  We present an external cavity diode laser setup using two identical,
commercially available interference filters operated in the blue wavelength
range around 450 nm. The combination of the two filters decreases the
transmission width, while increasing the edge steepness without a significant
reduction in peak transmittance. Due to the broad spectral transmission of such
interference filters compared to the internal mode spacing of blue laser
diodes, an additional locking scheme, based on H\"ansch-Couillaud locking to a
cavity, has been added to improve the stability. The laser is stabilized to a
line in the tellurium spectrum via saturation spectroscopy, and
single-frequency operation for a duration of two days is demonstrated by
monitoring the error signal of the lock and the piezo drive compensating the
length change of the external resonator due to air pressure variations.
Additionally, transmission curves of the filters and the spectra of a sample of
diodes are given.
