COMPACT MID-IR LASER

• US 20110103414A1
• Filed: 01/10/2011
• Published: 05/05/2011
• Est. Priority Date: 06/15/2005
• Status: Active Grant

• Current Assignee: David F. Amone, Timothy Day
• Original Assignee: David F. Amone, Timothy Day
• Inventors: Day, Timothy, Amone, David F.
• Granted Patent: US 8,050,307 B2
• Time in Patent Office: Days
• US Class Current: 372/25
• CPC Class Codes: B82Y 20/00 Nanooptics, e.g. quantum optics or photonic crystals
• CPC Class Codes: G02B 3/00 Simple or compound lenses
• CPC Class Codes: G02B 7/023 permitting adjustment
• CPC Class Codes: H01S 5/005 Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping H01S5/026, H01S5/18388 take precedence
• CPC Class Codes: H01S 5/02216 Butterfly-type, i.e. with electrode pins extending horizontally from the housings
• CPC Class Codes: H01S 5/02325 Mechanically integrated components on mount members or optical micro-benches
• CPC Class Codes: H01S 5/02415 by using a thermo-electric cooler [TEC], e.g. Peltier element
• CPC Class Codes: H01S 5/02492 CuW heat spreaders
• CPC Class Codes: H01S 5/0427 for applying modulation to the laser
• CPC Class Codes: H01S 5/06226 Modulation at ultra-high frequencies
• CPC Class Codes: H01S 5/3401 having no PN junction, e.g. unipolar lasers, intersubband lasers, quantum cascade lasers

Abstract

A compact mid-IR laser device utilizes a quantum cascade laser to provide mid-IR frequencies suitable for use in molecular detection by signature absorption spectra. The compact nature of the device is obtained owing to an efficient heat transfer structure, the use of a small diameter aspheric lens and a monolithic assembly structure to hold the optical elements in a fixed position relative to one another. The compact housing size may be approximately 20 cm×20 cm×20 cm or less. Efficient heat transfer is achieved using a thermoelectric cooler TEC combined with a high thermal conductivity heat spreader onto which the quantum cascade laser is thermally coupled. The heat spreader not only serves to dissipate heat and conduct same to the TEC, but also serves as an optical platform to secure the optical elements within the housing in a fixed relationship relative on one another. A small diameter aspheric lens may have a diameter of 10 mm or less and is positioned to provided a collimated beam output from the quantum cascade laser. The housing is hermetically sealed to provide a rugged, light weight portable MIR laser source.

Claims

1. A mid-IR (MIR) laser device comprising:

a quantum cascade laser that generates light output;

an optical lens that collimates the light output from the quantum cascade laser;

a thermo electric cooling (TEC) device; and

a monolithic heat spreader secured to the TEC device, the heat spreader retaining the quantum cascade laser and the optical lens, the heat spreader having a thermal conductivity of at least approximately 220 W/mK, the heat spreader serving to distribute heat to the TEC device from the quantum cascade laser and also serving as an optical platform to fixedly position the quantum cascade laser and the optical lens relative to one another.

2. The MIR laser device of claim 1 wherein the heat spreader includes a bottom surface that is mounted to a top surface of the TEC device, and wherein the bottom surface of the heat spreader is approximately the same size as the top surface of the TEC device so that heat is distributed over the entire top surface of the TEC device.

3. The MIR laser device of claim 1 wherein the optical lens has numerical aperture that is greater than approximately 0.6, a diameter of less than approximately 5 millimeters, and a focal length of less than approximately 5 millimeters.

4. The MIR laser device of claim 3 wherein the optical lens is made of a material selected from the group consisting of Ge, ZnSe, ZnS Si, CaF, BaF, and chalcogenide glass

5. The MIR laser device of claim 1 further comprising a housing that encloses the quantum cascade laser, the optical lens, the TEC device and the heat spreader;

the housing having dimensions of less than approximately 20 centimeters by 20 centimeters by 20 centimeters.

6. The MIR laser device of claim 5 wherein the housing has dimensions of less than approximately 3 centimeters by 4 centimeters by 6 centimeters.

7. The MIR laser device of claim 1 further comprising a high thermal conductivity sub-mount positioned between the quantum cascade laser and the heat spreader, the sub-mount having a thermal conductivity of between approximately 500-2000 W/mK.

