%) with manual fenestration, although none in the DLG (p = 0.07). Six CTG patients (6/26, 23.08%) underwent inevitable stapedectomy owing to footplate dislocation, which was higher than that in the DLG (2.11%, p < 0.01). No patients in the DLG experienced sensorineural hearing loss, and bone conduction (BC) improved at 1 (preoperative and postoperative means: 23.69 and 20.93 dB, respectively; p = 0.003) and 2 kHz (preoperative and postoperative means: 35.28 and 31.40 dB, respectively; p < 0.001), whereas changes in BC at 0.5 and 3 kHz were stable (p > 0.05). Four DLG patients (4/107, 3.74%) experienced transient facial nerve palsy postoperatively. Laser energy analysis showed shorter superstructure vaporization intervals in patients with transient facial nerve palsy (mean, 11.65 sec; median of control, 24.57 sec; p = 0.037). Conclusions: High-power, short-pulse, 980-nm diode laser is safe and effective in stapes surgery.

Laser diode-pumped compact hybrid lithium niobate microring laser.

We demonstrate a compact hybrid lithium niobate microring laser by butt coupling a commercial 980-nm pump laser diode chip with a high-quality Er3+-doped lithium niobate microring chip. Single-mode lasing emission at 1531-nm wavelength from the Er3+-doped lithium niobate microring can be observed with the integrated 980-nm laser pumping. The compact hybrid lithium niobate microring laser occupies the chip size of 3 mm × 4 mm × 0.5 mm. The threshold pumping laser power is 6 mW and the threshold current is 0.5 A (operating voltage 1.64 V) at atmospheric temperature. The spectrum featuring single-mode lasing with small linewidth of 0.05 nm is observed. This work explores a robust hybrid lithium niobate microring laser source which has potential applications in coherent optical communication and precision metrology.

Optical fiber temperature sensor based on the fluorescence intensity ratio of bismuth–erbium co-doped optical fiber

In our work, the temperature sensing properties and intrinsic mechanism based on a bismuth–erbium co-doped optical fiber (BEDF) were explored. Through temperature sensing experiments, we found that when the 980-nm pump laser was used, the fluorescence intensity ratio (FIR) at 1560 and 1435 nm showed a good linear relationship at different temperatures and its sensitivity reached 0.1151 dB/°C, the accuracy was 0.2°C, and the R2 of the FIR curve is about 0.9923. At the same time, we also proposed a detection algorithm to judge the working state of the sensor. By changing the BEDF coating material while the fiber is being fabricated, the temperature measurement range can be further improved. The optical fiber temperature sensor will have a broader range of applications.

Angular distribution of near-threshold photoelectrons from resonance-enhanced multiphoton ionization of argon

We experimentally study the angular distribution of near-threshold photoelectrons of argon in the multiphoton-ionization regime. Those near-threshold photoelectrons are released from atoms by a weak 800-nm laser field and a strong 400-nm laser field with parallel polarizations. In the laser polarization direction, the yield of the near-threshold photoelectron oscillates with twice the 800-nm laser frequency, while higher-frequency components for the yield oscillations are found for the electrons emitted perpendicular to the laser polarization direction. By decomposing the photoelectron angular distribution into different partial waves, we found that those near-threshold photoelectrons are generated by the interference of different photon channels via resonant states. Moreover, we observed a large time delay between the near-threshold photoelectrons emitted along the laser polarization direction via the $5p$ and $4f$ resonant states.

Magnetometry based on the effect of laser-induced plasmas in a sodium-containing environment.

The magneto-optical resonance response of sodium atoms generated by a high-energy solid-state pulse Nd:YAG laser is studied in different external magnetic fields. We investigate the resonance fluorescence signal of sodium atoms in a simulated sea fog environment based on the laser-induced plasma (LIP) effect. By ionizing an NaCl solution spray to generate sodium atoms in an atmospheric environment, we build a Bell-Bloom magneto-optical resonance system under laboratory conditions. With the help of laser-induced breakdown spectroscopy (LIBS) and extinction spectrum, we obtain sodium atoms with a lifetime of 250 µs. A narrowband tunable continuous wave (CW) 589-nm laser tuned at the D2 line with a modulation frequency around the Larmor frequency is used as the pump beam to polarize sodium atoms in the test magnetic field. We find that the magneto-optical resonance signals vary with different external magnetic fields and the positions of the resonance signal are consistent with the theoretical values. An intrinsic magnetometric sensitivity of 620.4 pT in a 1-Hz bandwidth is achieved.

