Study on Characteristics of the Light-Initiated High Explosive-Based Pulse Laser Initiation

The silver acetylene silver nitrate loading technology of the light initiated high explosive, as one of important means to simulate the structural response of powerful pulsed X-ray, adopts the pulse laser initiation. It has advantages of improvement of practical control, heterogenous loading realization and simultaneous loading timeliness. In this paper, the physical and mathematical models of hot spot initiation and photochemical initiation of energetic materials under the action of laser are firstly established, and then the laser initiation mechanism of the light initiated high explosive is specifically analyzed, and the laser initiation experiment is conducted based on the optical adsorption property of the light initiated high explosive. From this study, the laser initiation thresholds of 193 nm, 266 nm, 532 nm, 1064 nm wavelengths are given, and they are 5.07 mJ/mm2, 6.77 mJ/mm2, 7.21 mJ/mm2 and 10.61 mJ/mm2, respectively, and the complete detonation process is verified by detonation velocity. This work technically supports the study of pulse laser initiation process, mechanism and explosion loading rule as well as the loading technology of the light initiated high explosive to simulate the structural response of X ray.


Introduction
The light-initiated high explosive (LIHE) is a practicable experimental simulation technology used to simulate the structural response of a powerful pulsed X-ray [1], which can effectively solve problems, such as the complex heterogeneity of the shell, small specific impulse simulation, and simultaneous loading of large planar array, and it is also the only simulation technology that can simulate the material response caused by X-ray and structural response simultaneously.
The light-initiated high explosive (LIHE) facility, at this time, is used primarily to investigate the structural response of complex test items, such as re-entry bodies/vehicles to shock-producing events [2,3]. Tests at a LIHE facility are high-fidelity tests, meaning that the test loading is delivered in the proper time frame, and applied over the entire test surface at the same time [4]. During a hostile encounter-such as a nuclear weapon detonated in space near a re-entry vehicle-hot, warm, and cold X-rays are produced. When cold X-rays deposit themselves in a thin layer on the asset's surface, that material heats up nearly instantaneously and vaporizes, sending a shock wave into the structure. This can cause many types of problems with external materials and internal components. By knowing the effects of these events on systems and components, designers can take action to counter them [5][6][7][8][9][10]. Light-initiated high explosive (LIHE) is the only available and highly realistic experimental technique to simulate the structural response of an intense pulse X-ray, which can solve the problems of complex shell anisotropy, simulation of small model established by Sun et al. [16] is often used, which is shown in Figure 1, and it is a typical thermal mechanical theory, based on the heat conduction. For the chemical reaction term, the typical laser initiation model is shown as follows: where ρ is the density of agent; C is the thermal capacity of agent 1; K is the heat conductivity coefficient of agent; I 0 is the laser intensity; Q is the chemical reaction heat of agent; A is the frequency factor; and E is the activation energy of agent.
Materials 2022, 15, x FOR PEER REVIEW 3 of 14 laser initiation model established by Sun et al. [16] is often used, which is shown in Figure  1, and it is a typical thermal mechanical theory, based on the heat conduction. For the chemical reaction term, the typical laser initiation model is shown as follows: where ρ is the density of agent; C is the thermal capacity of agent 1; K is the heat conductivity coefficient of agent; I0 is the laser intensity; Q is the chemical reaction heat of agent; A is the frequency factor; and E is the activation energy of agent.

