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RSS2020 Vol. 32, No. 1
Recommend Articles
2020, 32: 011003.
doi: 10.11884/HPLPB202032.190469
2020, 32: 011007.
doi: 10.11884/HPLPB202032.190480
2020, 32: 011008.
doi: 10.11884/hplpb202032.190466
2020, 32: 011009.
doi: 10.11884/HPLPB202032.190451
Display Method:
2020,
32: 1-2.
2020,
32: 011003.
doi: 10.11884/HPLPB202032.190469
Abstract:
Beam precise control is the basic requirement of Interial Confinement Fusion (ICF) research for laser facility. Its technical characteristics determine that it is a system project for laser facility. This paper introduces the important progress made by the Laser Fusion Research Center of Chinese Academy of Engineering Physics in the control of focal-plane irradiance, pulse precision shaping, beam near-field intensity and novel beam exploration in recent years.
Beam precise control is the basic requirement of Interial Confinement Fusion (ICF) research for laser facility. Its technical characteristics determine that it is a system project for laser facility. This paper introduces the important progress made by the Laser Fusion Research Center of Chinese Academy of Engineering Physics in the control of focal-plane irradiance, pulse precision shaping, beam near-field intensity and novel beam exploration in recent years.
2020,
32: 011004.
doi: 10.11884/HPLPB202032.190427
Abstract:
The instability of the laser plasma interaction is expected to be greatly suppressed by reducing the coherence of the output pulse of the high-power laser facilities. Using the low-coherence light as the seed source and the Nd:glass as the amplifying medium, the first kJ low-coherence broadband laser was developed delivering 960 J pulses centered at 1 056 nm with a bandwidth of 13 nm. The output pulse has a coherence time of 300 fs and a pulse duration adjustable from 3 ns to 10 ns. The spectrum of laser pulse is smooth with no longitudinal mode structure. And the spectral phase is randomly distributed, which can realize uncorrelated tunable output of pulse waveform and spectral shape. This facility successfully demonstrates the unit and system integration technologies of the broadband low-coherence laser driver and provides a new experimental platform for laser plasma interaction and high energy density physics research.
The instability of the laser plasma interaction is expected to be greatly suppressed by reducing the coherence of the output pulse of the high-power laser facilities. Using the low-coherence light as the seed source and the Nd:glass as the amplifying medium, the first kJ low-coherence broadband laser was developed delivering 960 J pulses centered at 1 056 nm with a bandwidth of 13 nm. The output pulse has a coherence time of 300 fs and a pulse duration adjustable from 3 ns to 10 ns. The spectrum of laser pulse is smooth with no longitudinal mode structure. And the spectral phase is randomly distributed, which can realize uncorrelated tunable output of pulse waveform and spectral shape. This facility successfully demonstrates the unit and system integration technologies of the broadband low-coherence laser driver and provides a new experimental platform for laser plasma interaction and high energy density physics research.
2020,
32: 011005.
doi: 10.11884/HPLPB202032.190463
Abstract:
In this paper, we demonstrate an all-fiber high-power Yb-doped 1 030 nm fiber laser based on master oscillator power amplifier structure. The record output power at 1 030 nm up to 3 004 W was achieved, along with a slope efficiency of 69.27%, which is the highest output power for 1030 nm near diffraction limited beam quality fiber laser. The beam quality factor is Mx2＝1.169, My2＝1.174, and full width at half maximum is 0.18 nm at maximum power level. The amplified spontaneous emission (ASE) suppression ratio reaches up to 37 dB.
In this paper, we demonstrate an all-fiber high-power Yb-doped 1 030 nm fiber laser based on master oscillator power amplifier structure. The record output power at 1 030 nm up to 3 004 W was achieved, along with a slope efficiency of 69.27%, which is the highest output power for 1030 nm near diffraction limited beam quality fiber laser. The beam quality factor is Mx2＝1.169, My2＝1.174, and full width at half maximum is 0.18 nm at maximum power level. The amplified spontaneous emission (ASE) suppression ratio reaches up to 37 dB.
