Lanthanide-doped nanocrystals in high-Q microtoroids for stable on-chip white-light lasers
Limin Jin, Zhuo Liu, Yuqi Zhang, Yunkai Wu, Yilin Liu, Huachun Deng, Qinghai Song, and Shumin Xiao
The plentiful energy states of lanthanide (Ln3+)-doped nanomaterials make them very promising for on-chip integrated white-light lasers. Despite the rapid progresses, the Ln3+-based white upconversion emissions are strongly restricted by their low upconversion quantum efficiency and the color stability. Herein, we combine the CaF2:Yb35Tm1.5Er0.5 nanocrystals and the high-Q microtoroids, and experimentally demonstrate the chip-integrated stable white-light laser. By optimizing the sizes, density, and distributions of Ln3+-doped nanocrystals, the Q factors of Ln3+-doped microtoroids are maintained as high as 5×105. The strong light matter interaction in high-Q microtoroids greatly enhances the upconversion emission and dramatically reduces the laser thresholds at 652 nm, 545 nm, and 475 nm to similarly low values (1.89–2.10 mJ cm-2). Consequently, robust white-light microlaser has been experimentally achieved from a single microtoroid. This research has paved a solid step toward the chip-scale integrated broadband microlasers.
  • Jun. 13, 2022
  • Photonics Research
  • Vol. 10 Issue 7 07001594 (2022)
  • DOI:10.1364/PRJ.456381
Microstructure and Machinability of Laser Cladding Co-WC on High Speed Steel Tools for Numerical Control Machine Tools
Hu Guiling, Shi Peng, and Zhang Lei
  • Jun. 10, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 11 1114008 (2022)
  • DOI:10.3788/LOP202259.1114008
Establishment and Verification of Thermo-Mechanical Coupled Model for Laser Direct Deposition of Titanium Alloy
Li Bohong, Guo Shaoqing, Zhou Biao, Qin Renyao, Wang Tianyuan, and Zhao Zijun
The MSC Marc software is used to establish the thermal-mechanical coupled finite element model to analyze the evolution of temperature and stress deformation during laser direct deposition. Considering the stress relaxation behavior of titanium alloy at high temperature, the material constitutive equation is modified through several iterations. At the same time, based on the thermocouple and laser displacement sensor, a transient real-time measurement device is developed to measure the temperature and deformation of titanium alloy thin-wall parts during the actual forming process. By comparing and analyzing the simulated and measured values of the modified model, the results show that the temperature error between the in-situ measurement results and the simulated results is only 7.9%, the deformation error is 19.6%, and the laws of the substrate deformation are consistent. The stress in the deposition layer is generally tensile, and the main stress direction is consistent with the deposition direction.
  • Jun. 10, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 11 1114007 (2022)
  • DOI:10.3788/LOP202259.1114007
Quantitative Analysis of Mg Element in Aluminium Alloy Based on Laser-Induced Breakdown Spectroscopy
Ding Yu, Yang Linyu, Chen Jing, Wang Xingyu, Guo Xiaoran, Xu Xuanchen, Zhao Xingqiang, Luo Yong, and Chen Wenjie
Mg element can make the aluminum alloy to obtain better mechanical properties and form a corrosion-resistant spinel film on the surface of the alloy, so that the alloy has better corrosion resistance. Therefore, exploring a method that can quickly and accurately detect the content of magnesium in aluminum alloy quantitatively is of great significance. In this paper, first, the Mg element in 17 aluminum alloy samples is detected and analyzed based on laser-induced breakdown spectroscopy (LIBS) technology. Then, Nd:YAG laser is used as light source, and the partial least squares (PLS) and random forest (RF) models are respectively established, and the prediction performance of the models is analyzed. The experimental results show that for the same test set, the correlation coefficient (Rp2) of the PLS model is 0.6809, and the root mean square error (RMSE) is 1.2042; the Rp2of the RF model is 0.8571 and the RMSEis 1.0918. In order to improve the prediction accuracy of the random forest model, this experiment screened the input variables according to the importance of the variables. When the wavelength point with variable importance greater than 0.11 is selected, Rp2 of the RF model based on variable importance is 0.9461, and the RMSE is 0.9534. Compared with the prediction result of the RF model, Rp2 is increased by 10.38%, RMSEis reduced by 12.68%, and the modeling time is reduced by 91.67%.