Thermal Mechanism Process Analysis
To study the ignition characteristics of LIHE under the action of laser, the laser should first be expressed in a form of heat, and then conducted to LIHE. The distribution rule equation of internal temperature of a heat-conducting material is a differential equation of heat conduction. The expression under a rectangular coordinate system is shown as follows: The heat conduction equation without internal heat source meets Laplace's equation: For uniform LIHE, it is assumed that its chemical and physical properties remain unchanged during temperature rising, and it is known from the heat conduction theory that the energy conservation equation of ignition heat is shown as follows: is chemical reaction heat; and j = 0, 1 represents 1D and 2D models, respectively. The boundary condition meets category II boundary conditions, and it is expressed as follows: where ρ is the density of LIHE (kg/m 3 ); c is the specific heat of LIHE (J/kg·K); λ is the heat conductivity coefficient (W/m·K); Q is the chemical reaction heat of LIHE (J/kg); A is the frequency factor (S −1 ); R is the universal gas constant (J/mol·K); I is the incoming laser intensity (W/cm 2 ); f is the reflectivity of agent; α is the absorption coefficient of the sample to the laser (1/m); b is the convective heat transfer coefficient of sample and environment; Ea is the activation energy of agent (J/mol); and a0 is the thickness of the agent. It is assumed that the laser distribution is uniform, so

Thermal Mechanism Process Analysis
To study the ignition characteristics of LIHE under the action of laser, the laser should first be expressed in a form of heat, and then conducted to LIHE. The distribution rule equation of internal temperature of a heat-conducting material is a differential equation of heat conduction. The expression under a rectangular coordinate system is shown as follows: The heat conduction equation without internal heat source meets Laplace's equation: For uniform LIHE, it is assumed that its chemical and physical properties remain unchanged during temperature rising, and it is known from the heat conduction theory that the energy conservation equation of ignition heat is shown as follows: where (1 − f )αI exp(−αx) is laser energy; ρQA exp(− E a RT ) is chemical reaction heat; and j = 0, 1 represents 1D and 2D models, respectively. The boundary condition meets category II boundary conditions, and it is expressed as follows: where ρ is the density of LIHE (kg/m 3 ); c is the specific heat of LIHE (J/kg·K); λ is the heat conductivity coefficient (W/m·K); Q is the chemical reaction heat of LIHE (J/kg); A is the frequency factor (S −1 ); R is the universal gas constant (J/mol·K); I is the incoming laser intensity (W/cm 2 ); f is the reflectivity of agent; α is the absorption coefficient of the sample to the laser (1/m); b is the convective heat transfer coefficient of sample and environment; E a is the activation energy of agent (J/mol); and a 0 is the thickness of the agent. It is assumed that the laser distribution is uniform, so where H(t) is Heaviside function, which means that H(t) = 1, t > 0; H(t) = 0, t ≤ 0; and ω r is the laser beam radius. With Laplace conversion and convolution theorem application, the analytical solution of energy conservation equation is shown as follows where η is the photothermal conversion coefficient and erfc is the error function; then The expression of T on the surface of energetic material (x = 0) is shown as follows: The ignition energy of energetic material is shown as follows: With the laser ignition process based on thermal mechanism analyzed, the physical model and the mathematical model are established. Upon the calculation of the heat conduction equation, established by boundary conditions, the relations between the critical energy of the ignition and the initial parameter of energetic material, and the relations between the material surface and the time, can be obtained. It can be seen from Equation (9) that the rise in surface temperature of the energetic material is directly proportional to the laser power, and the energy of the laser ignition is inversely proportional to the power. From the results, it is known that the increase in laser power positively affects the laser ignition process, based on the thermal mechanism. Moreover, as the energy output of the laser remains unchanged, it is of significant importance to reduce the loss of laser during transmission, for the improvement of ignition performance.

