A system and method is proposed for chemicals detection such as explosives and others, which are based on sensing of trace gases associated with the chemical. This sensing includes detection of spectrum and relative concentration of the trace gases followed by the chemical identification based on these data. The sensing is based on photothermal interferometry method modified by implementation of coherent optical detection. This modification essentially improves the device performance by increasing its sensitivity and selectivity. Improved characteristics of the device allow remote sensing of the interrogated chemicals at a distance up to 1000 meters, which is crucial for explosives detection. The coherent optical detection is performed by a coherent receiver based on 90-degrees optical hybrid.