Differential absorption laser radar gas detection apparatus having tunable wavelength single mode semiconductor laser source

A method for detecting a gas, said method comprising the steps of:

• providing light source means including a tunable wavelength single mode semiconductor laser, said tunable wavelength single mode semiconductor laser outputting a single mode laser beam having a wavelength tuned in accordance with a drive current to a first optical path and a second optical path, the semiconductor laser emitting, for an objected to be detected, at least a first laser beam having a first wavelength which is absorbed by a gas to be detected or a second laser beam having a second wavelength which is not absorbed by the gas to be detected;
• switching the drive current having a predetermined value corresponding to the first or the second wavelength at a predetermined period and supplying the drive current to said tunable wavelength single mode semiconductor laser by first control means, and controlling the drive current having the predetermined value corresponding to the first or the second wavelength so that the first and second laser beams are alternately output from said tunable wavelength single mode semiconductor laser with substantially the same power while the first and the second wavelengths are maintained;
• receiving the first and the second laser beams emitted from the tunable wavelength single mode semiconductor laser through the second optical path by first light-receiving means, and outputting detection signals corresponding to the wavelengths and powers of the received first and second laser beams;
• feeding back a correction signal for correcting the drive currents having the predetermined values to the first control means by second control means in accordance with the detection signal from the first light-receiving means;
• receiving first and second response light components generated when the first and the second laser beams emitted alternately from the tunable wavelength single mode semiconductor laser are incident on the object to be detected through the first optical path by second light-receiving means, and outputting electrical signals corresponding to received light amounts of the first and the second response light components;
• and
• receiving the electrical signals from the second light-receiving means by signal processing means, and processing a presence/absence condition of gas detection in accordance with a difference between the received light amounts of the first and the second response light components.

A gas detection apparatus, comprising:

• light source means including a tunable wavelength single mode semiconductor laser, said tunable wavelength single mode semiconductor laser including means for outputting a single mode laser beam having a wavelength tuned in accordance with a drive current and emitting, for an object to be detected, at least a first laser beam having a first wavelength which is absorbed by a gas to be detected or a second laser beam having a second wavelength which is not absorbed by the gas to be detected;
• control means for switching the drive current having a predetermined value corresponding to the first or the second wavelength at a predetermined period, and for supplying the drive current to said tunable wavelength single mode semiconductor laser, said control means including means for controlling the drive current having the predetermined value corresponding to the first or the second wavelength so that the first and the second laser beams are alternately output from said tunable wavelength single mode semiconductor laser with substantially the same power while the first and the second wavelengths are maintained;
• light-receiving means for receiving first and second response light components generated when the first and the second laser beams emitted alternately from said tunable wavelength single mode semiconductor laser are incident on the object to be detected, and for outputting electrical signals corresponding to received light amounts of the first and the second response light components wherein the first and the second response light components are transmitted through the object to be detected;
• signal processing means for receiving the electrical signals from said light-receiving means, and for processing a presence/absence condition of gas detection in accordance with a difference between the received light amounts of the first and the second response light components;
• transmitting means for storing at least said light source means;
• and
• receiving means for storing at least said light-receiving means;
• wherein said transmitting means and said receiving means include means for performing data communication using the second wavelength between one another.