The 1064 nm laser damage experimental system was established to study the spatiotemporal evolution of plasma generated by K9 window, fused silica, CaF2 and MgF2. In the experiment, the ICCD camera was used to capture the plasma morphology at a fixed delay time, while a fiber optic spectrometer was used to collect spectral information of spontaneous emission during the plasma evolution process. The evolution process of plasma generated by K9 window and fused silica was relatively similar, and the evolution process of plasma generated by CaF2 and MgF2 was relatively similar too. The transient plasma morphology of different optical windows induced by 1064 nm laser were diverse, indicating that the evolution process of laser plasma had become a unique feature of optical windows. The lifetime of plasma of K9 window, fused silica, CaF2 and MgF2 was about 2000 ns, 500 ns, 500 ns and 500 ns induced by 1064 nm laser. Due to the damage thresholds of different optical windows, the time from plasma generation to disappearance was also different. The results of spectral analysis indicated that the plasma spectrum had a direct correlation with the elemental composition of the optical window itself and comparing the spectra of the same optical window under different delay conditions, it could be seen that the delay time of the maximum spectral peak intensity was correlated with the plasma lifetime of optical windows.
Vanadium dioxide film can be used to anti-laser interference infrared detector. If the laser energy is strong enough, the film may also be damaged under laser irradiation. VO2 thin films were prepared on sapphire substrates by molecular beam epitaxy. The laser damage threshold test of VO2 film was designed. VO2 film was irradiated with 1064 nm laser, and the damage characteristics of the film were observed by metallographic microscope. The damage threshold of the film was determined according to the damage morphology. The experimental equipment of laser pretreatment to enhance the film damage threshold was set up, and the laser energy of 20%-90% of the film damage threshold was used to pretreat the film. It is found that there is an optimal pretreatment energy for raising the damage threshold of vanadium dioxide films by laser pretreatment, and the optimal pretreatment energy is 60% of the damage threshold energy. The damage threshold of vanadium dioxide films pretreated with this energy was increased by about 31%.
The deep ultraviolet optical thin films play an important role in excimer lasers, deep ultraviolet lithography machine and other laser systems. In this paper, the experiment on damage in HfO2/ SiO2 high reflective film irradiated by 248nm ultraviolet excimer laser was carried out. And the high reflection film is coated with a layer of SiO2 as a protective film. The damage morphology and depth of the samples were observed and analyzed by means of DIC microscope and surface profiler system. In this experiment, the laser-induced damage threshold of HfO2/ SiO2 high reflective film coated with SiO2 protective film was calculated by zero damage probability. Based on the surface characteristics of the damage points, we established the model to analyze the damage mechanism of the high reflectance film by using Finite Element Method(FEM). The experimental results show that the damage threshold of 248nm excimer laser to the highly reflective film is 3.086J/cm2. When the incident laser energy is 3.33J/cm2, stress damage appears on the surface of the highly reflective film. With the increase of laser energy, the high reflective film will appear melting damage and corrugated damage.
The study of the influence of the changes of laser parameters on the temperature field distribution of PbS detector irradiated under 2.79μm mid-infrared laser has important reference value. In this paper, the theoretical simulation of a typical PbS detector irradiated by a 2.79μm mid-infrared laser is carried out by using the Finite Element Analysis method (FEA). The maximum temperature of PbS detector irradiated by 2.79μm mid-infrared laser with different laser parameters is investigated. The maximum temperature on the photosensitive surface of the PbS detector under different conditions is obtained by adjusting the spot radius, pulse width, and repetition frequency of the simulated pulsed laser. The effects of the changes of spot size, repetition frequency and pulse width on the maximum temperature of the photosensitive surface are investigated. The simulation results show that under the same energy density irradiation condition, the maximum temperature of the photosensitive surface decreases with the increase of the spot radius and pulse width. Under the condition of the same spot radius and pulse width, the higher repetition frequency can make the maximum temperature of photosensitive surface reach a higher temperature. This work gives the law of the temperature changes of the photosensitive surface caused by changing the laser parameters, which is helpful to improve the damage resistance of PbS detector to high power 2.79μm mid-infrared laser step by step.