2020,
32: 011006.
doi: 10.11884/HPLPB202032.200004
Abstract:
We demonstrated a narrow linewidth linearly polarized all-fiber laser operating at maximum output power of 3.08 kW with a 3 dB linewidth of 0.2 nm based on a simple master oscillator power amplifier (MOPA) structure. The polarization extinction ratio (PER) is about 94% and the M 2 is about 1.4 along the whole power scaling process. This is the first demonstration of a 3 kW linearly polarized all-fiber laser output. Compared with the narrow linewidth fiber amplifier based on phase modulation, this system can achieve a nearly same linewidth. Meanwhile, it has the characteristics of high stimulated Brillouin scattering (SBS) threshold, simple structure, and low cost, etc.
We demonstrated a narrow linewidth linearly polarized all-fiber laser operating at maximum output power of 3.08 kW with a 3 dB linewidth of 0.2 nm based on a simple master oscillator power amplifier (MOPA) structure. The polarization extinction ratio (PER) is about 94% and the M 2 is about 1.4 along the whole power scaling process. This is the first demonstration of a 3 kW linearly polarized all-fiber laser output. Compared with the narrow linewidth fiber amplifier based on phase modulation, this system can achieve a nearly same linewidth. Meanwhile, it has the characteristics of high stimulated Brillouin scattering (SBS) threshold, simple structure, and low cost, etc.
2020,
32: 011007.
doi: 10.11884/HPLPB202032.190480
Abstract:
Ordered motion of quantum particles produces laser, while disordered motion produces heat, this conflict overwhelms development of high energy laser since its beginning, and the guide-line of its history is just a battle with waste heat. Reviewing the 60-year development of high energy laser and examining the science behind it, we divided its history into pre and past 30 years, which separately solved the problem of capability and was just solving the problem of easy-to-use ability. Sticking with heat generation and dissipation, we discussed inner links between power, beam quality and efficiency of high energy laser, reviewed the rise and fall of different kinds of lasers, and predicted future development of high energy laser.
Ordered motion of quantum particles produces laser, while disordered motion produces heat, this conflict overwhelms development of high energy laser since its beginning, and the guide-line of its history is just a battle with waste heat. Reviewing the 60-year development of high energy laser and examining the science behind it, we divided its history into pre and past 30 years, which separately solved the problem of capability and was just solving the problem of easy-to-use ability. Sticking with heat generation and dissipation, we discussed inner links between power, beam quality and efficiency of high energy laser, reviewed the rise and fall of different kinds of lasers, and predicted future development of high energy laser.
2020,
32: 011008.
doi: 10.11884/hplpb202032.190466
Abstract:
Plasma optics is an important way for the development of high power laser technology because plasma medium has high energy storage density, no laser-induced damage threshold and rich optical properties. The research status of plasma optics in recent years is introduced, and the development trend of plasma optics in the future is discussed.
Plasma optics is an important way for the development of high power laser technology because plasma medium has high energy storage density, no laser-induced damage threshold and rich optical properties. The research status of plasma optics in recent years is introduced, and the development trend of plasma optics in the future is discussed.
2020,
32: 011009.
doi: 10.11884/HPLPB202032.190451
Abstract:
As widely used in military, medicine, communication, processing and other fields, femtosecond laser has become a research hotspot of the whole laser technology in the 21st century. The pump source used by laser diodes (LDS) has become a new development trend of all-solid-state femtosecond lasers owe to the rapid development of LDs. Yb3＋-doped laser crystal materials gradually become important gain media for LD pumping and generate 1.0 μm femtosecond laser due to their unique energy level structures, broad absorption and emission spectra. In this paper, the research progress of Yb3＋-doped femtosecond laser crystals is summarized in detail, the main problems are analyzed, and two directions for the development of femtosecond laser crystals in the future are proposed: high efficiency and low power femtosecond laser, high power and high energy femtosecond laser. The crystal growth, spectra properties, continuous and femtosecond laser performances of the Yb3＋:Sr3Y2(BO3)4 crystal were studied in detail. And the Yb3＋:Sr3Y2(BO3)4 femtosecond laser with the center wavelength of 1060 nm, pulse width of 116 fs, average output power of 1.08 W and optical conversion efficiency of 33.1% were successfully generated. The experimental results indicate that Yb3＋:Sr3Y2(BO3)4 and its corresponding system crystals are excellent femtosecond laser materials with high optical conversion efficiency.
