Some spectroscopic applications require excitation light sources with dual-wavelength
laser emission. For example, in absorption spectroscopy one on-resonance and one off-resonance
wavelength are needed for concentration measurements. For shifted excitation Raman
difference spectroscopy (SERDS), two excitation wavelengths are used to distinguish
between disturbing light and Raman signals. In both cases an adjustable wavelength
spacing allows optimizing the measurements according to the spectral width of the
target. In addition, a tuning of the spectral distance also allows generating a tunable
sum or difference frequency signal, enabling further applications.In this paper, diode
lasers with customized designs according to the spectral requirements of the applications
will be presented. As basis for all devices, Y-branch diode lasers with an integrated
grating for wavelength stabilization are realized. The emission of the two branches
is combined in an implemented Y-shaped coupler. The bent waveguides are sine shaped
S-bends. The spectral tuning is performed via implemented heater elements next to
the Distributed Bragg Reflector (DBR) gratings or via the injection current when using
a Distributed Feedback (DFB) grating. Power-voltage current characteristics, spectral
and tuning properties will be shown.The devices emitting at 671 nm and 785 nm are
used for SERDS, whereas devices at 965 nm were tested as seed sources for pulsed master
oscillator power amplifiers (MOPA) suitable for the detection of water vapor.Devices
at 785 nm are also suitable for the generation of THz radiation using difference frequency
generation. A widely tunable Y-branch diode laser near 972 nm is used for the sum
frequency generation in an up-conversion system.