In this paper, the damage characteristics of MgF2 window material were investigated by building a 193 nm UV excimer laser damage experimental system under different laser fluences of 193 nm excimer laser. The damage morphology was also observed by differential phase contrast microscopy (DIC). The damage mechanism of 193 nm excimer laser irradiated MgF2 window material was investigated. Finite element simulation experiments were also conducted for the defective MgF2 window material. The distribution of temperature and stress fields in the 193 nm UV laser irradiated MgF2 window material was numerically analyzed using the finite element method. The results show that when the laser irradiates the MgF2 window material, the damage threshold of the rear surface of the window material is 2.523 J/cm2 and the damage threshold of the incident surface is 9.74 J/cm2, that is, the rear surface is damaged before the incident surface. At the same time, the rear surface damage profile increased catastrophically with the growth of irradiated laser energy, while the incident surface damage profile increased linearly with the growth of irradiated laser energy. The main factor causing the damage to the window material is the damage caused by the defects contained in it, which causes stress damage to the window material during laser irradiation.
Polyimide (PI) irradiated by pulsed CO2 laser was simulated by finite element method. The finite element model of PI damaged by pulsed CO2 laser was established. We analyzed the temperature and stress characteristics of PI sample under laser irradiation. The effects of laser pulse width and laser spot radius on the damage effect were discussed. The simulation results show that when the stress does not reach the tensile limit,PI will have melt damage,and the body damage is prior to the surface damage. Under the same laser energy irradiation,the thermal stress produced by short pulsed laser is larger than that produced by long pulsed laser,and the effect of thermal stress damage is better. The peak value of stress decreases with the increase of laser spot radius. The larger spot radius is,the worse damage effect is. The occurrence time of peak stress is independent of spot radius.
The damage characteristics of the indium-tin-oxide (ITO) layer and the polyimide (PI) layer, which are two constituent components of a LCD, induced by a high-peak-power laser and a high-average-power laser are investigated. The PI alignment layer is pinned on the ITO film to imitate the structure of the LCD as much as possible in our study. Under the irradiation of the high-peak-power laser, the damage process of the PI/ITO/SUB sample involves thermally induced plastic deformation, followed by cooling when the irradiation fluence is near the LIDT, and rupture when the irradiation fluence is higher. High-average-power laser irradiation results in damaged morphologies of the bulge for the PI/ITO/SUB sample. The temperature distributions induced by the pulsed laser and the high-repetition-rate laser are investigated. The damage is attributed to the intrinsic heat absorption of the ITO films. Under the irritation of the high-peak-power laser, the temperature rises rapidly to a high degree at very short time because of the instant strong absorption in ITO layer, and resulted in vaporization of ITO layer consequently. Subsequently, the vaporized ITO breaks through the surface PI and develops the visible damage. However, under the irritation of high-average-power laser, ITO layer absorbs laser energy, resulting in a slow temperature rise and a small temperature gradient.
Quasi-CW laser damage process of indium tin oxide (ITO) thin film was investigated. The ITO film with thickness of 300 nm was deposited on fused silica substrate by magnetron sputtering. Experiments were conducted on quasi-CW laser with wavelength of 1064 nm, and the test was executed in single shot test with radiation time of 60 s. The damage morphologies were observed via optical microscope and scanning electron microscope (SEM). The apparent damage started with change in color which the morphologies were visible to the naked eyes. With the power density higher than the laser induced damage threshold (LIDT), there were cracks in the center of the damage site. The temperature distribution of the ITO thin film was investigated based on the heat equation.
