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RSS2021 Vol. 33, No. 11
- Cover and Contents
- Feature Issue on Novel Laser Technology
- High Power Laser Physics and Technology
- Inertial Confinement Fusion Physics and Technology
- High Power Microwave Technology
- Particle Beams and Accelerator Technology
- Pulsed Power Technology
- Nuclear Science and Engineering
- Advanced Interdisciplinary Science
A mid-infrared fiber laser operating at λ≈3 μm is demonstrated using a Ho3+/Pr3+ co-doped AlF3-based glass fiber as a gain fiber. Under 1150 nm single-mode fiber laser pumping, the fixed-wavelength laser had maximum output power of 1.02 W, a slope efficiency of 10.7%, and M2≈1.2. The results prove this type of fiber is a potential gain medium for more powerful mid-infrared fiber lasers.
Due to the great application potential in various fields such as spectral beam combination, photoacoustic spectroscopy and nonlinear frequency conversion, high-power spectrum-tunable fiber lasers have gained much attention in recent years. Based on a spectrum-flexible superfluorescent fiber source and the well-known master-oscillator power amplifier structure, we have demonstrated a 3 kW linewidth- and wavelength-tunable high-power fiber laser. The output central wavelength of the fiber laser can be tuned over 1065−1085 nm, and the 3 dB linewidth is adjustable over 2.4−13.8 nm.
The recent research progress of random distributed feedback fiber lasers in the time-frequency-spatial domain is systemically reviewed in this paper. The factors influencing the time-frequency-spatial dynamic characteristics of random distributed feedback fiber lasers are analyzed and summarized. Finally, the prospects of random distributed feedback fiber lasers used in high-power laser driving facility are put forward, and the potential research area in future is discussed.
Mid-infrared (MIR) lasers have various advantages and can be widely used in either fundamental research fields or practical applications such as strong-field physics, molecular sensing and minimally-invasive tissue ablation. Generally, there are two categories of methods to generate MIR laser emission: one is direct lasing and the other is nonlinear frequency down-conversion. However, for the ultra-broadband few-cycle MIR generation, nonlinear down-conversion is the only available method. Intra-pulse Difference Frequency Generation (IP-DFG) is a simple method of nonlinear frequency conversion. In this article, the IP-DFG technology for the ultra-broadband MIR few-cycle pulses generation is reviewed. Different MIR nonlinear crystals, various driving laser sources, the spectral coverage of the MIR-IPDF output, and the conversion efficiency are compared and discussed. Last but not least, the prospects and challenges of MIR IP-DFG are presented.
Mid-infrared region ranging from 2.5 μm to 25 μm covers absorption lines of most molecules and multiple atmospheric windows. The ultrafast lasers operating in this waveband have vast applications in many fields. In recent years, significant progress has been made in the area of mid-infrared fiber-based ultrafast lasers in terms of long waveband emission and ultrafast pulse generation, which enables many unexplored reseaches and novel applications. In this paper, we reviewed the development of mid-infrared ultrafast fiber lasers over the last decade. Starting with the fiber materials and the gain medium used for mid-infrared emission, we focused on the current mode-locking methods and their representative progress for mid-infrared fiber lasers including nonlinear polarization rotation, saturable absorbers and frequency shifted feedback technique. Then we briefly discussed the mid-infrared pulse post-modification and typical applications including few-circle pulses and supercontinuum generation. Finally, the critical challenges the mid-infrared ultrafast fiber lasers are currently facing and the possible routines for further development were summarized.
An alternative approach to realizing room temperature spintronic applications is introducing spin-polarized carriers in a semiconductor laser, which is beyond the usual magnetoresistive effects. Spin lasers have been widely applied in the fields of secure optical communication, quantum computing, optical information processing, and data storage, reconfigurable optical interconnection, and biomedical sensing because the injection of spin-polarized carriers results in the rich dynamic properties of spin lasers, including high-frequency polarization oscillations and polarization chaos regimes. In this paper, the research progress of the dynamic characteristics and applications of spin lasers in recent years is reviewed. Firstly, the dynamic behavior and chaotic evolution mechanism of spin lasers are introduced. Then the high-frequency polarization oscillation characteristics of spin lasers are analyzed. Furthermore, the latest research progress of applications based on the dynamic characteristics of spin lasers is summarized. Finally, the prospects and challenges of spin lasers are expected to enlighten fundamental researches and engineering applications in the relevant fields.
