We report a laser spectroscopy technique for detecting optical absorption in gases and micro-objects via linked thermal effects and by using a sharp mechanical resonance in a quartz crystal. The performance of this technique is studied using near-IR diode lasers and two gases, pure ${\mathrm{CO}}_2$ and ${\mathrm{C}}_2{\mathrm{H}}_2$ diluted in nitrogen. A $7.3\times {10}^{-8}{\mathrm{cm}}^{-1}\mathrm{W}/(\mathrm{Hz}{)}^{1/2}$ noise equivalent sensitivity to absorption in gases is demonstrated. Based on experimental results, it was estimated that ${10}^{-8}$ fractional absorption of optical radiation by a micro-object deposited on a thin transparent fiber can be detected.