润色这句话：By a narrow slit 37mm long and 3mm wide on the reflector the pump light directly enters into the rod unabsorbed light reflected by the inner surface of the reflector and reabsorbed by the crysta

Through a narrow 37mm-long and 3mm-wide slit on the reflector, the pump light is able to directly enter the rod. Any unabsorbed light is then reflected by the inner surface of the reflector and reabsorbed by the crystal rod, resulting in a uniform distribution of pump light.