As widely used in military, medicine, communication, processing and other fields, femtosecond laser has become a research hotspot of the whole laser technology in the 21st century. The pump source used by laser diodes (LDS) has become a new development trend of all-solid-state femtosecond lasers owe to the rapid development of LDs. Yb3＋-doped laser crystal materials gradually become important gain media for LD pumping and generate 1.0 μm femtosecond laser due to their unique energy level structures, broad absorption and emission spectra. In this paper, the research progress of Yb3＋-doped femtosecond laser crystals is summarized in detail, the main problems are analyzed, and two directions for the development of femtosecond laser crystals in the future are proposed: high efficiency and low power femtosecond laser, high power and high energy femtosecond laser. The crystal growth, spectra properties, continuous and femtosecond laser performances of the Yb3＋:Sr3Y2(BO3)4 crystal were studied in detail. And the Yb3＋:Sr3Y2(BO3)4 femtosecond laser with the center wavelength of 1060 nm, pulse width of 116 fs, average output power of 1.08 W and optical conversion efficiency of 33.1% were successfully generated. The experimental results indicate that Yb3＋:Sr3Y2(BO3)4 and its corresponding system crystals are excellent femtosecond laser materials with high optical conversion efficiency.
2020,
32: 011010.
doi: 10.11884/HPLPB202032.190456
Abstract:
To control the thermal wavefront distortion of repetition frequency laser, we′ve developed a water-cooled active-mirror laser amplifier, which was uniformly cooled from the rear of crystal disk. The numerical anslysis and experimental study on the characterstics of the amplifier’s thermal distortion were carried out. It was found that the thermal distorition devoted a significiant modulation to the near field of the laser when the average pump power density was as high as 200 W/cm2 with the operation frequency of 10 Hz. Near-field modulation would bring a risk to damage the amplifier. To eliminate the modulation of thermal distortion in the near field, two approaches were taken. Firstly, the pump intensity distribution was homogenized, then the edge thermal balance control was carried out. The near field modulation from thermal wavefront distortion was eliminated by these means, a four-pass amplifier with water-cooled laser heads ran well at 10 Hz. The focal spot of output laser was smaller than 5 diffraction limits without any compensation.
To control the thermal wavefront distortion of repetition frequency laser, we′ve developed a water-cooled active-mirror laser amplifier, which was uniformly cooled from the rear of crystal disk. The numerical anslysis and experimental study on the characterstics of the amplifier’s thermal distortion were carried out. It was found that the thermal distorition devoted a significiant modulation to the near field of the laser when the average pump power density was as high as 200 W/cm2 with the operation frequency of 10 Hz. Near-field modulation would bring a risk to damage the amplifier. To eliminate the modulation of thermal distortion in the near field, two approaches were taken. Firstly, the pump intensity distribution was homogenized, then the edge thermal balance control was carried out. The near field modulation from thermal wavefront distortion was eliminated by these means, a four-pass amplifier with water-cooled laser heads ran well at 10 Hz. The focal spot of output laser was smaller than 5 diffraction limits without any compensation.
2020,
32: 011011.
doi: 10.11884/HPLPB202032.190479
Abstract:
The initial damage and damage growth of fused silica optical elements irradiated by 3ω alone, by two wavelengths (3ω＋2ω and 3ω＋1ω) at the same time were studied. When the energy density of 3ω is near its threshold, the influence of 2ω and 1ω of low energy density on the initial damage and damage growth is studied. The energy coupling mechanism between wavelengths is analyzed. The results show that: When the energy density of 2ω or 1ω is much lower than its threshold, irradiating at the same time, their effects on the initial damage probability and damage growth threshold can be ignored. But the initial damage degree and damage growth coefficient will increase. The measurement of shock wave velocity based on femtosecond dual pulse imaging shows that, when 3ω and 1ω irradiate at the same time, the energy coupling effect between wavelengths will promote the deposition efficiency of laser energy to materials.
