The dispersion produced by an ordinary single stack cavity mirror is analysed. This kind of mirror is difficult to compensate the upehirp of the pulses in the cavity. A kind of double ooated stack mirror, with the suitable amount of dispersion of φ(ω) =1.3 ×10~(-28) sec2 for upchirp compensation is designed and used as cavity mirrors, so that pulses as short as 30 fs are generated directly from a simple oolliding-pulse modo-locked (CPM) dye laser without additional dispersive elements in the cavity.