  We present a stable dual-wavelength vortex beam carrying orbital angular
momentum (OAM) with two spectral peaks separated by a few terahertz in
diode-pumped Yb:CaGdAlO4 (CALGO) laser. The dual-wavelength spectrum is
controlled by the pump power and off-axis loss in laser resonator, arising from
the broad emission bandwidth of Yb:CALGO. The OAM beam is obtained by a pair of
cylindrical lens that serves as an {\pi}/2 convertor for the high-order
Hermite-Gaussian modes. The stability is verifed that the 1 h OAM beam with two
spectral peaks at 1046.1 nm and 1057.2 nm (3.01 THz interval) can steadily
operate for more than three hours. It has great potential for scaling the
application for OAM beams in Terahertz spectroscopy, high-resolution
interferometry, and so on.