The initial damage and damage growth of fused silica optical elements irradiated by 3ω alone, by two wavelengths (3ω＋2ω and 3ω＋1ω) at the same time were studied. When the energy density of 3ω is near its threshold, the influence of 2ω and 1ω of low energy density on the initial damage and damage growth is studied. The energy coupling mechanism between wavelengths is analyzed. The results show that: When the energy density of 2ω or 1ω is much lower than its threshold, irradiating at the same time, their effects on the initial damage probability and damage growth threshold can be ignored. But the initial damage degree and damage growth coefficient will increase. The measurement of shock wave velocity based on femtosecond dual pulse imaging shows that, when 3ω and 1ω irradiate at the same time, the energy coupling effect between wavelengths will promote the deposition efficiency of laser energy to materials.
2020,
32: 011012.
doi: 10.11884/HPLPB202032.190454
Abstract:
Conjugate rotation smoothing scheme for laser quad based on dual-frequency laser and spiral phase plate was proposed. The dual-frequency laser provides frequency shift among the beamlets, the spiral phase plates with same helical charge but opposite sign transform the beamlets into Laguerre-Gaussian beams, and the polarization control is applied to make these beamlets coherently superposed on the target plane. On this basis, the conjugate continuous phase plates are adopted to enable the beamlets with different central wavelength and orthogonal polarization form focal spots with rapid rotation. Moreover, the spatiotemporal focal spot of the laser quad looks like conjugate spin light because of the frequency beats. It is indicated that, the scheme enables the fine-scale speckles within the focal spot rotate in a period of a few picoseconds, and even exhibit different intensities and wavelengths at different time and different positions. Hence, the novel scheme can effectively smooth the irradiation uniformity of the laser quad and even has the potential to mitigate laser plasma interactions.
Conjugate rotation smoothing scheme for laser quad based on dual-frequency laser and spiral phase plate was proposed. The dual-frequency laser provides frequency shift among the beamlets, the spiral phase plates with same helical charge but opposite sign transform the beamlets into Laguerre-Gaussian beams, and the polarization control is applied to make these beamlets coherently superposed on the target plane. On this basis, the conjugate continuous phase plates are adopted to enable the beamlets with different central wavelength and orthogonal polarization form focal spots with rapid rotation. Moreover, the spatiotemporal focal spot of the laser quad looks like conjugate spin light because of the frequency beats. It is indicated that, the scheme enables the fine-scale speckles within the focal spot rotate in a period of a few picoseconds, and even exhibit different intensities and wavelengths at different time and different positions. Hence, the novel scheme can effectively smooth the irradiation uniformity of the laser quad and even has the potential to mitigate laser plasma interactions.
2020,
32: 011013.
doi: 10.11884/HPLPB202032.190458
Abstract:
High-repetition-rate laser pulses with large pulse energies have great application potential in various areas including telecommunications, sensing, material processing, etc. Here, we report the linear and nonlinear optical properties of solution-based transition-metal dichalcogenide NbSe2 nanoparticles, and at the same time its application to mode-locked 2 μm fiber laser. The linear absorption of the NbSe2 nanoparticles covers the near-infrared to the near mid-infrared regions, and decreases with increasing wavelength, showing a broadband operation potential. Nonlinear absorption measurement of the NbSe2 nanoparticle gives a modulation depth of 6.5% and saturable intensity of 19 MW·cm−2 at the wavelength of about 2 μm. The the NbSe2 nanoparticles were transferred onto a gold mirror to fabricate a saturable absorber, with which a mode-locked thulium fiber laser was constructed and harmonic mode-locking was achieved. The mode-locked laser provides pulse energy of 3.36 nJ, pulse duration of 1.48 ns and repetition rate of 50.66 MHz. The laser wavelength is centered at 1 910.8 nm with a spectral bandwidth of 5.8 nm. The realization of dissipative-soliton mode-locking in the 2 μm fiber laser with NbSe2 nanoparticles proves that NbSe2 nanoparticles are good modulators for pulse generation in the 2 μm spectral region, and the integratable solution based nanoparticles hvae the potential of being new broadband nonlinear light modulators.
