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 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 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 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.