The cavity length of a CW mode-locked Nd:YLF laser is detuned to investigate the effect of detuning on the output of the laser. Negative detunings of 0.4 to 2.4 mu m result in periodic modulations of the pulse envelope. Further negative detunings of 2.4 to 3.4 mu m produce undamped regular spikings, that is, stable self-Q-switching behavior with mode-locked pulses of 30 approximately 47 ps pulsewidths, which are as short as those of plain mode locking without Q switching. Similar self-Q-switching behavior is also produced by positive detunings, but the stability is very poor. >