  • Jun. 09, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 13 1314006 (2022)
  • DOI:10.3788/LOP202259.1314006
Parameter Optimization and Performance Test of Laser Cutting of Carbon Fiber Reinforced Plastics Based on Response Surface Method
Hou Hongling, Hao Hailing, Ruihu Lü, Zhao Yongqiang, and Wang Changqian
To improve the laser cutting quality of carbon fiber reinforced plastics, the response surface method was used to establish a mathematical model of each response index with slit entrance width, heat-affected zone width, and kerf taper angleas the response indexes. Thereafter, the influence law of the interaction of each laser parameter on the response indexes was analyzed, and the parameter optimization combination was obtained to minimize each response index using 755 W laser power, 20 mm/s cutting speed, -0.6 mm focus position, and 0.7 MPa air pressure. The predicted values of the response indexes were obtained. Next, the laser cutting test was conducted under the parameter optimization combination, and the differences between the response indexes slit entrance width, heat-affected zone width, and kerf taper angle and predicted values were 12.73 μm, 6.55 μm, and 0.12°, which were within the fluctuation range of the predicted values, proving the effectiveness of the parameter optimization combination. The laser-cut specimens with the parameter optimization combination increased the glued tensile shear strength by 22.86% compared with the specimens before the optimization. The parameter optimization combination improves the laser cutting quality and reduces the impact of laser cutting on the mechanical properties of the material.
  • Jun. 09, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 13 1314005 (2022)
  • DOI:10.3788/LOP202259.1314005
Numerical Investigation on Self-Similar Mode-Locked Er-Doped Fluoride Fiber Laser at 2.8 μm
Zeng Guangmin, Peng Jie, and Tang Pinghua
In this paper, the generation and propagation of self-similar pulses in an Er-doped mode-locked fiber laser based on saturable absorber (SA) are numerically investigated. Research results indicate that by using a germanium rod to compensate the cavity dispersion, the intracavity pulse of an erbium-doped fluoride fiber laser based on SA mode-locking can support self-similar pulses evolution when the net dispersion of the cavity is in the range of 0.020-0.048 ps2. Keeping the net dispersion of the cavity with 0.03 ps2, ideal parabolic pulse with a pulse width of 19.7 ps, a peak power of 630 W, and a pulse energy of 12.4 nJ is obtained. To further optimize the output properties of the laser, the effects of small signal gain and gain saturated energy of the gain fiber, as well as the modulation depth and saturated power of the SA on the pulse output properties are studied in detail, which provides reference for the design of self-similar mode-locked Er-doped fluoride fiber lasers.
  • Jun. 09, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 13 1314004 (2022)
  • DOI:10.3788/LOP202259.1314004
Q-Switched Mode-Locked Rectangular Noise-Like Pulse in L-Band Fiber Laser
Pan Jieyu, Geng Xu, Sun Mengqiu, and Wang Xude
The evolution characteristics of Q-switched mode-locked rectangular noise-like pulses were studied in an L-band erbium-doped fiber laser. By varying the pump power and polarization state, continuous-wave and Q-switched mode-locked based on rectangular noise-like pulses with 1600 nm central wavelength were realized in the fiber laser. The fundamental repetition rate and the maximum pulse width of the rectangular noise-like pulse were 1.64 MHz and 17.51 ns, respectively, and the repetition rate of the Q-switched mode-locked rectangular noise-like pulse could be tuned in the range of 8.14-18.18 kHz. The evolution trend of the Q-switched envelope width was opposite to that of the rectangular pulse width. The maximum average energy of the Q-switched envelope and the rectangular pulse inside the Q-switched envelope reached 1115.5 nJ and 24.89 nJ, respectively. The average peak power of the rectangular pulse was maintained at approximately 1 W. These results may aid in understanding the dynamic characteristics of Q-switched mode-locked rectangular noise-like pulses in L-band fiber lasers.
