  Frequency comb assisted diode laser spectroscopy, employing both the accuracy
of an optical frequency comb and the broad wavelength tuning range of a tunable
diode laser, has been widely used in many applications. In this letter we
present a novel method using cascaded frequency agile diode lasers, which
allows extending the measurement bandwidth to 37.4 THz (1355 to 1630 nm) at MHz
resolution with scanning speeds above 1 THz/s. It is demonstrated as a useful
tool to characterize a broadband spectrum for molecular spectroscopy and in
particular it enables to characterize the dispersion of integrated
microresonators up to the fourth order.
