  Experimental control and detection of atoms and molecules often rely on
optical transitions between different electronic states. In many cases,
substructure such as hyperfine or spin-rotation structure leads to the need for
multiple optical frequencies spaced by MHz to GHz. The task of creating
multiple optical frequencies -- optical spectral engineering -- becomes
challenging when the number of frequencies becomes large, a situation that one
could encounter in complex molecules and atoms in large magnetic fields. In
this work, we present a novel method to synthesize arbitrary optical spectra by
modulating a monochromatic light field with a time-dependent phase generated
through computer-generated holography techniques. Our method is compatible with
non-linear optical processes such as sum frequency generation and second
harmonic generation. Additional requirements that arise from the finite
lifetimes of excited states can also be satisfied in our approach. As a
proof-of-principle demonstration, we generate spectra suitable for cycling
photons on the X-B transition in CaF, and verify via Optical Bloch Equation
simulations that one can achieve high photon scattering rates, which are
important for fluorescent detection and laser cooling. Our method could offer
significant simplifications in future experiments that would otherwise be
prohibitively complex.