High-repetition-rate laser pulses with large pulse energies have great application potential in various areas including telecommunications, sensing, material processing, etc. Here, we report the linear and nonlinear optical properties of solution-based transition-metal dichalcogenide NbSe2 nanoparticles, and at the same time its application to mode-locked 2 μm fiber laser. The linear absorption of the NbSe2 nanoparticles covers the near-infrared to the near mid-infrared regions, and decreases with increasing wavelength, showing a broadband operation potential. Nonlinear absorption measurement of the NbSe2 nanoparticle gives a modulation depth of 6.5% and saturable intensity of 19 MW·cm−2 at the wavelength of about 2 μm. The the NbSe2 nanoparticles were transferred onto a gold mirror to fabricate a saturable absorber, with which a mode-locked thulium fiber laser was constructed and harmonic mode-locking was achieved. The mode-locked laser provides pulse energy of 3.36 nJ, pulse duration of 1.48 ns and repetition rate of 50.66 MHz. The laser wavelength is centered at 1 910.8 nm with a spectral bandwidth of 5.8 nm. The realization of dissipative-soliton mode-locking in the 2 μm fiber laser with NbSe2 nanoparticles proves that NbSe2 nanoparticles are good modulators for pulse generation in the 2 μm spectral region, and the integratable solution based nanoparticles hvae the potential of being new broadband nonlinear light modulators.
2020,
32: 011014.
doi: 10.11884/HPLPB202032.190460
Abstract:
To make full use of the long pump time of krypton fluoride excimer laser amplifiers and to increase the amplification efficiency, we carried out experimental research on multi-pulse amplification and beam combination of ultra-short UV pulses. The effect of delay time on pulse energy was studied using dual pulse amplification. Based on the above relationship, optimal delay time was confirmed, the increase of total energy and the reduction of amplified spontaneous emission (ASE) were both archived. Amplification of four ultraviolet pulses was achieved, and the energy was nearly four times that of the single pulse amplification. We also explored beam combining technology of ultraviolet ultra-short laser pulses, and combined two sub-picosecond pulses accurately.
To make full use of the long pump time of krypton fluoride excimer laser amplifiers and to increase the amplification efficiency, we carried out experimental research on multi-pulse amplification and beam combination of ultra-short UV pulses. The effect of delay time on pulse energy was studied using dual pulse amplification. Based on the above relationship, optimal delay time was confirmed, the increase of total energy and the reduction of amplified spontaneous emission (ASE) were both archived. Amplification of four ultraviolet pulses was achieved, and the energy was nearly four times that of the single pulse amplification. We also explored beam combining technology of ultraviolet ultra-short laser pulses, and combined two sub-picosecond pulses accurately.
2020,
32: 011015.
doi: 10.11884/HPLPB202032.190468
Abstract:
A kind of all-optical control method based on the deposition of graphene oxide dispersion in long period fiber grating is proposed and experimentally validated. Pumped by an external vertical light, graphene oxide generates heat and changes the phase difference of the cladding mode of long-period fiber grating. Due to the effect of thermal expansion, the grating period of the part covered by graphene oxide is changed, which makes the resonance spectrum shift. The maximum modulation depth can reach 10.6 dB, and the maximum resonance spectrum can be red-shifted by 12.8 nm. It is found that the number of times to deposit graphene oxide dispersion with the same concentration influences the experimental results. By depositing graphene oxide dispersion at the same position of the same grating once and three times respectively, it is found that the more uniform graphene oxide film can be obtained on the surface of optical fiber by three times of deposition, which enhances the interaction between light and graphene oxide, and has higher modulation efficiency and tuning efficiency. Finally, the time response test is carried out, and the response speed of the long period fiber grating after three times of deposition can reach 0.61 ms. It is found that the graphene oxide dispersion can be deposited more evenly on the surface of the optical fiber, thus obtaining greater thermal conductivity.