It has very important application value to investigate the damage mechanism of CaF2 windows irradiated by ultraviolet excimer laser. As significant optical materials, CaF2 windows have been widely used in the ultraviolet photoelectrical field. Because the ultraviolet excimer laser presents favorable characteristics such as short wavelength and high photon energy, the high power excimer lasers are expected to be widely applied in precision laser machining and military field. In this paper, the experiment on damage in CaF2 windows irradiated by 248nm ultraviolet excimer laser was carried out. The damage characteristics of irradiated spots under different experiment conditions were detected by optical microscope. The laser induced damage thresholds of CaF2 windows were calculated by the zero damage probability through linear fitting. The damage mechanism of CaF2 windows were discussed based on the surface characteristics of damage spots. The experimental results indicated that the damage thresholds of zero probability for the 248nm excimer laser to CaF2 windows were 5.6J/cm2 of the incident surface, and 1.1J/cm2 of the exit surface respectively. When CaF2 windows was irradiated by 248nm excimer laser, its damage first occurred to its exit surface, the damage threshold of exit surface was smaller than that of incident surface. As the laser fluence increased gradually, the damage of exit surface was shown to grow exponential and its degree was significantly higher than that of incident surface. This work is helpful to further improve damage resistance of CaF2 windows in high power laser facility. It can provide the necessary references for selection of ultraviolet optical materials and optimization of application.
The damage of a nanosecond pulse laser on ultraviolet(UV) image intensifier was studied. A laser pulsed with a wavelength of 266nm and pulse width of 25ns was used to radiate an UV imager intensifier. The laser induced damage threshold(LIDT) of the internal components of the UV imager intensifier was measured, and the LIDTs of the optical windows, the microchannel plate and the ultraviolet photocathodes are 1.8mJ / cm2 , 3.3mJ / cm2 and 17.6 mJ / cm2, respectively. It is shown that as the incident laser energy increases, the order of damage of the components inside the image intensifier is: photocathode, microchannel plate and optical window.
The 1064nm fundamental wave (FW) and the 532nm second harmonic wave (SHW) of Nd:YAG laser have been widely applied in many fields. In some military applications requiring interference in both visible and near-infrared spectrum range, the de-identification interference technology based on the dual wavelength composite output of FW and SHW offers an effective way of making the device or equipment miniaturized and low cost. In this paper, the application of 1064nm and 532nm dual-wavelength composite output technology in military electro-optical countermeasure is studied. A certain resonator configuration that can achieve composite laser output with high power, high beam quality and high repetition rate is proposed. Considering the thermal lens effect, the stability of this certain resonator is analyzed based on the theory of cavity transfer matrix. It shows that with the increase of thermal effect, the intracavity fundamental mode volume decreased, resulting the peak fluctuation of cavity stability parameter. To explore the impact the resonator parameters does to characteristics and output ratio of composite laser, the solid-state laser’s dual-wavelength composite output models in both continuous and pulsed condition are established by theory of steady state equation and rate equation. Throughout theoretical simulation and analysis, the optimal KTP length and best FW transmissivity are obtained. The experiment is then carried out to verify the correctness of theoretical calculation result.
The 248 nm excimer laser etching characteristic of alumina ceramic and sapphire had been studied using different laser fluence and different number of pulses. And the interaction mechanism of 248 nm excimer laser with alumina ceramic and sapphire had been analyzed. The results showed that when the laser fluence was less than 8 J/cm2, the etching depth of alumina ceramic and sapphire were increased with the increase of laser fluence and number of pulses. At the high number pulses and high-energy, the surface of the sapphire had no obvious melting phenomenon, and the alumina ceramic appeared obvious melting phenomenon. The interaction mechanism of excimer laser with alumina ceramics and sapphire was mainly two-photon absorption. But because of the existence of impurities and defects, the coupling between the laser radiation and ceramic and sapphire was strong, and the thermal evaporation mechanism was also obvious.