Photochemical Mechanism Process Analysis
The photochemical effect of LIHE is analyzed based on its optical absorption property. A SASN molecule absorbs the laser photon with a specific frequency and then dissociates, and the high-activity fast particles from the dissociation lead to a further chemical chain reaction, so that the ignition is caused; this is a photochemical ignition. Under the action of a specific frequency laser, the material molecule directly photolyzes, and causes the chain reaction in the material. The explosion reaction of Ag 2 C 2 ·AgNO 3 is shown as follows: Ag 2 C 2 ·AgNO 3 →3Ag + CO 2 + CO + N 2 (12) For example, when SASN is radiated by a laser with a wavelength 190 nm, the reaction is shown as follows: Ag 2 C 2 + hv (190 nm)→2Ag + 2C 2C + 2AgNO 3 →2CO + 2Ag + 2O 2 + N 2 (14) 2CO The final result when a wavelength is 190 nm is: Ag 2 C 2 ·AgNO 3 + hv→3Ag + CO 2 + CO + N 2 (16) The above reaction process is caused by the photochemistry, and contains the chain mechanism. The dissociation caused when a SASN substance molecule absorbs several photons simultaneously or successively is called the multiple photon dissociation. The transition probability in the n photon transition process is shown as follows Wn = ∑n n 0 n + O(n 0 n ) (17) where ∑n (unit cm 2n s n−1 ) is n step transition section, n 0 is the photon stream density, and Wn is n photon transition probability. Without the intermediate state resonance, item 2 in the Equation (8) can be ignored, and then: Wn = ∑n n 0 n = ∑n (I 0 /hv) n (18) The above equation means that the transition probability Wn of n photon absorption is directly proportional to the nth power of the laser intensity I 0 . Usually, the single-photon absorption section ∑ 1 ranges from 10 −16 to 10 −22 cm 2 , while the double-photon absorption section ∑ 2 ranges from 10 −48 to 10 −57 cm 4 s, and the ∑n value greatly decreases with the increase in n. Therefore, the multiple-photon phenomenon is rarely observed under normal light source conditions. As the laser power density I 0 in the Equation (19) is large enough (I 0 ≥ 10 6 W/cm 2 ), there is an obvious multi-photon absorption (MPA) phenomenon, so that the observable multi-photon dissociation (MPD) effect will occur. Two conditions need to be met for SASN initiation under the photochemical action of laser: The laser wavelength is strictly matched with the absorption wavelength of SASN, and then the energetic material can be photolyzed, due to resonance absorption to the laser; 2.
The laser energy of irradiation SASN is not too small.

Pulse Laser Initiation Platform
The experimental system of laser initiation platform consists of a laser, light path, SASN sample, energy meter, spectrometer, photoelectric probe, high-speed camera, and experimental protector. The schematic diagram of system composition and real platform are shown in Figures 2 and 3. The Photocell is ET-2030 of ETL, the spectrometer is AvaSpec-ULS2048, and the spectral measurements range is 200 nm to 1400 nm. The pressure is CA-1135 of Dynasen, the high-speed camera is V2512 of Phantom. mechanism. The dissociation caused when a SASN substance molec photons simultaneously or successively is called the multiple photo transition probability in the n photon transition process is shown as f where ∑n (unit cm 2n s n−1 ) is n step transition section, n0 is the photon Wn is n photon transition probability. Without the intermediate state the Equation (8) can be ignored, and then: The above equation means that the transition probability Wn of n is directly proportional to the nth power of the laser intensity I0. Usuall absorption section ∑1 ranges from 10 −16 to 10 −22 cm 2 , while the double section ∑2 ranges from 10 −48 to 10 −57 cm 4 s, and the ∑n value greatly increase in n. Therefore, the multiple-photon phenomenon is rare normal light source conditions. As the laser power density I0 in the E enough (I0 ≥ 10 6 W/cm 2 ), there is an obvious multi-photon absorption (M so that the observable multi-photon dissociation (MPD) effect will oc need to be met for SASN initiation under the photochemical action of 1. The laser wavelength is strictly matched with the absorption w and then the energetic material can be photolyzed, due to reson the laser; 2. The laser energy of irradiation SASN is not too small.