A kind of all-optical control method based on the deposition of graphene oxide dispersion in long period fiber grating is proposed and experimentally validated. Pumped by an external vertical light, graphene oxide generates heat and changes the phase difference of the cladding mode of long-period fiber grating. Due to the effect of thermal expansion, the grating period of the part covered by graphene oxide is changed, which makes the resonance spectrum shift. The maximum modulation depth can reach 10.6 dB, and the maximum resonance spectrum can be red-shifted by 12.8 nm. It is found that the number of times to deposit graphene oxide dispersion with the same concentration influences the experimental results. By depositing graphene oxide dispersion at the same position of the same grating once and three times respectively, it is found that the more uniform graphene oxide film can be obtained on the surface of optical fiber by three times of deposition, which enhances the interaction between light and graphene oxide, and has higher modulation efficiency and tuning efficiency. Finally, the time response test is carried out, and the response speed of the long period fiber grating after three times of deposition can reach 0.61 ms. It is found that the graphene oxide dispersion can be deposited more evenly on the surface of the optical fiber, thus obtaining greater thermal conductivity.
2020,
32: 011016.
doi: 10.11884/HPLPB202032.190453
Abstract:
This paper presents a theoretical investigation of the phase jump of multiphoton harmonic emission driven by two frequency-comb fields. The Floquet theorem is employed to provide a nonperturbative and exact treatment of the interaction between a quantum system and frequency-comb fields. Multiple multiphoton-transition paths for the harmonic emission are coherently summed. The phase information about paths can be extracted via the Fourier Transform analysis of the harmonic signals which oscillate as a function of the relative phase between two frequency-comb fields. Phase jumps were observed when harmonic emission was sweeping across the resonance by varying the frequency or intensity of two frequency-comb fields, which allows us to observe the Stark-shifted transition energy of resonant frequency of quantum system driven by strong laser fields.
This paper presents a theoretical investigation of the phase jump of multiphoton harmonic emission driven by two frequency-comb fields. The Floquet theorem is employed to provide a nonperturbative and exact treatment of the interaction between a quantum system and frequency-comb fields. Multiple multiphoton-transition paths for the harmonic emission are coherently summed. The phase information about paths can be extracted via the Fourier Transform analysis of the harmonic signals which oscillate as a function of the relative phase between two frequency-comb fields. Phase jumps were observed when harmonic emission was sweeping across the resonance by varying the frequency or intensity of two frequency-comb fields, which allows us to observe the Stark-shifted transition energy of resonant frequency of quantum system driven by strong laser fields.
2020,
32: 011017.
doi: 10.11884/HPLPB202032.190481
Abstract:
The dissipative solitons with high stability and wide spectrum are obtained from a simple and all fiber hybrid passively mode-locked erbium-doped fiber laser. The laser combines two mode-locked mechanisms of saturable absorber and nonlinear polarization rotation, and operates in the normal dispersion region. Through dispersion management, the laser can generate a series of soliton pulses with spectral width of 39.1 nm and pulse duration of 178 fs. The wavelength of laser operation is 1.55 μm, the repetition frequency is about 34.3 MHz, and single pulse energy is evaluated to be 0.33 nJ. At the same time, the laser also possesses the slope efficiency of about 15.5%; at room temperature, the laser can realize self-starting mode locking, and the operation time in the stable state of a single pulse output is more than 15 h.
The dissipative solitons with high stability and wide spectrum are obtained from a simple and all fiber hybrid passively mode-locked erbium-doped fiber laser. The laser combines two mode-locked mechanisms of saturable absorber and nonlinear polarization rotation, and operates in the normal dispersion region. Through dispersion management, the laser can generate a series of soliton pulses with spectral width of 39.1 nm and pulse duration of 178 fs. The wavelength of laser operation is 1.55 μm, the repetition frequency is about 34.3 MHz, and single pulse energy is evaluated to be 0.33 nJ. At the same time, the laser also possesses the slope efficiency of about 15.5%; at room temperature, the laser can realize self-starting mode locking, and the operation time in the stable state of a single pulse output is more than 15 h.
