Frequency-mixed CO.sub.2 laser radar for remote detection of gases in the atmosphere

An improved system for the detection of one or more preselected gases in the atmosphere which comprises:

• a. CO.sub.2 laser beam means comprising:
• (1) a first CO.sub.2 laser source;
• (2) a second CO.sub.2 laser source;
• (3) crystal means for doubling the frequency of one of said laser sources;
• b. means for transmitting said CO.sub.2 laser means toward a target through the atmosphere which may contain gases which selectably absorb said laser beam at a preselected frequency;
• and
• c. means for detecting a reflected signal back from said target including means for determining signal strength;
• whereby the presence or absence of a preselected gas may be ascertained using a laser beam at a preselected frequency highly absorbable by the preselected gas and at another frequency not highly absorbed to determine the presence of the gas based on differences in signal strength of the reflected beams at the two frequencies.

An improved method for detecting the presence of one or more preselected gases in the atmosphere which comprises:

• a. generating a laser beam from a first laser beam source having a frequency in the infrared spectrum;
• b. doubling the frequency of said laser beam;
• c. generating a laser beam from a second laser beam source having a frequency in the infrared spectrum;
• d. adding the doubled frequency from one of said laser beams to the frequency of the other laser beam to obtain a laser beam at a third frequency;
• e. tuning at least one of said laser beams so that the third frequency produced by doubling one of the beam frequencies and adding it to the other frequency is a preselected frequency highly absorbed by said preselected gas;
• f. transmitting said highly absorbable third frequency laser beam through the atmosphere toward a reflecting target;
• g. detecting the reflected beam;
• h. retuning at least one of said lasers so that the resultant third frequency laser beam is not highly absorbed by said preselected gas;
• i. transmitting said resultant low absorption third frequency laser beam toward the same target;
• j. detecting the reflected signal from said low absorption laser beam;
• and
• k. comparing the strength of the reflected highly absorbable laser beam with the reflected low absorption second laser beam to determine the amount of absorption of said first beam to thereby determine the presence or absence of said preselected gas in the atmosphere.