Pulse Laser Initiation Platform
The experimental system of laser initiation platform consists of SASN sample, energy meter, spectrometer, photoelectric probe, high experimental protector. The schematic diagram of system compositio are shown in Figures 2 and 3. The Photocell is ET-2030 of ETL, AvaSpec-ULS2048, and the spectral measurements range is 200 nm pressure is CA-1135 of Dynasen, the high-speed camera is V2512 of P   Two laser initiation platforms were set up based on different experimental requirements. The laser included a ArF excimer laser and Q-smat450 pulsed laser. Table  1 shows the basic parameters of the laser. The ArF excimer laser had a main wavelength 193 nm ultraviolet light and obvious attenuation in the air, and the test results of laser attenuation in the air are shown in Table 2. It can be seen that LIHE is not conducive to practical application, although it has a high-absorption for ultraviolet light. The 2D and 3D representations of the distributions of energy of the Qsmart-450 laser with different wavelengths are shown in Figure 4. From the figure, it is seen that the energy platform of laser obviously facilitates the synchronous loading of laser initiation LIHE within the beam spot range. Two laser initiation platforms were set up based on different experimental requirements. The laser included a ArF excimer laser and Q-smat450 pulsed laser. Table 1 shows the basic parameters of the laser. The ArF excimer laser had a main wavelength 193 nm ultraviolet light and obvious attenuation in the air, and the test results of laser attenuation in the air are shown in Table 2. It can be seen that LIHE is not conducive to practical application, although it has a high-absorption for ultraviolet light. The 2D and 3D representations of the distributions of energy of the Qsmart-450 laser with different wavelengths are shown in Figure 4. From the figure, it is seen that the energy platform of laser obviously facilitates the synchronous loading of laser initiation LIHE within the beam spot range.

Properties of Silver Acetylene-Silver Nitrate of LIHE
The silver acetylene-silver nitrate is the complex of silver acetylene and silver nitrate, with a molecular formula Ag2C2·AgNO3, and is insoluble in water, ethanol, diethyl ether, and acetone. In the conventional synthesis and preparation method, the acetylene gas is injected into the aqueous solution of silver nitrate, and the white flocculent precipitate

Properties of Silver Acetylene-Silver Nitrate of LIHE
The silver acetylene-silver nitrate is the complex of silver acetylene and silver nitrate, with a molecular formula Ag 2 C 2 ·AgNO 3 , and is insoluble in water, ethanol, diethyl ether, and acetone. In the conventional synthesis and preparation method, the acetylene gas is injected into the aqueous solution of silver nitrate, and the white flocculent precipitate generated is Ag 2 C 2 ·AgNO 3 .
Silver acetylene-silver nitrate is an unstable substance, which decomposes under a strong light exposure and generate a huge amount of gas, as well as gives out heat. The decomposition reaction equation is shown as follows: The surface topography of the sample under different resolutions is characterized with the scanning electron microscope (SEM), as shown in Figure 5. The sample is formed by spherical nanoparticles with a diameter of 90 nm, and there is neat and orderly crystal formation, a smooth surface, and uniform size distribution; all these properties facilitate the synchronous initiation and loading.