Stimulated Brillouin scattering (SBS) is a third-order nonlinear process, which is phased conjugation reflected in the SBS phase conjugation mirror (SBS-PCM). Therefore, it is a very useful tool for the compensation of wavefront distortion induced by strongly thermally stressed active material, especially in high-power and high-energy lasers. To maximize the effectiveness of SBS-PCM, many research efforts have been poured in both theoretically and experimentally in the past decades. Several researchers have studied the liquid medium that is the best fit for SBS-PCM in high power laser systems; some have investigated the geometry (such as two-cell structure, choice of the optimum parameters, and the addition of a rotating wedge) of the system that will give the most appropriate desired characteristics; while some researched the impurities of the selected liquid. This work presents a review of the factors determining the performance of SBS-PCM, the applications of SBS-PCM in high power lasers, and recent scientific achievements in the SBS-PCM high power laser systems. This work is proposed as a reference and guiding manual for SBS-PCM-related experiments and research.
We demonstrated a self-starting mode-locked Ti:sapphire laser by using a synchronously pumping scheme with a frequency doubled femtosecond Yb fiber laser. By carefully adjusting the cavity length of the Ti:sapphire oscillator to match the fiber laser, the mode-locking operation can start automatically. In the experiment, a femtosecond ytterbium-doped fiber laser at 520 nm was used to pump the Ti:sapphire laser synchronously. Under the 3.4 W pump power, 130 mW/17 fs mode locked laser pulses were obtained from the Ti:sapphire laser at the repetition rate of 75 MHz. It not only solves the difficulty of conventional Ti:sapphire oscillator for no-starting mode locking, but also synchronously supplies three femtosecond laser beams at central wavelengths of 1040, 800 and 520 nm, which paved an advanced way for further studies of coherent combination and optical parametric amplification.
In this paper, the integrated mode measurement and control method based on fractional Fourier transform is proposed. The fractional Fourier transform optical system is used to modulate the spatial and phase distributions of the fiber mode coupling states so that the mode decomposition can be realized effectively. Compared with dual Fourier transform (F2) method as well as spatial and spectral imaging (S2) method, the fractional Fourier transform method adopted in this system is easier to decompose high-order modes by changing fractional order parameters, and controlling the spatial distributions of modes as well as the superposition states between modes. The mode measurement method based on the fractional Fourier transform can be studied in the spatial and phase superposition of modes in a wider range of space, and it can also be degenerated to F2 and S2 methods.
This paper proposes an all-fiber Mach-Zehnder Interference (MZI) dual-parameter sensor based on S-shaped-dislocation structure. The sensor is prepared by using fusion splicer through simple discharge and fusion splicing steps, with pieces of single-mode fibers. When the rotator is twisting clockwise, the transmission spectrum of the sensor shifts to the short wavelength direction; when it is twisting counterclockwise, the transmission spectrum shifts to the different direction. The sensor’s torsion experimental results show that the torsion direction can be distinguished, and the torsion sensitivity in the clockwise and counterclockwise rotation directions on the fiber cross-section is −223 pm/(rad·cm−1), 140 pm/(rad·cm−1), respectively. The strain sensitivity within a certain strain range is 0.145×106 dB/ε (where ε is strain), and the temperature cross sensitivity is extremely small and can be ignored. Therefore, this dual-parameter sensor based on the SMF core-cladding MZI interferometer has the advantages of high sensing sensitivity, small size, simple process, low cost, and distinguishable torsion direction. It is expected to become a good candidate instruments in many dual-parameter measurement operations.
