Apparatus and method for measuring concentration of pollutants in water

An apparatus for measuring a concentration of pollutants in water, comprising a passive Q-switched fiber laser, an evanescent field fiber and a spectrum apparatus;

• wherein the evanescent field fiber is disposed in a laser resonant cavity of the passive Q-switched fiber laser, and the passive Q-switched fiber laser is connected with the spectrum apparatus;
• the passive Q-switched fiber laser is configured to output an evanescent wave to a to-be-tested water sample after emitting a Q-switched pulse laser signal and transmitting the Q-switched pulse laser signal via the evanescent field fiber;
• the passive Q-switched fiber laser is further configured to output an output repetition frequency result of the passive Q-switched fiber laser based on an evanescent wave change caused by an absorption effect of the pollutants in the to-be-tested water sample to the evanescent wave and an output repetition frequency change of the passive Q-switched fiber laser due to the evanescent wave change;
• and
• the spectrum apparatus is configured to display the output repetition frequency result of the passive Q-switched fiber laser.