Properties of Silver Acetylene-Silver Nitrate of LIHE
The silver acetylene-silver nitrate is the complex of silver acetylene and silver nitrate, with a molecular formula Ag2C2·AgNO3, and is insoluble in water, ethanol, diethyl ether, and acetone. In the conventional synthesis and preparation method, the acetylene gas is injected into the aqueous solution of silver nitrate, and the white flocculent precipitate generated is Ag2C2·AgNO3.
Silver acetylene-silver nitrate is an unstable substance, which decomposes under a strong light exposure and generate a huge amount of gas, as well as gives out heat. The decomposition reaction equation is shown as follows: The surface topography of the sample under different resolutions is characterized with the scanning electron microscope (SEM), as shown in Figure 5. The sample is formed by spherical nanoparticles with a diameter of 90 nm, and there is neat and orderly crystal formation, a smooth surface, and uniform size distribution; all these properties facilitate the synchronous initiation and loading. The X-ray diffraction (XRD) was used to characterize the test (scanning range: 5~90°), and the test results are shown in Figure 6. It shows that the position of sample diffraction peak is basically consistent with that of XRD diffraction peak of the silver acetylene-silver nitrate, and this verifies the composition of LIHE. The X-ray diffraction (XRD) was used to characterize the test (scanning range: 5~90 • ), and the test results are shown in Figure 6. It shows that the position of sample diffraction peak is basically consistent with that of XRD diffraction peak of the silver acetylene-silver nitrate, and this verifies the composition of LIHE. The sample was tested in infrared by a Fourier infrared spectr number tested ranged from 4000 to 500 cm −1 . The test results are s The sample was tested in infrared by a Fourier infrared spectrometer, and the wave number tested ranged from 4000 to 500 cm −1 . The test results are shown in Figure 7. The functional group region is 3700~1333, while the fingerprint region is 1333~650, and the infrared spectrograms of the sample include two strong absorption peaks of CO 2 in the atmosphere. They are near 2349 cm −1 and 667 cm −1 , and meet the infrared spectral characteristics of the acetylene bond (-C≡C-) in the silver acetylene. For samples, the absorption peak appears at 1385 cm −1 or 840 cm −1 , and they correspond to the antisymmetric stretching and vibration peaks of silver nitrate in the silver acetylene-silver nitrate.
functional group region is 3700~1333, while the fingerp infrared spectrograms of the sample include two strong atmosphere. They are near 2349 cm −1 and 667 cm −1 , characteristics of the acetylene bond (-C≡C-) in the si absorption peak appears at 1385 cm −1 or 840 cm −1 antisymmetric stretching and vibration peaks of silver ni nitrate. The SASN full-band absorption spectrum curve is s has a good absorption of ultraviolet light, with a wavele nm, and the SASN absorption reduces quickly between absorption is not obvious if the wavelength is greater th  The SASN full-band absorption spectrum curve is shown in Figure 8. It is seen that it has a good absorption of ultraviolet light, with a wavelength ranging from 190 nm to 300 nm, and the SASN absorption reduces quickly between 300~450 nm, while the SASN absorption is not obvious if the wavelength is greater than 450 nm. number tested ranged from 4000 to 500 cm −1 . The test results are functional group region is 3700~1333, while the fingerprint regi infrared spectrograms of the sample include two strong absorp atmosphere. They are near 2349 cm −1 and 667 cm −1 , and me characteristics of the acetylene bond (-C≡C-) in the silver acet absorption peak appears at 1385 cm −1 or 840 cm −1 , and th antisymmetric stretching and vibration peaks of silver nitrate in th nitrate. The SASN full-band absorption spectrum curve is shown in has a good absorption of ultraviolet light, with a wavelength ran nm, and the SASN absorption reduces quickly between 300 nm~ absorption is not obvious if the wavelength is greater than 450 nm

Experimental Study on Laser Initiation
LIHE specimen is shown in Figure 9, and the specimen p Table 3. SASN was dripped in the center of the aluminum plat probe was placed in the center to measure the pressure an surface density of SASN was 10-70mg/cm 2

Experimental Study on Laser Initiation
LIHE specimen is shown in Figure 9, and the specimen parameters are shown in Table 3. SASN was dripped in the center of the aluminum plate. A Dynasen pressure probe was placed in the center to measure the pressure and time of arrival. The surface density of SASN was 10-70 mg/cm 2    Table 4 shows the experimental parameters of initiation o Figure 10 shows the experimental thresholds of laser initiation S    Table 4 shows the experimental parameters of initiation of different lasers, while Figure 10 shows the experimental thresholds of laser initiation SASN.  From the experimental results, it is seen that SASN is detonated reliably unde different wavelengths of pulsed laser, and the complete detonation is realized only when the energy density is greater than 5.07 mJ/mm 2 at 193 nm, 6.77 mJ/mm 2 at 266 nm, 7.21 mJ/mm 2 at 532 nm, and 10.61 mJ/mm 2 at 1064 nm. This also verifies that SASN ligh absorption reduces with the wavelength (see Figure 10). However, the complete detonation is realized only when the energy density is greater than 29.04 mJ/mm 2 at 355 nm, and there is a higher initiation threshold at 355 nm than at any other wavelength From the experimental results, it is seen that SASN is detonated reliably under different wavelengths of pulsed laser, and the complete detonation is realized only when the energy density is greater than 5.07 mJ/mm 2 at 193 nm, 6.77 mJ/mm 2 at 266 nm, 7.21 mJ/mm 2 at 532 nm, and 10.61 mJ/mm 2 at 1064 nm. This also verifies that SASN light absorption reduces with the wavelength (see Figure 10). However, the complete detonation is realized only when the energy density is greater than 29.04 mJ/mm 2 at 355 nm, and there is a higher initiation threshold at 355 nm than at any other wavelength, which is inconsistent with the characteristic rule inertia of SASN light absorption. Upon analysis, this might be because of a change in the SASN detonation method. The initiation manner of ultraviolet lasers of 193 nm, 266 nm, and 355 nm is mainly dominated by the photochemical ignition, while that of green light 532 nm is mainly dominated by hot spot ignition. These need to be further verified by the physicochemical microanalysis and process spectrum analysis.