Tapered fiber has unique advantages in suppressing nonlinear effects because its core radius increases uniformly along the length of the fiber. In this paper, the output spectrum evolution and Raman performance of three different types of passive fibers are simulated and analyzed under the input of single transverse mode Gaussian beam: the passive fibers with constant core radius, linearly increasing radius and nonlinearly increasing core radius, all have the same input core diameter of 50 μm. Under the same conditions, when the input power is 10 kW, the Raman suppression ratio (defined as the difference between the intensity of the signal peak and the Raman peak in the spectrum) of constant type passive fiber is 33.1 dB, while those of the linear type and nonlinear type are 47.0 dB and 48.6 dB, respectively, which are better than that of constant type by 13.9 dB and 15.5 dB; When the input power reaches 17.5 kW, 81.6% of the input energy of the constant type is dissipated or transferred to other wavelengths, while that of linear and nonlinear types is less than 2%, and the output signal optical band energy accounts for 98.1% and 98.9% of the total input energy. The results show that the threshold of stimulated Raman scattering can be effectively improved by using linear or nonlinear passive fiber instead of constant type, and the study can provide a useful reference for the design of high-power fiber combiner and fiber end cap.
In view of the key bottleneck that Fe2+: ZnSe laser lacks effective high-power pumping source at present, the technical route of using a continuous wave HF chemical laser to pump Fe2+: ZnSe to achieve laser output in 4 μm band is proposed. The feasibility of this technical route is investigated both experimentally and theoretically. The output of a continuous wave HF chemical laser pumped Fe2+: ZnSe laser at watt level is obtained for the first time. The output power is about 1.7 W, the central wavelength is 4.18 μm, and the lasing lasts about 2 s.
To establish the effective evaluation about damage properties of large-aperture and high-energy optic components, we studied the statistics of the surface damage of the DKDP component. We analysed and summarized various kinds of damage distributing in surface of the optic component by step-by-step shooting, merging images and counting damage pits. We investigated correlation distribution of damage types and irradiation conditions using statistics of surface damage data, theoretical calculation and demonstration of similar experiment. It is found that positions of damage pits are closely relevant to distribution of energy density of laser beam (3ω). When the energy density exceeds 6.7 J/cm2, the distribution of energy density of the laser beam can be Gaussian. On the contrary, when energy density is less than 6.7 J/cm2, the distribution of energy density of the laser beam can be uniform. Our study could provide a valuable reference for evaluating characteristics of damage to optical component working under irradiation in large-aperture high-energy laser. It is also reterable in operating and maintaining large-aperture high-energy laser facility.
Temperature has an important influence on the performance index and working life of distributed feedback (DFB) laser. Aiming at the laser application in a wide temperature range, the research status and trend of laser temperature control system are analyzed, and the design principle is given. A simulated temperature control and detection system of DFB laser is developed by using linear drive and PID closed-loop control method and simulator, and the system is used to verify the 1550 nm DFB laser. The results show that the system could work for a long time (≥2 h) in the full temperature range of −55 ℃−70 ℃, the working state of the laser was stable, and the central wavelength did not drift. The temperature control precision of the system varies with the temperature range of the working environment. It can reach ±0.02 ℃ at room temperature within ±0.8 ℃ in the full temperature range, and the tracking error is less than ±0.5 dB. Compared with the traditional laser temperature control system, the system has wider working temperature range, higher control precision, smaller volume, and lower cost, being simple and reliable. For the application of DFB laser with strict temperature environment requirements, it has important engineering practical significance.
The hot image effect of the high power laser system may cause the peak power of the beam to increase drastically, and the amplifying Keer medium will make this increase in light intensity more intense. When the input beam power is strong enough, the gain saturation effect of the amplifying Keer medium on the beam is more obvious. Based on the Fresnel-Kirchhoff diffraction theory and the nonlinear paraxial wave equation, the hot image generation process of the intense laser in the gain saturation region of the amplifying Keer medium is theoretically analyzed, and the gain saturation part of the beam transmission equation is subjected to the Maclaurin expansion for approximation. After deriving the analytical formula of hot image intensity and hot image position when the medium is thin, the hot image intensity and position predicted by the analytical conclusion are verified by numerical simulation. The simulation results show that the position of the hot image is symmetrical to the diffracted object with respect to the medium, and the analysis results of hot image intensity are consistent with the simulation results. The intensity of the hot image stops increasing as the nonlinear effect of the nonlinear medium increases. In addition, the change of the intensity of the hot image with the obscuration type is discussed.