The damages of TEA-CO2 laser to HgCdTe imaging sensor are researched experimentally and theoretically. The shadows, cracks and dark line are observed. There is a gap between photosensitive layer and CdZnTe which decreases light transmittance, so that the shadows occur. It shows that the crack damages begin from photosensitive layer. The sensor is irradiated by pulse laser, the absorptivity of photosensitive layer is strong, sharp temperatures fluctuations inside the sensor, leading to stress. With the stress increased, the cracks are observed on the surface of the detector. Cracked the surface of the substrate, and effective transmission reduced, which caused gray pixel response decline. The dark line in image occurs several times because Hg atoms separate out from the detector and gather together at the Si-COMS which makes a short circuit between silicon substrate and signal choice line. The volatility of Hg makes the short circuit is unstable, resulting in the dark line repeated in the output image, but the short circuit occurs by chance.
The theoretical model of K9 glass irradiated by a 248-nm KrF excimer laser was established, and a numerical simulation was performed to calculate temperature and thermal stress fields in the K9 glass sample using the finite element method. The laser-induced damage thresholds were defined and calculated, and the effect of repetition frequency and the number of pulses on the damage threshold were also studied. Furthermore, the experiment research was carried out to confirm the numerical simulation. The damage threshold and damage morphology were analyzed by means of a metallurgical microscope and scanning electron microscopy. The simulation and experimental results indicated that the damage mechanism of K9 glass irradiated by a KrF excimer laser was melting damage and stress damage, and the stress damage first appeared inside the K9 glass sample. The tensile stress damage threshold, the compressive stress damage threshold, and the melting damage threshold were 0.64, 0.76, and 1.05 J/cm2, respectively. The damage threshold decreased with increasing repetition frequency and number of laser pulses. The experimental results indicated that the damage threshold of K9 glass was 2.8 J/cm2.
The optical component of photoelectric system was easy to be damaged by irradiation of high power pulse laser, so the effect of high power pulse laser irradiation on K9 glass was researched. A thermodynamic model of K9 glass irradiated by ultraviolet pulse laser was established using the finite element software ANSYS. The article analyzed some key problems in simulation process of ultraviolet pulse laser damage of K9 glass based on ANSYS from the finite element models foundation, meshing, loading of pulse laser, setting initial conditions and boundary conditions and setting the thermal physical parameters of material. The finite element method (FEM) model was established and a numerical analysis was performed to calculate temperature field in K9 glass irradiated by ultraviolet pulse laser. The simulation results showed that the temperature of irradiation area exceeded the melting point of K9 glass, while the incident laser energy was low. The thermal damage dominated in the damage mechanism of K9 glass, the melting phenomenon should be much more distinct.
Excimer laser with nanosecond pulse duration can induce low thermal budget processing and heating confinement near the surface region, which make excimer laser annealing process suitable for low-temperature growth of oxide films. This work presented 248 nm KrF excimer laser irradiation processes of ZnO films prepared by a DC magnetron sputtering method. The influence of the laser energy densities on the structural, morphology, optical and electrical characteristics of ZnO films were investigated. The results presented that the crystallinity of ZnO films could be raised obviously by the excimer laser annealing process. The film under laser irradiation with 137 mJ/cm2 outputs showed the lowest sheet resistance of 10 kΩ/□ and high visible transmittance (~77.4%). This study indicated that excimer laser annealing is a useful method for the performance improvement of oxide films.
The damage of K9 glass under 248nm ultraviolet pulsed laser irradiation was studied. The laser pulse energy was kept within the range of 60mJ to 160mJ, and the repetition rate was adjusted within the range of 1Hz to 40Hz. The damage morphologies of single-pulse and multi-pulse laser irradiation were characterized by optical microscope, and the damage mechanism was discussed. The experimental results indicated that the damage of K9 glass irradiated by 248nm ultraviolet laser mainly followed the thermal-mechanical coupling mechanism and the damage threshold of K9 glass was 2.8J/cm2. The intensity of damage area increased gradually with the increase of the laser pulse number. It was shown that accumulation effect of laser induced damage to K9 glass was obvious.
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