Temperature control system for a frequency converted diode laser

• US 8,238,389 B2
• Filed: 02/25/2011
• Issued: 08/07/2012
• Est. Priority Date: 06/15/2005
• Status: Active Grant

• Current Assignee: Idex Health & Science LLC (RELX PLC)
• Original Assignee: CVI Laser LLC
• Inventors: Hargis, David E., Vadnais, Neil E., O'Shaughnessy, John, Takeuchi, Eric B., Paterson, Scott
• Primary Examiner(s): Stultz, Jessica
• Assistant Examiner(s): FORDE, DELMA ROSA
• Application Number:
  US13/035,727
• Publication Number:
  US 20110188523A1
• Time in Patent Office: 529 Days
• Field of Search: 372/21, 372/22, 372/28, 372/29.02, 372/29.021, 372/92, 372/102
• US Class Current: 372/21
• CPC Class Codes: G02F 1/3775 with a periodic structure, e.g. domain inversion, for quasi-phase-matching [QPM] G02F1/383 takes precedence
• CPC Class Codes: H01S 2301/02 ASE (amplified spontaneous emission), noise; Reduction thereof
• CPC Class Codes: H01S 5/0092 for nonlinear frequency conversion, e.g. second harmonic generation [SHG] or sum- or difference-frequency generation outside the laser cavity
• CPC Class Codes: H01S 5/024 Arrangements for thermal management
• CPC Class Codes: H01S 5/02415 by using a thermo-electric cooler [TEC], e.g. Peltier element
• CPC Class Codes: H01S 5/02446 Cooling being separate from the laser chip cooling
• CPC Class Codes: H01S 5/0612 controlled by temperature
• CPC Class Codes: H01S 5/0683 by monitoring the optical output parameters
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser
• CPC Class Codes: H01S 5/146 using a fiber as external cavity

Abstract

Apparatus and methods of controlling a frequency-converted diode laser system are disclosed. The diode laser systems can include embodiments of thermally coupled elements facilitating temperature stabilization. Aspects of some methods include monitoring the output of a stabilized diode laser system to reduce noise of the output laser beam. Other aspects of some methods include adjusting the temperature of a frequency converter based on noise in the output beam, and/or the current provided to drive the diode laser. Systems incorporating such control aspects, and others, are also disclosed.

Claims

1. A frequency converted laser system, comprising:

a laser system configured to produce a laser beam having a first frequency, said laser system comprising an optical medium comprising a Bragg grating;

a waveguide comprising at least one nonlinear material, said waveguide being configured to receive an input laser beam of a first frequency from said diode laser system and emit an output laser beam having a second frequency, the second frequency different than the first frequency;

a power control system optically coupled with said waveguide and configured to monitor said output laser beam, said power control system being configured to provide a first signal indicative of noise in said output laser beam;

a temperature control system connected to said power control system to receive said first signal, said temperature control system comprising

a first temperature controlled element connected to said waveguide for controlling a temperature of the waveguide, and

a controller configured to control the temperature of said temperature controlled element,

wherein said temperature control system is configured to adjust the temperature of said first temperature controlled element to reduce noise in said output laser beam based on said first signal; and

a thermal connector connected to said first temperature controlled element and connected to at least a portion of said optical medium comprising said Bragg grating, said thermal connector thermally coupling said first temperature controlled element and said Bragg grating such that the temperature of said Bragg grating is related to the temperature of said first temperature controlled element.

2. The frequency converted laser system of claim 1, wherein said power control system is further configured to derive said first signal based on an AC component in said output laser beam indicating a noise level in said output laser beam.

3. The frequency converted laser system of claim 2, wherein said temperature control system is configured to adjust the temperature of said first temperature control element when the first signal indicates the noise level is greater than a predetermined threshold value.

4. The frequency converted laser system of claim 1, wherein the laser system comprises a fiber Bragg grating stabilized laser, and wherein said optical medium comprises optical fiber.

5. The frequency converted laser system of claim 1, wherein the laser system comprises an external cavity diode laser.

6. The frequency converted laser system of claim 5, wherein the external cavity diode laser comprises a volume Bragg grating.

7. The frequency converted laser system of claim 1, where the temperature controlled element comprises a thermo-electric cooler.

8. A frequency converted laser system, comprising:

a laser system configured to produce a laser beam having a first frequency, said laser system comprising an optical medium comprising a Bragg grating;

a waveguide comprising at least one nonlinear material, said waveguide being configured to receive an input laser beam of a first frequency from said diode laser system and emit an output laser beam having a second frequency, the second frequency different than the first frequency;

a power control system optically coupled with said waveguide and configured to monitor said output laser beam, said power control system being configured to provide a first signal indicative of noise in said output laser beam;

a temperature control system connected to said power control system to receive said first signal, said temperature control system comprising

a first temperature controlled element connected to said waveguide for controlling a temperature of the waveguide, and

a controller configured to control the temperature of said temperature controlled element,

wherein said temperature control system is configured to adjust the temperature of said first temperature controlled element to reduce noise in said output laser beam based on said first signal;

a second temperature controlled element; and

a thermal connector connected to at least a portion of said optical medium having said Bragg grating, said thermal connector thermally coupling said second temperature controlled element and said Bragg grating such that the temperature of said Bragg grating is related to the temperature of said second temperature controlled element.