Experimental investigation on a hundred-Watt monolithic fiber laser operating near 980 nm with 20/125-μm double-cladding Yb-doped fiber

• A hundred-Watt 980-nm MOPA fiber laser is demonstrated with the 20/125-μm DCYF. • In-band ASE limits the power up-scaling of the MOPA fiber laser. • Increasing seed power is beneficial to suppress the in-band ASE. • Split-step seed loading method is presented, with which 109-W output power is achieved. • The fiber laser provides a cost-effective solution for high-power core-pumping source. In this paper, a hundred-watt monolithic fiber laser operating near 980 nm is demonstrated by using a double-cladding Yb-doped fiber (DCYF) with 20-μm core and 125-μm inner-cladding diameter. The fiber laser is fabricated with the master oscillator power amplifier (MOPA) configuration to scale up the output power. In our experiment, it is found that the power scalability of the fiber laser is limited by the in-band amplified spontaneous emission (ASE) which can be effectively suppressed by increasing the seed power. Then, with the split-step seed loading method, 109-W output power around 980 nm has been achieved with in-band and 1030-nm ASE suppressed to 17.1 and 40.6 dB, respectively. The beam quality has also been measured, and the M 2 factor is about 1.9 at the maximum output power. Our work provides a cost-effective solution to achieve hundred-Watt fiber lasers operating near 980 nm.

Effectiveness of collagen cross-linking induced by two-photon absorption properties of a femtosecond laser in ex vivo human corneal stroma.

This study aimed to investigate the effectiveness of two-photon induced collagen cross-linking (CXL) using femtosecond lasers in human corneal stroma. An 800-nm femtosecond laser optical path for CXL was established. Corneal samples that received two-photon induced CXL and ultraviolet-A (UVA) CXL underwent uniaxial stretching experiments, proteolytic resistance assays and observation of collagen fiber structure changes. Two-photon induced CXL can achieve corneal stiffening effects comparable to UVA CXL and showed better advantages at low strains. The cornea after two-photon induced CXL exhibited high enzymatic resistance and tight collagen fiber arrangement. Two-photon induced CXL promises to be a new option for keratoconus.

The excellent dual optical thermometry of the Yb3+, Er3+ doped SrLu2O4

SrLu2O4: Yb3+, Er3+ samples were achieved successfully via a traditional solid-state method at 1450 °C. As 980-nm laser exciting, the UC spectra include red and green emissions mainly centering on 665 and 552 nm, respectively. The red is dominant, and the green part is a relative weakness. For all co-doped samples, intense red radiation is obtained. Meanwhile, the experimental formulas about pumping power and spectrum intensity helped us comprehend the up-conversion processes further, and the conclusion is a two-photon process in UC. The 4S3/2 and 2H11/2 levels ions are thermal coupled energy levels. We also investigated thermometric characteristics of the samples on the fluorescence intensity ration technology. For SrLu2O4: Er3+/Yb3+, it can be used as a temperature sensor by using its green emission and red emission, and the sensor sensitivity was calculated. The maximum absolute sensitivity and the relative sensitivity is 0.00226 K-1 and 0.0119 K−1 at 513 K for green emission and the maximum absolute sensitivity and the relative sensitivity is 0.00126 K-1 and 0.0026 K−1 at 303 K for red emission. The fluorescence intensity ratio (FIR) values are almost stable and accurate in repeated tests. As a result, the SrLu2O4: Er3+/Yb3+ samples would useful hopefully to optical engineering and sensors.

Spectral beam combining of diode lasers extended into the non-SBC direction.

An extended spectral beam combining (SBC) configuration that folds the optical path of the combining laser into the non-SBC direction and doubly narrows the SBC spectrum by introducing a right angular prism is proposed. Similar combined power and beam quality but half of the spectral width and a smaller size are demonstrated by comparing the standard SBC with the proposed SBC of the same 800nm laser bar. It provides an effective way to miniaturize the SBC size, improve the SBC stability and compress the SBC spectrum simultaneously. As far as we know, this study is also the first to report on folding the SBC optical path to the non-SBC direction, which provides a new idea for the SBC source.