Researchers are measuring the effect on a laser diode's frequency of optical feedback from a short cavity made from high-performance cylindrical microlens collimators. The microlens assembly, which circularizes and collimates the diode output radiation to a diffraction limited beam, also provides highly efficient optical feedback into the laser cavity. From the results of these experiments, researchers are designing a simple, low-cost, compact, and robust tunable diode laser system that utilizes collimating microlenses to form a short external cavity for both longitudinal mode control and frequency tuning.Commercial Applications:Research introduces very compact tunable laser diodes for a wide variety of scientific instruments. They can make some instruments portable and replace cumbersome, multi-element tunable lasers in scientific instruments.