Laser Output Power Research Articles

Antiresonant fiber-enhanced Raman spectroscopy gas sensing with 1 ppm sensitivity.

Antiresonant hollow-core fiber (AR-HCF) exhibits unprecedented optical performance in low transmission attenuation, broad transmission bandwidth, and single spatial mode quality. However, due to its lower numerical aperture, when utilizing the Fiber-Enhanced Raman Spectroscopy (FERS) principle for gas detection, the efficiency of AR-HCF in collecting Raman signals per unit length is significantly lower than that of hollow-core photonic crystal fiber. Nonetheless, AR-HCF effectively suppresses higher-order modes and offers bandwidth in hundreds of nanometers. By increasing the length of AR-HCF, its advantages can be effectively harnessed, leading to a considerable enhancement in the system's ability for low-concentration gas detection. We combine the nodeless antiresonant hollow-core fiber and Raman spectroscopy for enhanced Raman gas sensing in a forward scattering measurement configuration to investigate the attenuation behavior of the silica background signals. The silica background attenuation behavior enables the low baseline of the gas Raman spectroscopy and extends the integration time of the system. In addition, a convenient spatial filtering method is investigated. A multimode fiber with a suitable core diameter was employed to transmit the signal so that the fiber end face plays the role of pinhole, thus filtering the silica signal and reducing the baseline. The natural isotopes 12C16O2, 13C16O2, and 12C18O16O in ambient air can be observed using a 5-meter-long AR-HCF at 1 bar with a laser output power of 1.8 W and an integration time of 300 seconds. Limits of detection have been determined to be 0.5 ppm for 13C16O2 and 1.2 ppm for 12C16O2, which shows that the FERS with AR-HCF has remarkable potential for isotopes and multigas sensing.

Study on the mechanism of fiber-optic hot-wire sensing based on DFB-FL thermally induced chirp effect

In this paper, we propose an intensity demodulated fiber-optic hot-wire sensing method based on the thermally induced chirp effect of distributed feedback fiber lasers. The cobalt-doped fiber is fused at the rear end of the erbium-doped distributed feedback fiber laser to constitute a hot fiber wire with a gradient temperature distribution. The cobalt-doped fiber is heated up under the excitation of the residual pump light. Then the thermally chirp of the erbium-doped phase-shifted fiber grating brings out the change of the lasing threshold condition of the distributed feedback cavity and a significant reduction of the output power. When this structure is further altered by thermal induced chirp under external thermal field, the lasing output power will be further changed. The experimental results of the dynamic fluid thermal field and the static thermal field shows that, the fiber-optic hot-wire structure can sensitively detect the weak airflow and the thermal field of the environment by monitoring the laser power.

Diode-pumped Tm:YAP laser operating at 2.3 µm with enhanced performance through cascade lasing.

The laser diode (LD)-pumped Tm:YAP (a-cut, 3.5 at.%) laser generated a maximum ∼2.3 µm continuous wave (CW) laser output power of ∼3 W. The higher output power benefited from the positive effect of the cascade lasing (simultaneously operating on the 3H4 → 3H5 and 3F4 → 3H6 Tm3+ transition). It was the highest CW laser output power amongst the LD/Ti:Sapphire-CW-pumped ∼2.3 µm Tm3+-doped lasers reported so far. Under the cascade laser operation, the slope efficiency of the ∼2.3 µm laser emission versus the absorbed pump power increased from 13.0% to 21.4%.

Dual-ended pumped high-power 915 nm Pr3+:LiYF4 laser and power scaling under energy levels cascade

We reported a high-power 915 nm Pr3+:LiYF4 (Pr:YLF) laser dual-ended pumped by laser diodes (LDs). The maximum output power of the laser was 3.39 W with a slope efficiency of 19.8 %. The fluctuation range of the laser wavelength was less than 0.58 nm. As far as we know, this is the highest power at 915 nm for LD-pumped Pr:YLF lasers to date. To eliminate the power saturation phenomenon and further improve the laser output power, we proposed a simple and effective method, i.e., laser energy levels cascade. Based on the experimental data, we calculated the populations of 3P0 and 1G4 energy levels in Pr:YLF crystal during laser cascading and developed two different models to verify the feasibility of the laser cascade mechanism. Moreover, the laser cascade could be realized merely by designing the lens film without introducing other devices, which provided a simple and effective solution for developing high-performance lasers.