Detonation Velocity Measurement of Laser Initiation
To judge the complete detonation, instead of combustion detonation, of laser initiation SASN, its detonation velocity was measured, and from the results, it is seen that the detonation velocity is above 1.3 km/s, and it is deemed as detonated completely. Table 5 and Figure 11 show the detonation velocity and measurement system and waveform, respectively. ignition. These need to be further verified by the physicochemical microanalysis and process spectrum analysis.

Detonation Velocity Measurement of Laser Initiation
To judge the complete detonation, instead of combustion detonation, of laser initiation SASN, its detonation velocity was measured, and from the results, it is seen that the detonation velocity is above 1.3 km/s, and it is deemed as detonated completely. Table  5 and Figure 11 show the detonation velocity and measurement system and waveform, respectively.  Figure 11. Measurement system and actually measured waveform.

Spectral Analysis of Initiation Process
The radiation spectrum of the detonation process of laser initiation LIHE measured by the fiber optic spectrometer is shown below, and Figure 12 is the radiation spectrum from the explosive explosion stimulated by the ArF laser (193 nm), while Figure 13 is the radiation spectrum from the explosive explosion stimulated by the third harmonic generation of Q-smart laser (355 nm). The measured spectrum mainly includes continuous spectrum and characteristic line spectrum. The continuous spectrum is mainly produced by the high-temperature gray body radiation of the explosion, while the characteristic line spectrum is mainly the radiation spectrum generated by a certain element or molecule in the explosion field, under high-temperature conditions or a chemical reaction. Upon the preliminary judgment, the corresponding elements of the measured spectral line mainly include: Ag, Na, K, etc., and the corresponding wavelengths are located as follows: Ag: 520.9 nm and 546.5 nm; Na: 589 nm; and K: 766.5 nm and 769.3 nm. Moreover, the characteristic radiation spectrum near 499 nm is obtained in some experimental measurements, but the element or molecule corresponding to this spectrum remains unknown. The element content in the experiment does not depend on the spectral intensity, and such intensity only means that this spectrometer has a higher absorption for this element. To calibrate the relation between element content and intensity, this spectrometer needs to be further calibrated in a stricter manner.
From spectral results, all element spectrums in the chemical exothermic reaction of SASN initiation are not obtained, so it is difficult to analyze the SASN exothermic reaction

Spectral Analysis of Initiation Process
The radiation spectrum of the detonation process of laser initiation LIHE measured by the fiber optic spectrometer is shown below, and Figure 12 is the radiation spectrum from the explosive explosion stimulated by the ArF laser (193 nm), while Figure 13 is the radiation spectrum from the explosive explosion stimulated by the third harmonic generation of Q-smart laser (355 nm). The measured spectrum mainly includes continuous spectrum and characteristic line spectrum. The continuous spectrum is mainly produced by the hightemperature gray body radiation of the explosion, while the characteristic line spectrum is mainly the radiation spectrum generated by a certain element or molecule in the explosion field, under high-temperature conditions or a chemical reaction. Upon the preliminary judgment, the corresponding elements of the measured spectral line mainly include: Ag, Na, K, etc., and the corresponding wavelengths are located as follows: Ag: 520.9 nm and 546.5 nm; Na: 589 nm; and K: 766.5 nm and 769.3 nm. Moreover, the characteristic radiation spectrum near 499 nm is obtained in some experimental measurements, but the element or molecule corresponding to this spectrum remains unknown. The element content in the experiment does not depend on the spectral intensity, and such intensity only means that this spectrometer has a higher absorption for this element. To calibrate the relation between element content and intensity, this spectrometer needs to be further calibrated in a stricter manner. process, and this is related to the open experimental environment and complicated gas elements. In future experiments, a closed experimental environment (optical fiber for laser transmission) can be considered, and the inert gases can fill a container.