This paper uses the two-dimensional particle-in-cell simulation program EPOCH to verify the feasibility of the relativistic electron beam probe in diagnosing the electrostatic wave generated by stimulated Raman scattering. The results show that the electron beam probe will produce density modulation in the transverse direction of the electron beam probe after passing through the electrostatic wave’s electric field. The density modulation is periodically distributed and moves along the propagation direction of the electrostatic wave. The wavenumber of the density modulation corresponds to the wavenumber of the electrostatic wave. And the moving speed corresponds to the phase speed of the electrostatic wave, so it can be used to deduce the temperature and density of electrons under certain conditions. In the process of diagnosing electrostatic waves, the beam length of the electron beam probe must be shorter than the wavelength of the electrostatic wave or the exposure time of the diagnostic equipment must be less than the period of the electrostatic wave. The research in this paper provides a new method of directly diagnosing the temperature and density of electrostatic waves and electrons, which is of great significance for promoting the experimental research of stimulated Raman scattering and other laser plasma instabilities.
The high-frequency slow-wave structure of 2−18 GHz ultra-wideband traveling-wave tube (TWT) is studied and analyzed to meet the requirements of modern information warfare for TWT. Based on the traditional wideband TWT, the positive dispersion characteristics of non-fin loading section were introduced to realize the 2−18 GHz ultra-wideband high-frequency slow wave structure, with the maximum bandwidth of 9∶1. Results show that the output power of fundamental wave is up to 100 W, the second harmonic suppression ratio is better than −3 dBc in the full frequency band, and the second harmonic suppression ratio is better than −5 dBc at 2 GHz, which provides a theoretical basis for the design of ultra-wideband high-power devices. At the same time, the spiral pitch at the output end is adjusted to a positive gradient distribution to further optimize the low frequency secondary wave suppression ratio and improve the saturation output power of the high frequency band.
To verify whether the parameters of the domestic proton injector meet the requirements, a beam diagnostic system was designed to measure the current, emittance, energy and energy spread of the domestic proton linear injector beam. This beam diagnostic system has the main functions of measuring the emittance by variable focus method and measuring beam energy and energy spread by analyzing magnet. The beam transport line design software Tracewin (version 2.11.4.1) was used to design the physical system beam line, and the accuracy of the beam diagnostic system to measure the emittance and energy of the proton beam was simulated and calculated. Since the beam accelerated by RFQ-(APF)DTL is a “trailing” non-ideal bunch , it is necessary to analyze the influence of the non-ideal bunch on the emittance and energy measurement of the beam diagnostic system. The analysis of the simulation calculation results shows that compared with the ideal bunch, the non-ideal bunch has greater impact on emittance measurement accuracy and smaller impact on energy measurement accuracy of the beam diagnostic system.
A new kind of sensor Turbo-ICT has been applied to accurate bunch charge measurement in BEPCII transportation line. The system improves the resistance ability against external interference and has high signal-to-noise ratio. This paper introduces the principle, the design ideas and the function of the system. Up to now, Turbo-ICT has been used to operate online for electron bunch charge quantity measurements successfully. This paper also presents the experiment results of the sensor.
As the key component of the electromagnetic pulse simulator for steepening pulse output, the peaking capacitor is prone to surface discharge and breakdown in practical engineering applications. The photoelectric detection system can effectively analyze the surface discharge of insulation. Aiming at the technical problem of surface discharge monitoring of peaking capacitor, a set of photoelectric detection system for insulation surface discharge process is developed to detect the phenomenon of insulation surface discharge. Firstly, the design scheme of photoelectric detection system for dielectric surface discharge process is proposed. Secondly, the delay performance of the system is evaluated. Finally, the experiment of locating the surface discharge process of dielectric is completed, which verifies the feasibility of the photoelectric detection system. Experiments show that the system can effectively locate the discharge area.