  • Jun. 09, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 13 1314003 (2022)
  • DOI:10.3788/LOP202259.1314003
Temperature Field of Continuous LD End-Pumped YAG/Yb∶YAG Composite Crystal
Li Long, Niu Juan, Zhang Chunling, Yang Jianhua, Xue Biao, and Geng Yingge
In this paper, we proposed a finite element model of composite crystals to solve the thermal effect of disk crystal end-pumped by LD. The model was established based on the heat conduction theory, which is related to the working characteristics of continuous LD end-pumped YAG/Yb∶YAG disk. The effects of different factors such as the pump power, composite crystal thickness, and cross section size on the temperature field were analyzed by setting LD pumping parameters. The results showed that when the geometry of the composite crystal is constant, the temperature of the crystal increased with increasing pump power. At 70 W pump power, the pump spot radius was 400 μm via the collimation focusing of the optical coupling system, the thickness of Yb∶YAG crystal was 3 mm, and the thickness bonding of YAG crystal changed from 0 mm to 0.7 mm. Furthermore, the rise in maximum radial and axial temperatures decreased by 39.7 ℃ and 238.3 ℃, respectively. Under the same pumping conditions and with a 0.5 mm thick YAG crystal, the cross section radius of composite crystal increased from 8 mm to 13 mm, the maximum temperature rise along the radial and axial directions decreased by 32.8 ℃ and 171.7 ℃, respectively. Thus, the composite crystals can reduce the thermal effect inside laser crystals, which is significant for realizing high-power outputs of solid-state Yb∶YAG lasers.
  • Jun. 09, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 13 1314002 (2022)
  • DOI:10.3788/LOP202259.1314002
Surface Cleanliness Characterization of Titanium Alloy Sheet Based on Beckmann-Kirchhorff Simplified Model
Zhao Wenyuan, Liu Jianyong, and Yang Songqiu
With the industrial need of laser cleaning, new requirements are put forward for the cleanliness evaluation of material surfaces before and after cleaning. In this paper, the bidirectional reflection technology of surface roughness measurement is proposed to characterize the surface quality of materials, and the autocorrelation length (T) and the root mean square of surface roughness(σ) are taken as the key parameters to characterize the surface quality of samples. Based on the Beckmann-Kirchhorff integral scattering model and after a reasonable simplification on rough surfaces, we plot the ratio Is/I0 of the incident light intensity (I0) to the reflected light intensity (Is) versus the inverse square of wavelength (1/λ2). Under the simplified model, an ideal linear curve can be obtained in the vertical incident direction with a large g value. The parameter σg obtained by linear fitting can be used as the characterization value of surface cleanliness. In the experiment, a beam of white light (xenon lamp) is first used to irradiate the surface of the titanium alloy sheet TA15 sample at a vertical angle, and then the specular reflected light beam on the surface of the sample is collected. The experimental results confirm the correlation between the surface quality of the sample and the σg value. This method is a non-contact spectral detection method, which can realize high-speed scanning, is convenient and fast, and can be used to online judge the cleanliness after laser cleaning in practical work.
  • Jun. 09, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 11 1114006 (2022)
  • DOI:10.3788/LOP202259.1114006
Study on Threshold Value of Laser Cleaning Loose Surface Green Rust Bronzes
Cai Jingfang, Zhou Hao, Yan Ying, Wang Min, Tang Yijing, Yu Ying, Wu Laiming, and Cai Lankun
Unearthed bronzes are easily eroded by the external environment due to their perennial burial underground and different kinds of corrosion occur. The presence of "harmful rust" accelerates the corrosion of bronze substrates. Aiming at the common corrosion of loose green rust, the safe cleaning thresholds by the neodymium yttrium aluminum garnet (Nd∶YAG) laser cleaner in dry, wet, and agar gel states are investigated in this paper. The surface morphologies and compositions are characterized by the microscope, in situ Raman spectroscopy, and energy disperse spectroscopy (EDS). The results show that the cleaning threshold in wet state with short free running (SFR) pulse mode is 2.83?8.49 J/cm2. The high corrosion removal rate is obtained, which is conformed to the rule of the "no change in the appearance of cultural relics" and the "minimum intervention" in cultural relics protection.
  • Jun. 09, 2022
  • Laser & Optoelectronics Progress
  • Vol. 59 Issue 11 1114005 (2022)
  • DOI:10.3788/LOP202259.1114005