Conclusions
In this paper, the laser initiation model and the photochemical effect process of SASN were established and analyzed. This was followed by the set-up of experimental platform of low-power laser initiation using SASN, and the power density threshold, detonation velocity, spectrum, and other characteristic parameters of laser initiation SASN under different wavelengths were obtained, which provided a technical reference for a chemical explosion method in simulation of structural response of a powerful pulsed X-ray.
1. With the laser ignition process based on thermal mechanism analyzed, the physical model and mathematical model are established. Upon the calculation of the heat conduction equation, established by boundary conditions, the relations between the critical energy of ignition and the initial parameter of energetic material, and the relations between the material surface and the time, are obtained. The rise in surface temperature of energetic material is directly proportional to the laser power, but the energy of the laser ignition is inversely proportional to the power. From the results, it is known that the increase in laser power positively affects the laser ignition process, based on the thermal mechanism. As the energy output of the laser remains unchanged, reducing the loss of laser during transmission is conducive to the improvement of ignition performance; process, and this is related to the open experimental environment and complicated gas elements. In future experiments, a closed experimental environment (optical fiber for laser transmission) can be considered, and the inert gases can fill a container.

Conclusions
In this paper, the laser initiation model and the photochemical effect process of SASN were established and analyzed. This was followed by the set-up of experimental platform of low-power laser initiation using SASN, and the power density threshold, detonation velocity, spectrum, and other characteristic parameters of laser initiation SASN under different wavelengths were obtained, which provided a technical reference for a chemical explosion method in simulation of structural response of a powerful pulsed X-ray.
1. With the laser ignition process based on thermal mechanism analyzed, the physical model and mathematical model are established. Upon the calculation of the heat conduction equation, established by boundary conditions, the relations between the critical energy of ignition and the initial parameter of energetic material, and the relations between the material surface and the time, are obtained. The rise in surface temperature of energetic material is directly proportional to the laser power, but the energy of the laser ignition is inversely proportional to the power. From the results, it is known that the increase in laser power positively affects the laser ignition process, based on the thermal mechanism. As the energy output of the laser remains unchanged, reducing the loss of laser during transmission is conducive to the improvement of ignition performance; From spectral results, all element spectrums in the chemical exothermic reaction of SASN initiation are not obtained, so it is difficult to analyze the SASN exothermic reaction process, and this is related to the open experimental environment and complicated gas elements. In future experiments, a closed experimental environment (optical fiber for laser transmission) can be considered, and the inert gases can fill a container.

Conclusions
In this paper, the laser initiation model and the photochemical effect process of SASN were established and analyzed. This was followed by the set-up of experimental platform of low-power laser initiation using SASN, and the power density threshold, detonation velocity, spectrum, and other characteristic parameters of laser initiation SASN under different wavelengths were obtained, which provided a technical reference for a chemical explosion method in simulation of structural response of a powerful pulsed X-ray.

1.
With the laser ignition process based on thermal mechanism analyzed, the physical model and mathematical model are established. Upon the calculation of the heat conduction equation, established by boundary conditions, the relations between the critical energy of ignition and the initial parameter of energetic material, and the relations between the material surface and the time, are obtained. The rise in surface temperature of energetic material is directly proportional to the laser power, but the energy of the laser ignition is inversely proportional to the power. From the results, it is known that the increase in laser power positively affects the laser ignition process, based on the thermal mechanism. As the energy output of the laser remains unchanged, reducing the loss of laser during transmission is conducive to the improvement of ignition performance; 2.
The photochemical reaction process is analyzed, based on the optical absorption property of LIHE, and the photochemical initiation conditions are proposed;