Objective Because of the advantages of small size, fast measurement speed, low consumption and high ranging accuracy, pulsed laser rangefinder is widely used in a wide range of military equipment. Therefore, it is crucial to ensure that it is impossible to obtain the correct target distance information. Jamming methods for laser rangefinder can be divided into two kinds: deception jamming and blinding jamming. When the distance between enemy and us is far away, the blinding jamming has higher requirements on the performance of laser and the accuracy of matching tracking equipment, which will lead to an increase in cost and difficulty. So deception jamming is more used in the interference of rangefinder. And high-repetition rate laser technology is always employed in it. At present, most of research on this technology are theoretical analysis and lack of experimental verification. To fill the gap in this part, the influence of high-repetition rate laser power and frequency on jamming efficiency of pulsed laser rangefinder at a fixed distance has been explored in experiments. Meanwhile, the effective jamming rate of laser with different repetition frequency at different distances has also been researched. These studies have a certain reference value for practical engineering application.
Methods The experimental device is composed of a laser rangefinder, a high-repetition rate laser jammer and a protected target (Fig.3). Because the high repetition rate laser jammers are positioned near the protected target, the distance between them and the protected target can be ignored when long-range jamming is carried out. The distance between target and rangefinder without jamming has been measured first. When the frequency of jamming laser is 150 kHz, this distance is measured at different pump currents. Above tests have been repeated respectively at frequencies of 30 kHz and 50 kHz. Effective jamming rate of laser with different frequencies and distances has also been investigated.
Results and Discussions The output power and effective jamming probability can be obtained by changing the pump current when the frequency of jamming laser is 150 kHz (Tab.2). With the pump current increasing to 11.5 A and above, the effective jamming probability increases to 100%. At this time, the minimum value of ranging results is distributed near the blind area of rangefinder, and the maximum value gradually decreases with the power growing (Fig.5). By fitting the distribution of ranging results, it is found that jamming results follow a normal distribution（Fig.6）. And with the increase of output power, the distribution center gradually approaches to the minimum jamming distance which is 1km. Adjust the repetition frequency of the jamming laser to 50, 30 kHz respectively to repeat the above experiments. The minimum distance is still distributed around the blind area of the rangefinder and doesn’t change with the change of frequency. But the maximum value decreases with the increase of frequency (Fig.7 & Fig.8). The distribution of jamming ranging results still follows normal distribution, and the distribution center also tends to the minimum jamming distance which corresponds to laser frequency（Fig.9）. When the pump current is 12 A, the frequency of laser is changed to explore the effective jamming probability at different jamming distances. The higher repetition frequency of jamming laser is, the minimum jamming distance will be shorter and the effective jamming range will be larger (Tab.3).
Conclusions Combining theoretical analysis and field test, the effective jamming probability is taken as the criterion of efficiency evaluation, and a method to judge whether high-repetition rate laser jamming interferes effectively with pulsed laser rangefinder is proposed. The influence rules of the power and repetition frequency of high-repetition rate laser on distance measurement of pulsed laser rangefinder at different distances are obtained. When the actual jamming distance is farther than the minimum jamming distance, if the power is insufficient, there won’t be any jamming effect. When we continue to increase the power of the jamming laser in the successful jamming state, the minimum measured distance is still distributed around the blind area of the rangefinder, and ranging results tend to follow a normally distributed pattern. The bigger the power is, the distribution center will be closer to the minimum jamming distance which corresponds to laser’s frequency. When the jamming power is sufficient, the higher the jamming laser’s frequency is, the effective jamming range will be larger. Therefore, in practical engineering applications, it is necessary to improve the output power and frequency of jamming laser, the aiming accuracy of jamming equipment as much as possible.
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