9. A frequency converted laser system, comprising:

a laser system configured to produce a laser beam having a first frequency, said laser system comprising an optical medium comprising a Bragg grating;

a waveguide comprising at least one nonlinear material, said waveguide being configured to receive an input laser beam of a first frequency from said laser system and emit an output laser beam having a second frequency, the second frequency different than the first frequency;

a power control system optically coupled with said waveguide and configured to monitor said output laser beam, said power control system being configured to provide a first signal indicative of power in said output laser beam;

a diode control system connected to said power control system to receive said first signal, said diode control system configured to control a drive current supplied to drive said laser system based on said first signal; and

a temperature control system connected to said diode control system to receive a second signal indicative of said drive current level, said temperature control system comprising

a first temperature controlled element connected to said waveguide for controlling the temperature of the waveguide, and

a controller configured to control the temperature of said temperature controlled element,

wherein said temperature control system is configured to adjust the temperature of said first temperature controlled element to reduce said drive current.

10. The frequency converted laser system of claim 9, wherein the temperature control system is configured to adjust the temperature when said second signal indicates said drive current has increased by a predetermined amount from a previously indicated drive current level.

11. The frequency converted laser system of claim 9, wherein said temperature control system is further configured to adjust the temperature by changing the temperature of said waveguide in a first direction and observing a change in said drive current as indicated by said second signal, and if a reduction in said drive current is observed then continuing to change the temperature of the waveguide in the first direction until the drive current is below a threshold value, and if a reduction in said drive current is not observed, then adjusting the temperature of said waveguide in a second direction, opposite the first direction, and if a decrease said drive current is observed, then continuing to change the temperature of the waveguide in the second direction until said drive current is below said threshold value.

12. The frequency converted laser system of claim 9, wherein the laser system comprises a fiber Bragg grating stabilized laser, and wherein said optical medium comprises optical fiber.

13. The frequency converted laser system of claim 9, wherein the laser system comprises an external cavity diode laser.

14. The frequency converted laser system of claim 13, wherein the external cavity diode laser comprises a volume Bragg grating.

15. A method for reducing noise in a laser system having a frequency converter, comprising:

monitoring a frequency converted output laser beam;

detecting a noise component of said output laser beam;

determining a noise value indicative of said noise component; and

adjusting a temperature of the frequency converter to reduce said noise value, wherein adjusting the temperature comprises

if said noise value exceeds a noise threshold value, adjusting the temperature of the frequency converter in a first direction and monitoring the change in said noise value, and if said noise value decreases, then continue to adjust the temperature in the first direction until an increase in said noise value is observed,

and if said noise value increases when adjusting the temperature in the first direction, adjusting the temperature in a second direction opposite the first direction and monitoring a second change in said noise value, and if a decrease in said noise value is observed, then continuing to change the temperature in the second direction until an increase in said noise value is observed.

16. The method of claim 15, wherein said noise component comprises an AC component in the output laser beam.

17. A method for operating a frequency-converted diode laser system, the method comprising:

monitoring a laser beam from the frequency converted diode laser system;

determining a power value indicative of the output power of said laser beam;

providing an amount of current to said laser diode system responsive to said power value such that said provided current amount maintains said output power at a predetermined level; and

if said current amount exceeds a threshold value, adjusting the temperature of a frequency converter to reduce said current amount while maintaining said output power at said predetermined level.

18. The method of claim 17, wherein said adjusting the temperature includes

changing the temperature of the frequency converter in a first direction and monitoring a first change in said current amount, and if a reduction in said current amount occurs, continuing to change the temperature of the frequency converter in the first direction until said current amount is no longer being reduced, and if a reduction in said current amount does not occur, then changing the temperature of the frequency converter in a second direction, opposite the first direction, and monitoring a second change in said current amount and if a decrease in said current amount occurs, then continuing to change the temperature of the frequency converter in the second direction and monitoring a change in the output power until said current amount is no longer reduced.

19. The method of claim 18, wherein said threshold value is about 5% above a previously provided low current amount.

20. The method of claim 18, wherein said threshold value is about 10% above a previously provided low current amount.

21. A method for reducing noise and efficiently operating a frequency converted laser system, the method comprising:

monitoring a frequency converted laser beam output;

monitoring an amount of current provided to drive said laser system to produce said laser beam output;

determining an AC component and a DC component of said monitored laser beam output, the magnitude of the AC component being indicative of output noise of said monitored laser beam output, and the DC component being indicative of power of said monitored laser beam output; and

adjusting a temperature of a frequency converter responsive to said AC component and said DC component to reduce the output noise of said laser beam output, and to reduce said amount of current.

22. A method of operating a frequency converted laser system laser controlled by a power control system that regulates drive current supplied to drive the laser system to produce a laser beam having consistent output power, the method comprising:

storing a first current value indicative of a low amount of said drive current used to produce a laser beam output having a first power level;

storing a temperature value indicative of the temperature of a frequency converter while producing the laser beam having said first power level;

monitoring a second current provided to the diode laser;

determining if a difference between said first current value and said second current exceeds a threshold value; and

if the difference exceeds the threshold value, adjusting the temperature of the frequency converter to reduce said drive current while maintaining said first power level of the laser beam output.