To further study the saturation characteristics of photodetectors irradiated using ultrashort pulse lasers, silicon-based PN-type photodiodes were used as experimental devices to measure the transient response time of picosecond laser irradiated devices with different laser energy densities. The experimental results show that the transient response signal of the device is nonlinearly saturated when the picosecond laser energy density reaches 97 nJ/cm². Furthermore, we analyze the signal’s full widths at half maximum and signal’s bottom widths of the signal characteristic quantity after the device saturation. The absolute and relative increases are obtained as 154 μs, 157.00% and 157 μs, 47.87%, respectively. Observe that as the laser energy density increases, the response time gradually increases. The time extension of the signal indicates the occurrence of the transient response degeneration of the device. Through the analysis of laser injection carriers, a large number of photogenerated carriers are generated after the laser irradiation, satisfying large injection conditions of semiconductors. This leads to bipolar mobility approaching zero during the initial carrier bipolar transport process. The initial speed of the corresponding signal falling edge attenuates, leading to the degrading response signal of the device.