Microstructure – Properties relationship in laser-welded AZ31B magnesium alloy

The AZ31B magnesium alloy was laser-welded at three different (1.2, 1.6, and 2 kW) laser output powers in the present work. All the butt weld joints are almost defect-free. The size of the weld joint slightly increases with increasing laser output power. The weld metal is formed by columnar grains of the alpha phase at the weld metal/base metal interface, but a finely equiaxed grain microstructure is formed in the centres of fusion zones. The minor phases are Mg17Al12 and (Al,Mg)8Mn5. The weld metal microstructure manifests clear refinement with a decrease in laser output power. Microstructural changes are reflected in changes in mechanical properties; weld joints prepared at the lowest laser output power manifest the highest microhardness, ultimate tensile strength, yield strength, and almost 90% joint efficiency. This is related to the different extents of strengthening mechanisms that act most effectively in weld joints made at 1.2 kW laser output power. Detail analysis of fracture surfaces confirmed that lower laser output power and general microstructural refinement favours the formation of plastically deformed material, which is in excellent agreement with both the experimentally determined and the calculated values of yield strength.

High repetition frequency tunability active Q-switched all-fiber laser by multi-gain sub-rings smoothing multipeak pulse and suppressing ASE self-saturation.

This paper provides a method to effectively suppress the severe ASE self-saturation when achieving high repetition frequency tunability with high output power and narrow pulse width in active Q-switched all-fiber lasers. By studying the regularity of the system's multi-stable state, we first ensured that the laser system operated in a steady state. Then output avoids uneven distribution of pulse energy or missing pulses due to period bifurcation state or chaos state. By adding multiple gain sub-rings within the cavity, the sub-ring structure itself indirectly mitigates the ASE self-saturation while smoothing the pulse. The method will avoid the severe power loss caused by traditional smoothing methods by adjusting the AOM rising edge time. It will also avoid lowering the ASE lasing threshold at high repetition frequency. Meanwhile, the intra-cavity backward ASE can be effectively absorbed by inserting the gain fiber in the sub-rings to directly mitigate the ASE self-saturation. The system's continuously adjustable repetition frequency can be as high as over 300 kHz. It ensures that output power above the watt level and a < 0.2 nm narrow bandwidth can be maintained while tuning the repetition frequency. The narrowest smoothing pulse width of 28 ns has been reached.

Research on self phase-locked two-channel narrow linewidth laser

We have designed and constructed a self phase-locked two-channel narrow linewidth solid-state laser based on reflective volume Bragg grating (RVBG) as the output mirror. The resonant cavity of the laser is designed as a U-shaped structure, and two independent laser diode (LD)-side-pumped modules achieve passive phase locking of the output laser through mutual injection of photon energy. Compression of the linewidth is achieved by the RVBG. When the LD pump power was 70 W, the output powers of the two-channel lasers were 1.59 W and 1.61 W, the measured central wavelengths of the spectra were 1064.23 nm and 1064.24 nm, and the linewidths were 0.10 nm and 0.11 nm, respectively. The slope efficiencies of the two lasers are 9.5 % and 9.56 %, respectively, and their powers stability were both better than 3 %. The beam quality factors were Mx2=1.29, My2=1.31 and Mx2=1.32, My2=1.36, respectively. The interference fringes formed by the coherent superposition of two laser beams in the far field were observed through CCD, which verified the phase-locked coherence characteristics of the two lasers. The output power of the coherent combination laser is 2.64 W, with a corresponding efficiency of coherent combination is 82.5 %. The experimental results show that the laser can directly obtain two-channel narrow-linewidth continuous wave lasers output with phase locking and consistent laser intensity. Our research provides a new idea for obtaining a new type of high-quality narrow-linewidth coherent laser source

