Mid-infrared light hydrocarbon dial lidar

• US 5,250,810 A
• Filed: 04/23/1992
• Issued: 10/05/1993
• Est. Priority Date: 06/18/1990
• Status: Expired due to Term

• Current Assignee: Lasen, Inc.
• Original Assignee: Lasen, Inc.
• Inventors: Geiger, Allen R.
• Primary Examiner(s): FIELDS, CAROLYN
• Application Number:
  US07/872,306
• Time in Patent Office: 530 Days
• Field of Search: 250/338.5, 250/339
• US Class Current: 250/338.5
• CPC Class Codes: G01N 21/3504 for analysing gases, e.g. multi-gas analysis
• CPC Class Codes: G01S 17/10 using transmission of interrupted, pulse-modulated waves determination of distance by phase measurements G01S17/32
• CPC Class Codes: G01S 17/95 for meteorological use
• CPC Class Codes: G01S 7/483 Details of pulse systems
• CPC Class Codes: Y02A 90/10 Information and communication technologies [ICT] supporting adaptation to climate change, e.g. for weather forecasting or climate simulation

Abstract

A DIAL LIDAR system, and methods of operating same are disclosed. A plurality, such as six, distinct coherent beams are combined into a single transmitted beam. Atmospheric targets, such as light hydrocarbons cause a portion of the transmitted beam to be reflected as a return. In one transmitting configuration, six pulsed beams are fully time-multiplexed, and are combined through selective polarization. In another transmitting configuration, six pulsed beams are fully time-multiplexed, and are combined through selective orientation of beam paths, in connection with a rotating beam displacer. In yet another transmitting configuration, six beams are wavelength-multiplexed, and are combined through differential refraction. In one receiving configuration, time-multiplexed beams are received using a single detector. In another receiving configuration, wavelength-multiplexed beams are received using multiple detectors. In a coherent LIDAR configuration, the outputs of a plurality of coherent sources are modulated, and combined according to any of the aforementioned transmitting configurations. A portion of the source outputs is directed to a receiver section of the system, where it is used to demodulate the LIDAR return.

Claims

1. A method of detecting light hydrocarbons in the atmosphere, comprising the following steps:

generating at lest two pairs of pulsed polarized beams by optical parametric oscillation with at least two tunable coherent light sources, each beam tuned to a different wavelength, each pair of beams having a common polarization state;

directing the polarized beams so that they are substantially located on a common optical axis;

transmitting the beams into the atmosphere;

receiving returns from light hydrocarbons in the atmosphere; and

analyzing the returns to determine the light hydrocarbon content in the atmosphere.

2. A method as defined in claim 1, wherein the pairs of beams are directed substantially along the common optical axis with a polarization combining beam splitter.

3. A method as defined in claim 1, wherein at least one pair of polarized beams has a different polarization state than at least one other pair of polarized beams.

4. Method according to claim 1 wherein:

the wavelengths of the pulsed beams are in the 3.1 to 3.5 micron range.

5. Method according to claim 4, wherein:

the wavelengths of at least two of the pulsed beams are in the 3.16 to 3.18 micron range.

6. Method according to claim 4, wherein:

the wavelengths of at least two of the pulsed beams are in the 3.37 to 3.5 micron range.

7. Method according to claim 1, wherein:

the wavelengths of at least two of the pulsed beams are in the 2.0 to 2.4 micron range.

8. A method of detecting light hydrocarbons in the atmosphere, comprising the following steps:

generating a plurality of beams with a plurality of coherent light sources, each beam having a different wavelength;

reflecting each beam along a predetermined path into a prism;

combining the beams in the prism and transmitting a single transmitting beam from the prism;

transmitting the single transmitting beam into the atmosphere;

receiving returns from light hydrocarbons in the atmosphere; and

analyzing the returns to determine the light hydrocarbon content in the atmosphere.

9. A method as defined in claim 8, wherein each beam is generated by optical parametric oscillation.