A method of light amplification, comprising:
- letting enter first pulsed light, and second pulsed light having a peak intensity greater than a peak intensity of the first pulsed light to a first optical fiber;
- and
- letting enter the first pulsed light, having exited the first optical fiber, to a second optical fiber to amplify, wherein
- a value of multiplication of nonlinearity of the first optical fiber and a length of the first optical fiber is greater than a value of multiplication of nonlinearity of the second optical fiber and a length of the second optical fiber.