Anti-scattering signal processing method of VMD-ICA based underwater lidar

This paper proposes an underwater signal processing method based on the combination of variational mode decomposition (VMD) and independent component analysis (ICA). In this method, the VMD is used to decompose a set of echo signals into groups of eigenmodal signals arranged according to the order of their frequencies. These modal signals are then used as an observation matrix for ICA to ensure the integrity of the separated target echo signals. In this method, the correlation between the decomposed modal signals and the original signal is used to select the signals which are used as input matrix rows for ICA. The signal-to-clutter ratio is used to determine the number of decomposed layers. The ICA is used to separate the scattering and target echoes, so as to recover the weak target echoes in the strongly scattered water and greatly improve the ranging accuracy. A 532 nm intensity-modulated continuous wave (CW) laser is used in the underwater ranging experiments. The attenuation coefficient of the water is changed by adding Mg(OH)&lt;sub&gt;2&lt;/sub&gt;, ranging experiments are carried out at different attenuation lengths. The experimental results show that the signal processing method can be used to successfully measure the target within 9 AL (attenuation length) when the laser output power is 2.3 W, and the ranging accuracy is improved from 16 cm to less than 5 cm by using the algorithm. The proposed method can be applied to underwater lidar application in turbid water and long distance ranging underwater where the scattering dominates the echoes.

509 nm high power wide-tuned external cavity surface emitting laser

High power widely tunable green lasers have potential applications in many fields such as biomedical, lidar, laser spectroscopy, laser display, underwater wireless optical communication, fine processing of nonferrous metals, and so on. Vertical-external-cavity surface-emitting lasers, also known as semiconductor disk lasers, have the advantages of high power, good beam quality and wide bandwidth of gain medium. In this paper, a gain chip with reverse-growth epitaxy structure and emitting wavelength of 1018 nm is designed. A bandwidth of 74 nm above the reflectivity of greater than 99.1 % in the DBR reflection spectrum is obtained, which lays a solid foundation for the realization of high-power widely tunable output. The laser cavity combines a 1018 nm semiconductor gain chip, a folded mirror, and a plane mirror to construct a compact V-shaped resonant cavity. A class I phase-matched LBO nonlinear crystal with a length of 10 mm is placed at the beam waist of the cavity to realize a highly efficient frequency doubling process to produce 509 nm green laser. To meet the requirement of the polarization during frequency conversion and to tune the oscillating wavelength of the laser, a birefringent filter (BRF) is employed in the laser resonant cavity. When the thickness of the used BRF is 1 mm, the obtained wavelength tuning ranges of the fundamental laser and the frequency doubled green laser are 47.1 nm and 20.1 nm, respectively, showing a good tuning capability of the laser. The laser's performance varies with the different thickness of the BRF. When using a 2 mm BRF, a maximum output power of the frequency-doubled green laser of 8.23 W is achieved during continuous tuning, indicating an ideal compatibility of wide tuning characteristics and a high output power. Meanwhile, its beam quality M&lt;sup&gt;2&lt;/sup&gt; factors are 1.00 and 1.03 in the x and y directions, respectively, demonstrating a near diffraction-limited excellent beam quality. This green laser also possesses a frequency doubling conversion efficiency of up to 68.2 %, which enables efficient conversion of the fundamental laser into the frequency doubled green laser. The optical-to-optical conversion efficiency from the absorbed pump light to the frequency-doubled green light also reaches 16.6 %. Meanwhile, the spectral linewidths of the green lasers under different thicknesses of BRFs are found that the thicker the BRF, the narrower the laser line widths, which is consistent with the theoretical results.

Intracavity frequency-doubled external-cavity surface-emitting blue laser with high conversion efficiency

