Miniaturized spectroscopy systems that can detect trace concentrations at the parts-per-billion (ppb) level are of the utmost importance in applications ranging from environmental monitoring and industrial process control to biomedical diagnostics. However, the existing bench-top spectroscopy systems are too large, complex, and impractical for narrow-space use. Furthermore, the traditional laser spectroscopy techniques use bulky components like light sources, mirrors, detectors, and gas cells to detect light absorbed or scattered by a sample, which makes them unsuitable for scenarios calling for minimal invasiveness such as intravascular diagnosis.