2020,
32: 011018.
doi: 10.11884/HPLPB202032.190265
Abstract:
We apply laser-driven launching technique to the interaction between high-velocity metal granule and gas to investigate high speed gas-solid two-phase flow transport. Optimization of target design and adjustment of laser parameters were used to control the laser-driven process. Diagnostic tools with high resolving power of space and time as well as higt accuracy were set up to capture the high-velocity granule. The unsteady flow field of the granule was simulated by solving the the 3-D Reynolds averaged Navier-Stokes equations and six degree of freedom ballistic equation. With the implicit Gauss-Seidel scheme, the code was advanced in time. The results indicated that the laser-driven launching technique was effective and the shadow photographs of high-velocity granule were taken successfully. The aerodynamic drag of high-velocity granule was computed with numerical simulation.
We apply laser-driven launching technique to the interaction between high-velocity metal granule and gas to investigate high speed gas-solid two-phase flow transport. Optimization of target design and adjustment of laser parameters were used to control the laser-driven process. Diagnostic tools with high resolving power of space and time as well as higt accuracy were set up to capture the high-velocity granule. The unsteady flow field of the granule was simulated by solving the the 3-D Reynolds averaged Navier-Stokes equations and six degree of freedom ballistic equation. With the implicit Gauss-Seidel scheme, the code was advanced in time. The results indicated that the laser-driven launching technique was effective and the shadow photographs of high-velocity granule were taken successfully. The aerodynamic drag of high-velocity granule was computed with numerical simulation.
2020,
32: 011019.
doi: 10.11884/HPLPB202032.190277
Abstract:
The effect of pump homogenization on the beam quality of the output laser is studied for a compact partially end-pumped hybrid-cavity slab laser amplifier, i.e. Innoslab laser amplifier. Using ZEMAX simulation software, two pump coupling modes, direct imaging and homogenization with waveguide were designed, and their effects on the uniformity of light intensity distribution in the slow axis (crystal width) direction of laser diode arrays were compared. It is found that the pump uniformity is significantly improved after the waveguide is homogenized and the influence of the laser diode array luminescence dead pixels on the pump imaging is weakened. Furthermore, the effect of pumping homogenization on the performance of Innoslab laser amplifier is verified by experiments: the uniformity of slow-axis pumping increases from 90.6% to 95.4% after homogenization with waveguide, and the quality of output laser beam M2 increases from 2.41 to 1.55 after three-pass amplification, and the self-oscillation in the cavity is effectively suppressed.
The effect of pump homogenization on the beam quality of the output laser is studied for a compact partially end-pumped hybrid-cavity slab laser amplifier, i.e. Innoslab laser amplifier. Using ZEMAX simulation software, two pump coupling modes, direct imaging and homogenization with waveguide were designed, and their effects on the uniformity of light intensity distribution in the slow axis (crystal width) direction of laser diode arrays were compared. It is found that the pump uniformity is significantly improved after the waveguide is homogenized and the influence of the laser diode array luminescence dead pixels on the pump imaging is weakened. Furthermore, the effect of pumping homogenization on the performance of Innoslab laser amplifier is verified by experiments: the uniformity of slow-axis pumping increases from 90.6% to 95.4% after homogenization with waveguide, and the quality of output laser beam M2 increases from 2.41 to 1.55 after three-pass amplification, and the self-oscillation in the cavity is effectively suppressed.
2020,
32: 011020.
doi: 10.11884/HPLPB202032.190274
Abstract:
For high-power laser devices using off-axis multi-pass amplification technology, the technology to suppress self-oscillation is of great research value. It is found in engineering practice that the surface of the structure near the aperture of the main amplification system is relatively bright, thus when the amplifier is working, with sufficient gain, a resonant cavity is formed between the bright structural surface and the cavity mirror to generate self-oscillation and ablation. In this paper, this problem of the device is studied by using Monte Carlo method to simulate the surface of the structure. According to the principle of geometric optics, the reflection model of the laser beam on the surface of the structure is derived. The surface of the main amplification system is simulated using this model, and the parameters of the optical path are used to calculate the relationship between surface roughness and residual reflected light reflected into the amplifier. The surface treatment process is applied to our project. By increasing the surface roughness of the structure, the resonant cavity loss is greater than the gain, which provides a basis for suppressing the self-oscillation of the main amplification system of high-power laser devices.