Blue laser with high power and high beam quality has many applications such as in laser display, underwater communication and imaging, and non-ferrous metal processing. Optically pumped external-cavity surface-emitting laser combines the advantages of both surface-emitting semiconductor lasers and solid-state disk lasers, and can produce high output power and good beam quality simultaneously. Its high intracavity circulating power is more conducive to intracavity frequency doubling, achieving high-power and high beam quality blue light through fundamental laser in the near-infrared waveband. This paper reports an efficient intracavity frequency doubled 490 nm high power blue light by using a 980 nm fundamental laser in an external-cavity surface-emitting laser. The V-type resonant cavity is formed by the high reflectivity distributed Bragg reflector (DBR) at the bottom of gain chip, a folded flat concave mirror (high reflectivity coated for 980 nm and anti-reflectivity coated for 490 nm), and a flat concave end mirror (high reflectivity coated for 980 nm and 490 nm). By inserting a nonlinear crystal LBO into the cavity at the beam waist formed by the folded mirror and end mirror, and employing a birefringent filter (BRF) to polarize the fundamental laser and narrow the linewidth of the laser, a high power and high beam quality blue laser with high conversion efficiency is obtained. The effects of different factors including the length of nonlinear crystal, the linewidth of fundamental laser, and the compensation of walk off angle on the output power of the blue laser are studied experimentally. The length of the nonlinear crystal is optimized based on the size of the fundamental laser beam waist at the position of the crystal in the resonant cavity. Under the type-I phase matching condition of LBO, over 6 W output power at 491 nm wavelength is obtained when the crystal length is 5 mm and the BRF thickness is 1 mm. The beam quality &lt;i&gt;M&lt;/i&gt;&lt;sup&gt;2&lt;/sup&gt; factor in the &lt;i&gt;x&lt;/i&gt; direction and the &lt;i&gt;y&lt;/i&gt; direction are both 1.08, and the conversion efficiency of frequency doubling is 63%. The experimental results also show that symmetrically placed nonlinear crystals can compensate for the walk-off angle during frequency doubling to a certain extent, thereby clearly improving the conversion efficiency of the frequency doubled blue laser.

Watt-level LED-pumped actively Q-switched 1319 nm laser with high repetition rate operation

In this paper, we exhibited a watt-level acousto-optical (A-O) Q-switched 1319 nm laser based on a high-efficiency LED-pumped Nd:YAG laser module with high average power and high repetition rate operation. For the quasi-continuous wave (QCW) running operation, the average output power of fundamental laser at 1319 nm was as high as 4.73 W with a pulse length of 972 μs at a repetition rate of 100 Hz. After the resonator structure was optimized by A-O Q-switched modulation, the maximum power was 2.35 W at a repetition frequency of 5 kHz with a pulse width of 1.52 μs, and the M2 factor was measured to be about 9.4. To the best of my knowledge, this is the first demonstration, the maximum average power and high repetition rate watt-level output of an LED-pumped A-O Q-switched 1319 nm laser reported to date.

Experimental evaluation of a WC–Co alloy layer formation process by multibeam-type laser metal deposition with blue diode lasers

A tungsten carbide–cobalt (WC–Co) composite layer was formed on a stainless-steel type 304 (SS304) substrate using multibeam laser metal deposition (LMD) with blue diode lasers. This paper aims to provide WC–Co layer formation with low porosity and high layer formation efficiency by using the multibeam LMD process. The effects of process parameters such as laser output power and powder feed rate are tied together to explain the geometry of the melt layer as well as the fraction of the laser energy used for melting a material. The experimental results show that the porosity rate and layer formation efficiency were recorded at 0.3% and 0.0042 mm3/J, respectively, at the laser output power of 180 W and a powder feed rate of 75 mg/s. It was revealed that layer formation efficiency was dependent on the laser output power.

Comparison of the Diode Laser Wavelengths 445 nm and 810 nm in Gingival Depigmentation - A Clinical Evaluation.

Introduction: Nowadays, esthetic appearance plays an important role in the field of dentistry. Discolorations and pigmentations of the gingiva reduce the appearance of a healthy-looking smile. On this occasion, the use of lasers shows a promising approach for a fast and non-aggressive treatment in this field. Different laser wavelengths are being used for gingival depigmentation this clinical study aimed to investigate the effect of the novel laser wavelength (445 nm) in this field and compare it with an 810 nm diode laser. Methods: Two diode laser wavelengths (445 nm and 810 nm) were used for depigmentation. The laser output power chosen was 1 W. An optical fiber with a diameter of 400 µm was used. 21 patients with pigmented gingiva were selected. Depigmentation was carried out in a split-mouth design for a direct comparison of the clinical effect. Outcomes were documented by photograph after one month and six months of follow-up. Results: For each wavelength, 21 volunteers evaluated 21 clinical cases of depigmentation, which means that 441 comparisons were carried out in total regarding the color change from brownish to pinkish. A 100% clarification was achieved for 445 nm. In the 810 nm group, the color change in 44 of 441 cases (10%) could not be clearly identified. No statistically significant difference in pain experience was reported for both laser treatments. Conclusion: The clinical evaluation showed that within the limitations of this study, most of the clinical outcome parameters were highly acceptable by the patients due to mild pain and discomfort for both laser systems.

