Irradiation effect of 2.79 μm mid-infrared laser on CMOS image sensor

  Objective  The CMOS image sensors are widely used in aerospace, security monitoring, industrial control, navigation and guidance, image recognition systems and other fields. Most of researches on laser irradiation effect of CMOS image sensor mainly focus on visible and near infrared bands. With the application of more and more lasers with different wavelengths, there is a great risk of damage to optical systems irradiated by out-of-band lasers, and it is necessary to conduct systematic experimental studies on the interaction between out-of-band lasers and photo detectors. In the photoelectric countermeasure, it is very important to study whether the interference and damage can be effectively caused to the detector when the interference and damage are irradiated by the out-of-band laser, and what its mechanism is. The wavelength of 2.79 μm mid-infrared laser is in the atmospheric window, which has the characteristics of small air scattering and long propagation distance. This band is also the working band of most reconnaissance satellites, surveillance satellites, early warning satellites and other space-based systems. In the future space applications, the high-power 2.79 μm mid-infrared laser has a broad application prospect. Therefore, it is of great reference value in the laser attack and defense field to study the irradiation effect of mid-infrared laser on CMOS image sensor.

  Methods  In the experiment, the CMOS image sensor irradiated by 2.79 μm mid-infrared laser is carried out (Fig.1). The computer is connected to the output signal of CMOS image sensor to observe and record the effect of laser irradiation. In order to study the damage effect of laser irradiation on CMOS image sensor, the experiment is divided into two stages. In the first stage, the laser energy is directly irradiated on the sensor without the sapphire focus lens, and the interference effect of 2.79 μm mid-infrared laser on CMOS image sensor is studied. In the second stage, the sapphire focus lens is placed in the optical path to study the damage effect of 2.79 μm mid-infrared laser on CMOS image sensor. The differential interference contrast (DIC) microscope is used to observe the damage morphology of CMOS sensor samples.

  Results and Discussions  The experimental results of laser interference show that saturation and oversaturation appears on the CMOS image sensor with the increase of laser energy (Fig.3). After stopping laser irradiation for a period of time, CMOS can automatically return to the normal working state. The experimental results show that with the increase of the repetition frequency, CMOS image sensor needs less laser energy and less time to achieve saturation or oversaturation of full screen (Fig.5). The experimental results of laser damage show that the phenomenon of saturation, oversaturation, black screen, green screen and bright line are observed with different laser repetition frequency (Fig.8-9). The damage morphology shows that obvious melting damage occurs in the irradiation area of laser spot, and the high laser energy in the center of beam leads to the ablation and evaporation of a large area of pixel material, and the periphery of the spot area is obviously heated, but no cracks appear (Fig.10). It shows that the damage of 2.79 μm mid-infrared laser on CMOS sensor is mainly due to the thermal melting of materials, and the thermal effect is obvious.

  Conclusions  The experimental results indicate that the CMOS image sensor has good anti-interference and anti-damage ability. The damage thresholds of CMOS image sensor irradiated by 2.79 μm mid-infrared laser at a 10 Hz pulse repetition frequency are 0.44 J/cm² for saturation, 0.97 J/cm² for oversaturation, and 203.71 J/cm² for damage, respectively. It can be seen that the damage threshold of the CMOS image sensor is much higher than its interference threshold. The experimental results show that the damage mechanism of CMOS image sensor is mainly melting damage, and the thermal effect is obvious.