The Cr3+: LiSAF crystal is widely used as a laser medium of a wide gain spectrum from 700 nm to 920 nm. Our numerical investigations demonstrate a spectro-temporal evolution in the broadband Cr3+: LiSAF laser emission from Fabry-Perot resonator and particularly, from a low – Q resonator. Furthermore, the resonator transient and the phenomenon of relaxation oscillations in the solidstate Cr3+: LiSAF laser have been studied. Interestingly, using a diode-pump pulse of 100 μs at 670 nm, a stable generation of single nanosecond Cr3+: LiSAF laser pulse at 850 nm is obtainable by simple choices of resonator parameters such as photon-cavity time and pump level. A pulse compression factor of 1 000 is achievable. As a result, a simple technique of short laser pulse generation at a high repetition rate of diode pumping pulses has been proposed.