To meet the demand of irreversible electroporation for nanosecond pulse power supply, this paper proposes a sub-microsecond high voltage pulse power supply with high repetition frequency, which is based on positive Marx circuit and has ns rising time. The pulse power supply uses optical fiber to transmit signals. After the driver chip amplifies the signal, the magnetic core transformer is used to transmit the drive signal to the MOSFET. The magnetic core transformer provides magnetic isolation to the circuit, so that the drive circuit will not be affected by the high voltage output and the withstand voltage level of the circuit is improved. The design of drive circuit is simple, and it requires fewer components. It provides negative bias voltage so that the switch can be reliably turned off and can effectively improve the electromagnetic compatibility. A 16-stage prototype has been built. The experiment showed that 10 kV square pulses were obtained over 10 kΩ resistive load when the input voltage was 630 V. Its minimum pulse width is 300 ns, and the frequency is adjustable from 1 Hz to 10 kHz. The pulse power supply is compact, and can flexibly adjust the voltage amplitude, pulse width and frequency. The influence of the magnetic material and number of turns of the windings of the magnetic core are also studied. The increase of turns ratio will affect the signal pulse width. Under certain conditions, the difference of single turn inductance and magnetic core material have little effect on signal pulse width.
Applying series and parallel structure, a high current pulse generator was designed with thyristor. By analyzing the conducting current in circuit, the self triggering principle of the pulse generator is described. The variation of magnetic field in lens excited by output pulse current is simulated. The output characteristics of the circuit were measured. Using capacitors with parameters of 600 V/2200 μF and DC voltage of 550 V, under load resistance of 6 Ω and load inductance of 31.5 MH, a pulse with amplitude of −2.1 kV, FWHM of 7.34 ms, and pulse front of 450 ns was obtained. The pulse current is −225 A in amplitude, 6.3 ms in FWHM, 4.11 ms in pulse front.
To solve the problem of selecting shape and size of the pinhole in the full-field X-ray fluorescence (XRF) imaging, the Geant4 Monte Carlo simulation software was used to simulate pinholes of 6 different types and 4 different diameters. The effects of the parameters on the spatial resolution which referred to the point spread function and the modulation transfer function were analyzed. The imaging process of different energy fluorescence X-ray plane sources is simulated, and the performance of image processing was analyzed by mean filter and the Richardson iteration method. The simulation results show that the pinhole model of the double conical-hole combined with the straight-hole has better sharpness and isoplanatism of the point spread function, a higher cut-off frequency of modulation transmission function, and better spatial resolution for X-ray of the energy less than 20 keV, which meant it is more suitable for full-field XRF imaging; the algorithm of mean filtering combined with the Richardson iteration performs better in full-field XRF image processing.
Surface-enhanced Raman spectroscopy (SERS) technology has been widely used in viral molecular detection due to its high sensitivity, simple operation and rapid detection. The research of virus detection by Raman technology at home and abroad mainly focuses on the detection of the SERS spectrum of viral nucleic acids and various bases that make up the nucleic acids, and detection of viral proteins is rare. In this paper, the S protein of the new coronavirus (SARS-CoV-2) is used as the detection object, and with the label-free SERS detection method, the ordinary Raman spectra of solid and saturated liquid S protein of the SARS-CoV-2 and the SERS spectra of the low-concentration S protein of SARS-CoV-2 on the substrate of gold nanoparticles with a size of 40 nm are compared. The results show that it is completely feasible to use SERS technology to detect the S protein of SARS-CoV-2 on the substrate of 40 nm gold nanoparticles. The carboxyl groups in the S protein molecule of SARS-CoV-2 and gold nanoparticles are molecularly enhanced, and the amino groups and gold nanoparticles are electromagnetically enhanced, so that the Raman effect of the S protein of the SARS-CoV-2 is enhanced and the peak position is moved to a certain extent. The experiments obtained relatively good SERS spectra of the low-concentration S protein of SARS-CoV-2, which provides a method for the establishment of a sensitive, specific and rapid detection technology for the S protein of the SARS-CoV-2.