Study on Surface Roughness, Morphology, and Wettability of Laser-Modified Powder Metallurgy-Processed Ti-Graphite Composite Intended for Dental Application.

In this study, the surface laser treatment of a new type of dental biomaterial, a Ti-graphite composite, prepared by low-temperature powder metallurgy, was investigated. Different levels of output laser power and the scanning speed of the fiber nanosecond laser with a wavelength of 1064 nm and argon as a shielding gas were used in this experiment. The surface integrity of the machined surfaces was evaluated to identify the potential for the dental implant's early osseointegration process, including surface roughness parameter documentation by contact and non-contact methods, surface morphology assessment by scanning electron microscopy, and surface wettability estimation using the sessile drop technique. The obtained results showed that the surface roughness parameters attributed to high osseointegration relevance (Rsk, Rku, and Rsm) were not significantly influenced by laser power, and on the other hand, the scanning speed seems to have the most prevalent effect on surface roughness when exhibiting statistical differences in all evaluated profile roughness parameters except Rvk. The obtained laser-modified surfaces were hydrophilic, with a contact angle in the range of 62.3° to 83.2°.

Evaluation of laser power stability of repeatedly used SubCyclo probe in micropulse transscleral cyclophotocoagulation for glaucoma: A step towards sustainable ophthalmic surgery

Purpose To evaluate the laser power stability of the SubCyclo probe for micropulse transscleral cyclophotocoagulation after repeated use. Materials and methods This experimental study involved 6 new probes. Each probe was connected to the SubCyclo mode (2,000 mW power, 31.3% duty cycle, and 100 seconds duration) of the Vitra 810 laser delivery system (Quantel Medical, France). Laser power measurements were taken using a calibrated laser power meter (Nova, Ophir Optronics Solutions, Israel) every 10 seconds from 10 to 90 seconds during each of the 40 cycles. Intra-rater reliability was assessed using intraclass correlation (ICC). A linear mixed model for repeated measures and pairwise comparisons with Bonferroni adjustment were used for the analysis. Results The mean (SD) power outputs of all probes for the first cycle and all cycles were 421.9 (19.7) mW and 436.7 (16.1) mW, respectively. During the first cycle, the mean (SD) laser power gradually decreased from 444.3 (13.4) mW at 10 seconds to 407.3 (17.0) mW at 90 seconds (Fig 3). For all cycles, the power was 446.0 (13.6) mW at 10 seconds and gradually declined to 426.8 (21.0) mW at 90 seconds. Pairwise comparisons revealed significant differences in mean laser power outputs after 16 cycles of repeated use compared to the first cycle. The ICC estimate (95% CI) for intra-rater reliability was 0.96 (0.89, 0.99). Conclusions The SubCyclo probe maintains stable laser power outputs throughout repeated use for up to 16 cycles, with a significant increase observed after 16 cycles.

Efficient continuous-wave Nd:YVO4/KGW intracavity Raman laser

We demonstrate an efficient Nd:YVO4/KGW intracavity Raman laser in continuous-wave (CW) scheme. With a V-shaped fundamental laser cavity and a short Stokes cavity in it, the oscillating beam sizes are designed to alleviate the thermal effect and to enhance the Raman gain for efficient CW operation. The output power of CW Stokes wave at 1177 nm reached 9.33 W under an incident laser diode pump power of 36.65 W, with corresponding optical efficiency being 25.5%. To the best of our knowledge, these are the highest Stokes output power and conversion efficiency of CW intracavity Raman lasers.

