In recent years, picosecond lasers have developed rapidly and have been widely used in many fields such as precision processing, spectroscopy, ranging and medical treatment. A picosecond laser system with fiber-solid hybrid amplification is developed. Firstly, the central wavelength, polarization state and spectral width of the fiber seed source are optimized. The maximum energy can reach 100 nJ and the beam quality factor M2 is less than 1.10. Furthermore, double-end pump structure is used to amplify the optical power of the seed. The output power are 2.24 W and 10.8 W at 100 kHz and 13 MHz, respectively. The pulse width is 10.2 ps. By optimizing the design of optical path and thermal management technology, a better beam quality M2=1.2 is obtained. The research ideas and experimental results of this paper can provide an effective solution for further improving the power of amplifier.
Based on an all-fiber master oscillator power amplifier (MOPA) structure, a 1950-nm narrow-linewidth, single-mode, high peak power nanosecond pulsed fiber laser was developed. The seed source is a distributed feedback (DFB) semiconductor laser with a linewidth of 0.5 MHz. A precise and stable closed-loop temperature control technology is used to design the driving circuit of the seed laser, which ensures the stability of the laser wavelength and power, and greatly reduces the frequency and intensity noise of the laser. The continuous seed laser is modulated by an acousto-optic modulator (AOM). At the same time, the high-frequency control technology of acousto-optic modulator and cascade amplification technology are used to realize the continuous adjustable of laser pulse shape (Gaussian pulse or square wave pulse), repetition rate (1 kHz ~ 300 kHz) and pulse width (50 ns ~ 500 ns) of 2.0 μm band single frequency laser. This laser is very suitable for coherent lidar applications
Cantilever enhanced photoacoustic spectroscopy (CEPAS) technology improves the detection ability of weak gas photoacoustic signal effectively utilizing a micro-cantilever acoustic sensor instead of capacitive microphone, which can achieve highly sensitive detection of CO2 and has great significance for environmental monitoring, industrial production control and regional carbon emission monitoring and other applications. A fiber-optic Fabry-Perot (F-P) sensor with a cantilever structure is designed in this work to overcome the disadvantage of the complication of traditional mechanical cantilever photoacoustic spectroscopy system. The photoacoustic spectroscopy system is established based on the resonance enhancement of the fiber cantilever acoustic sensor with a 2.0 μm distributed feedback (DFB) laser, which combines the technologies of wavelength modulation and second-harmonic detection for measuring CO2 concentration. The experimental results show that the concentration calibration curve has a good correlation of 0.9765, and the detection limit of CO2 concentration reaches 0.044×10-6, which verifies the feasibility of the system for detecting atmospheric CO2 concentration.
The applications of femtosecond lasers are undergoing a period of explosive growth in the laser micromachining market. We demonstrated an all-normal-dispersion figure-8 mode-locked fiber oscillator using a nonlinear amplifying loop mirror, delivering laser pulses with 8.2-nJ pulse energy. The spectral bandwidth of 10 nm is realized at the repetition rate of 10 MHz. The pulse width of the chirped pulses is 6.7 ps and the output pulses can be compressed to below 200 fs. An all-normal-dispersion figure-9 laser is also presented in this letter. The repetition rate of the laser can be improved to 25.7 MHz. Owing to their compact sizes, high stability and superior self-starting ability, the all-normal-dispersion figure-8 and figure-9 lasers have the potential to be used in industrial grade femtosecond laser systems.
In this work, a novel fiber Bragg grating (FBG) sensor is designed for the measurement of motor axis transient torque. The sensing mechanism of FBG is introduced, the mathematical relationship between applied torque and Bragg wavelength is analyzed, and the theoretical model for a dual-FBG sensing structure is established. The two FBGs with different Bragg wavelengths are symmetrically attached onto the surface of the sensing axis, and used as sensing and reference elements, respectively. The structure can effectively relieve the thermal effect and eliminate environmental perturbation. After the calibration of axial torque with respect to Bragg wavelength by using a torque gauge, the measuring range of the fiber-optic torque sensor is 0~15 Nm, the sensitivity is 90.2 pm/Nm, the linearity is 0.9957, the repeatability error is 3.25 %FS, and the hysteresis error is 2.0 %FS. The torque sensing shaft is connected to the driving shaft of a stepper motor with a flexible coupling, and transient torque is obtained in real time with a frequency response bandwidth of <35 kHz, which is limited only by the readout speed of the interrogation system. This work provides a new technique for transient torque measurement of a motor.