Ultra-short pulse laser and method for obtaining long-distance transmission laser

The invention discloses an ultra-short pulse laser and a method for obtaining long-distance transmission laser. The ultra-short pulse laser comprises a mode-locking oscillator, a stretcher, two amplifiers, a compressor and a controller that are arranged in the sequence of the amplifier, the stretcher, the amplifier and the compressor based on the transmission path of the laser generated by the mode-locking oscillator; the controller is connected with the stretcher or the compressor; the stretcher or the compressor is controlled through the controller to obtain outgoing laser with negative initial chirp value; the atmosphere has the positive dispersion, so that the laser is compressed constantly when the laser is transmitted in the atmosphere, and the peak power is increased constantly; by controlling the initial chirp value, a self-focusing threshold value is reached in the position of a target distance, and a smaller light spot and a higher power density are obtained in the position close to the self-focusing point, so that the purposes of the high power density in a long distance and a controllable transmission distance are realized.