Random Raman Fiber Laser as a Liquid Refractive Index Sensor

In this paper, a new concept of forward-pumped random Raman fiber laser (RRFL)-based liquid refractive index sensing is proposed for the first time. For liquid refractive index sensing, the flat fiber end immersed in the liquid can act as the point reflector for generating random fiber lasing and also as the sensing head. Due to the high sensitivity of the output power of the RRFL to the reflectivity provided by the point reflector in the ultralow reflectivity regime, the proposed RRFL is capable of achieving liquid refractive index sensing by measuring the random lasing output power. We theoretically investigate the effects of the operating pump power and fiber length on the refractive index sensitivity for the proposed RRFL. As a proof-of-concept demonstration, we experimentally realize high-sensitivity half-open short-cavity RRFL-based liquid refractive index sensing with the maximum sensitivity and the sensing resolution of–39.88W/RIU and 2.5075×10−5 RIU, respectively. We also experimentally verify that the refractive index sensitivity can be enhanced with the shorter fiber length of the RRFL. This work extends the application of the random fiber laser as a new platform for highly-sensitive refractive index sensing in chemical, biomedical, and environmental monitoring applications, etc.

Efficient dual-end pumped a-cut Er:Yb:YAl3(BO3)4 microchip laser

This paper presents the findings of a high-efficiency continuous-wave (CW) microchip laser operating at 1.5 μm, utilizing an a-cut Er:Yb:YAl3(BO3)4 (Er:Yb:YAB) crystal. The laser was effectively pumped using a dual-end co-polarization configuration. The temperature distribution within the Er:Yb:YAB crystal, as simulated through finite element analysis, substantiates the efficacy of the dual-end pumping approach in enhancing the thermal gradient within the crystal. A CW Er:Yb:YAB microchip laser with the maximum polarized output power of 2.79 W was obtained with the pump power of 16.2 W at the wavelength of 1531 nm. To the best of our knowledge, this is the largest CW polarized laser output power in the reported Er:Yb:YAB microchip laser. The beam quality factors of our output laser are M2x = 1.54 and M2y = 1.57, which shows better beam quality than single-end pumped Er:Yb:YAB microchip laser.

Blue LD-pumped continuous wave a-cut Pr3+:LiYF4 near-infrared laser at 868 nm

We reported an 868 nm Pr3+:LiYF4 (Pr:YLF) laser pumped by an InGaN blue laser diode (LD) for the first time. The maximum power of the laser was 641 mW and the beam quality Mx2 and My2 factors were ∼2.66 in the x-direction and ∼2.32 in the y-direction, respectively. The output power fluctuation was stable within ±2 %. The 868 nm laser was successfully realized in Pr:YLF crystal by designing and optimizing the laser resonant cavity and optical thin films. In addition, we theoretically simulated the nonlinear relationship between the laser output power and the absorbed pump power, and the theoretical simulation results were in agreement with the experimental data. The first realization of the 868 nm Pr:YLF laser further expands the near-infrared lasers.

Ultrafast Fiber Laser Based on Tungsten Sulphoselenide Materials

Tungsten sulphoselenide (WSSe) alloys, belonging to the transition metal dichalcogenide family, have attracted significant interest in the area of optoelectronics because of their unique optical and electronic properties. However, there has been a dearth of sufficient research on the saturable absorption features and ultrafast lasers applications. Herein, we fabricated a WSSe-microfiber saturable absorber (SA) based on WSSe nanosheets prepared by liquid exfoliation technique. The SA provided a saturation intensity of a modulation depth of 27.95% and a nonsaturable loss of 21.34%. To investigate the potential applications of WSSe in ultrafast photonics, the prepared WSSe-microfiber was incorporated into an Er-doped fiber laser ring cavity. The results demonstrated that the WSSe-based SA successfully generated mode-locking laser pulses with a remarkably short pulse width of 231 fs. Furthermore, the output power of this ultrafast fiber laser reached an impressive value of 15.68 mW. These findings provide valuable views into the unique features of WSSe alloys in the areas of ultrafast optics and develop recipes for SA in ultrafast fiber lasers.