  The threshold properties of photonic crystal quantum dot lasers operating in
the slow-light regime are investigated experimentally and theoretically.
Measurements show that, in contrast to conventional lasers, the threshold gain
attains a minimum value for a specific cavity length. The experimental results
are explained by an analytical theory for the laser threshold that takes into
account the effects of slow-light and random disorder due to unavoidable
fabrication imperfections. Longer lasers are found to operate deeper into the
slow-light region, leading to a trade-off between slow-light induced reduction
of the mirror loss and slow-light enhancement of disorder-induced losses.
