We have experimentally studied thermal effects in highly pumped Ti:sapphire
crystals in the 140-340 K temperature range. We demonstrate that a critica
l temperature exists, which depends on pumping and probing conditions, belo
w which detrimental thermal effects completely disappear. In particular, we
show that in a typical high-intensity Ti:sapphire amplifier, thermal lensi
ng and wave-front distortions can be suppressed keeping the crystal tempera
ture lower than similar to 230 K.