8. The MIR laser device of claim 1 further comprising an electronics sub-assembly comprising:

a switch contained within the housing;

an summing node, contained within the housing;

an RF input port for inputting an RF modulating signal;

a drive current input terminal electrically connected to the quantum cascade laser for inputting drive current to the quantum cascade laser;

a switching control signal input terminal for inputting a switching control signal for switching the switch between a first and second state;

the switch electrically connected to the quantum cascade laser and operative in a first state to turn the quantum cascade laser on and in a second state operative to turn the quantum cascade laser off;

the summing node interposed in an electrical path between the drive current input terminal and the quantum cascade laser to add the RF modulating signal to the drive current.

9. The MIR laser device of claim 1 further comprising a switch electrically connected to the quantum cascade laser and operative to turn the quantum cascade laser on and to turn the quantum cascade laser off in a pulsing fashion.

10. The MIR laser device of claim 1 wherein the operation of the quantum cascade laser generates at least approximately ten watts of heat output, and wherein the TEC device can control the temperature of the quantum cascade laser to be approximately room temperature.

11. The MIR laser device of claim 1 wherein the quantum cascade laser includes end facets with reflecting mirrors built into the end facets.

14. The MIR laser device of claim 1 wherein the optical lens has a numerical aperture that is greater than approximately 0.6, a diameter of less than approximately 5 millimeters, and a focal length of less than approximately 5 millimeters.

12. A mid-IR (MIR) laser device comprising:

a quantum cascade laser that generates light output;

a switch electrically connected to the quantum cascade laser and operative to turn the quantum cascade laser on and to turn the quantum cascade laser off in a pulsing fashion;

an optical lens that collimates the light output from the quantum cascade laser;

a thermo electric cooling (TEC) device, the TEC device having a top surface;

a monolithic heat spreader secured to the TEC device, the heat spreader retaining the quantum cascade laser and the optical lens, the heat spreader having a thermal conductivity of at least approximately 220 W/mK, the heat spreader serving to distribute heat to the TEC device from the quantum cascade laser and also serving as an optical platform to fixedly position the quantum cascade laser and the optical lens relative to one another, the heat spreader including a bottom surface that is mounted to the top surface of the TEC device, and wherein the bottom surface of the heat spreader is approximately the same size as the top surface of the TEC device so that heat is distributed over the entire top surface of the TEC device;

a high thermal conductivity sub-mount positioned between the quantum cascade laser and the heat spreader, the sub-mount having a thermal conductivity of between approximately 500-2000 W/mK; and

a housing that encloses the quantum cascade laser, the optical lens, the TEC device, the switch, the sub-mount, and the heat spreader;

the housing having dimensions of less than approximately 20 centimeters by 20 centimeters by 20 centimeters;

wherein the operation of the quantum cascade laser generates at least approximately ten watts of heat output, and wherein the TEC device can control the temperature of the quantum cascade laser to be approximately room temperature.

13. The MIR laser device of claim 12 wherein the quantum cascade laser includes end facets with reflecting mirrors built into the end facets.

15. A method for generating light output, the method comprising the steps of:

directing power to a quantum cascade laser to generate light output;

collimating the light output from the quantum cascade laser with an optical lens;

removing heat from the quantum cascade laser with a thermo electric cooling (TEC) device; and

retaining the quantum cascade laser and the optical lens with a monolithic heat spreader that also serves as an optical platform to fixedly position the quantum cascade laser and the optical lens relative to one another, the heat spreader being secured to the TEC device, the heat spreader having a thermal conductivity of at least approximately 220 W/mK.

16. The method of claim 15 wherein the step of retaining includes the heat spreader having a bottom surface that is mounted to a top surface of the TEC, and wherein the bottom surface of the heat spreader is approximately the same size as the top surface of the TEC device so that heat is distributed over the entire top surface of the TEC device.

17. The method of claim 15 wherein the step of collimating the light output includes the optical lens being made of a material selected from the group consisting of Ge, ZnSe, ZnS Si, CaF, BaF, and chalcogenide glass.

18. The method of claim 15 further comprising the step of retaining the heat spreader, the laser, and the optical lens with a housing having dimensions of less than approximately 20 centimeters by 20 centimeters by 20 centimeters.

19. The method of claim 15 further comprising the step of positioning a high thermal conductivity sub-mount between the laser and the heat spreader, the sub-mount having a thermal conductivity of approximately 500-2000 W/mK.

20. The method of claim 15 further comprising the step of turning the quantum cascade laser on and off in a pulsing fashion.