For high-power laser devices using off-axis multi-pass amplification technology, the technology to suppress self-oscillation is of great research value. It is found in engineering practice that the surface of the structure near the aperture of the main amplification system is relatively bright, thus when the amplifier is working, with sufficient gain, a resonant cavity is formed between the bright structural surface and the cavity mirror to generate self-oscillation and ablation. In this paper, this problem of the device is studied by using Monte Carlo method to simulate the surface of the structure. According to the principle of geometric optics, the reflection model of the laser beam on the surface of the structure is derived. The surface of the main amplification system is simulated using this model, and the parameters of the optical path are used to calculate the relationship between surface roughness and residual reflected light reflected into the amplifier. The surface treatment process is applied to our project. By increasing the surface roughness of the structure, the resonant cavity loss is greater than the gain, which provides a basis for suppressing the self-oscillation of the main amplification system of high-power laser devices.
2020,
32: 011021.
doi: 10.11884/HPLPB202032.190269
Abstract:
Reliability design requirements for large and complex equipment pose new challenges to numerical simulation of structural dynamics. In this paper, based on self-developed parallel computing platform PANDA, the modal superposition method is used to calculate the random vibration response under multi-point foundation excitation. The algorithm design and parallel implementation are carried out, and the corresponding solving module is constructed. Taking the six-degree-of-freedom platform structure in the target positioning prototype of Shenguang facility as a numerical example, the modal and random vibration responses of the structure under ground fluctuating load are analyzed with our self-developed progress modules in PANDA platform. The analysis results are compared with the test results and commercial software analysis results. In terms of mode frequency, mode shape and displacement response, the results are consistent, which verifies the correctness of the relevant software and proves the feasibility of PANDA platform in actual engineering structural analysis. The correlative studies have important significance on solving dynamic analysis problems of complex equipments with autonomic software and breaking limitations of commercial finite element software.
Reliability design requirements for large and complex equipment pose new challenges to numerical simulation of structural dynamics. In this paper, based on self-developed parallel computing platform PANDA, the modal superposition method is used to calculate the random vibration response under multi-point foundation excitation. The algorithm design and parallel implementation are carried out, and the corresponding solving module is constructed. Taking the six-degree-of-freedom platform structure in the target positioning prototype of Shenguang facility as a numerical example, the modal and random vibration responses of the structure under ground fluctuating load are analyzed with our self-developed progress modules in PANDA platform. The analysis results are compared with the test results and commercial software analysis results. In terms of mode frequency, mode shape and displacement response, the results are consistent, which verifies the correctness of the relevant software and proves the feasibility of PANDA platform in actual engineering structural analysis. The correlative studies have important significance on solving dynamic analysis problems of complex equipments with autonomic software and breaking limitations of commercial finite element software.
2020,
32: 011022.
doi: 10.11884/HPLPB202032.190146
Abstract:
Efficient broadband harmonic conversion has important application value in high power laser. However, it is difficult to achieve broad bandwidth and high efficiency at the same time in the traditional second harmonic generation (SHG). This paper proposes a novel broadband SHG scheme, which uses the space-time coupling effect to transform the temporally chirped pulse into a spatially chirped one, and then several spliced crystals are used to achieve efficient broadband frequency conversion. Simulation results show that for the spliced KDP crystal, the conversion efficiency of the fundamental harmonic reaches about 60%, for pulse bandwidth of 30 nm and central wavelength of 1 053 nm. Moreover, the frequency doubled light is still linear and broadband, and can be compressed as the fundamental pulse.
Efficient broadband harmonic conversion has important application value in high power laser. However, it is difficult to achieve broad bandwidth and high efficiency at the same time in the traditional second harmonic generation (SHG). This paper proposes a novel broadband SHG scheme, which uses the space-time coupling effect to transform the temporally chirped pulse into a spatially chirped one, and then several spliced crystals are used to achieve efficient broadband frequency conversion. Simulation results show that for the spliced KDP crystal, the conversion efficiency of the fundamental harmonic reaches about 60%, for pulse bandwidth of 30 nm and central wavelength of 1 053 nm. Moreover, the frequency doubled light is still linear and broadband, and can be compressed as the fundamental pulse.
