Mode-locked pulsed laser system and method

• US 20040017833A1
• Filed: 09/27/2002
• Published: 01/29/2004
• Est. Priority Date: 03/30/2000
• Status: Active Grant

• Current Assignee: National Institute of Standards and Technology (Government of the United States of America), The United States of America As Represented By The Secretary of Agriculture
• Original Assignee: National Institute of Standards and Technology (Government of the United States of America)
• Inventors: Jones, David J., Hall, John L., Cundiff, Steven T., Diddams, Scott A.
• Granted Patent: US 6,850,543 B2
• Time in Patent Office: Days
• US Class Current: 372/18
• CPC Class Codes: H01S 3/0805 by apertures, e.g. pin-holes or knife-edges
• CPC Class Codes: H01S 3/0811 incorporating a dispersive element, e.g. a prism for wavelength selection
• CPC Class Codes: H01S 3/1112 Passive mode locking
• CPC Class Codes: H01S 3/1307 Stabilisation of the phase
• CPC Class Codes: H01S 3/139 by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity length
• CPC Class Codes: H01S 3/1398 by using a supplementary modulation of the output
• CPC Class Codes: H01S 3/1625 titanium
• CPC Class Codes: H01S 3/1636 Al2O3 (Sapphire)

Abstract

Disclosed is a system and method for stabilizing the carrier-envelope phase of the pulses emitted by a femtosecond mode-locked laser by using the powerful tools of frequency-domain laser stabilization. Control of the pulse-to-pulse carrier-envelope phases was confirmed using temporal cross correlation. This phase stabilization locks the absolute frequencies emitted by the laser, which is used to perform absolute optical frequency measurements that were directly referenced to a stable microwave clock.

Claims

1. A method of stabilizing the phase of a carrier wave signal with respect to an envelope of the pulses emitted by a mode-locked pulsed laser comprising:

obtaining an optical output from said pulsed laser that has a bandwidth that spans at least one octave;

separating a first frequency output from said optical output having a first frequency;

separating a second frequency output from said optical output, said second frequency output having a second frequency that is twice the frequency of said first frequency;

frequency doubling said-first frequency output of said pulsed laser to produce a frequency doubled first output;

frequency shifting said second frequency output by a predetermined amount to produce a second frequency shifted output;

combining said frequency doubled first output and said second frequency shifted output to obtain a beat frequency signal;

detecting said beat frequency signal;

using said beat frequency signal to phase coherently stabilize said phase of said carrier wave signal relative to said envelope of said pulsed laser.

2. The method of claim 1 wherein said step of frequency shifting said second frequency output by a predetermined amount to produce a second frequency shifted output further comprises applying an adjustable frequency input signal to an acousto-optic modulator that adjusts said second frequency shifted output by a fractional portion of the repetition frequency of said envelope.

3. The method of claim 1 wherein said step of frequency shifting said second frequency output by a predetermined amount to produce a second frequency shifted output further comprises applying an adjustable electric signal to an electro optic modulator.

15. The method of claim 1, 4, or 14 wherein said step of using said beat frequency signal to stabilize said phase of said carrier wave signal relative to said envelope of said pulsed laser further comprises:

generating control signals in response to said beat frequency to modify the optical cavity of said pulsed laser to change the velocity of said envelope and said carrier wave signal in said optical cavity.

16. The method of claim 15 wherein said step of modifying said optical cavity of said pulsed laser further comprises:

inserting prisms in said optical cavity that spatially disperse the spectrum of said carrier wave signal;

translating at least one of the mirrors of said laser cavity in response to said control signals;

tilting the mirror in said laser cavity that reflects said spatially dispersed spectrum in response to said control signal.

17. The method of claim 1, 4, or 14 wherein said predetermined amount is coherently derived from the repetition frequency of said pulsed laser.

18. The method of claim 1, 4, or 14 wherein said step of obtaining an optical output from said pulsed laser further comprises broadening said optical output from said pulsed laser using an optical fiber located externally from said optical cavity of said pulsed laser.

19. The method of claim 1, 4, or 14 wherein said step of obtaining an optical output from said pulsed laser further comprises generating a broadened optical output from said pulsed laser.

4. A method of stabilizing the phase of a carrier wave signal with respect to an envelope of the pulses emitted by a mode-locked pulsed laser comprising:

obtaining an optical output from said pulsed laser that has a bandwidth that spans at least one octave;

separating a first frequency output from said optical output having a first frequency;

separating a second frequency output from said optical output, said second frequency output having a second frequency that is twice the frequency of said first frequency;

frequency doubling said first frequency output of said pulsed laser to produce a frequency doubled first output;

frequency shifting said frequency doubled first output by a predetermined amount to produce a frequency doubled and shifted first output;

combining said second frequency output and said frequency doubled and shifted first output to obtain a beat frequency signal;

detecting said beat frequency signal;

using said beat frequency signal to phase coherently stabilize said phase of said carrier wave signal relative to said envelope of said pulsed laser.

5. The method of claim 4 wherein said step of frequency shifting said frequency doubled first output by a predetermined amount to produce a frequency doubled and shifted first output further comprises applying an adjustable acoustic signal to an acousto-optic modulator.

6. The method of claim 4 wherein said step of frequency shifting said frequency doubled first output by a predetermined amount to produce a frequency doubled and shifted first output further comprises applying an adjustable electric signal to an electro optic modulator.

7. A method of stabilizing the phase of a carrier wave signal with respect to an envelope of the pulses emitted by a mode-locked pulsed laser comprising:

obtaining an optical output from said pulsed laser that has a bandwidth that spans at least one octave;

separating a first frequency output from said optical output having a first frequency;

separating a second frequency output from said optical output, said second optical frequency output having a second frequency that is twice the frequency of said first frequency;

frequency doubling said first frequency output of said pulsed laser to produce a frequency doubled first output;

frequency shifting one of said frequency doubled first output and said second frequency, output by a predetermined amount to produce a frequency shifted output;

combining one of said frequency doubled first output and said second frequency output with said frequency shifted output to obtain a beat frequency signal;

detecting said beat frequency signal;

using said beat frequency signal to stabilize said phase of said carrier wave signal relative to said envelope of said pulsed laser.

8. A method of stabilizing the phase of a carrier wave signal with respect to an envelope of the pulses emitted by a mode-locked pulsed laser comprising:

obtaining an optical output from said pulsed laser that has a bandwidth that spans at least one octave;

separating a first frequency output from said optical output having a first frequency;

separating a second frequency output from said optical output, said second frequency output having a second frequency that is twice the frequency of said first frequency;

frequency shifting said first frequency output by a predetermined amount to produce a frequency shifted first output;

frequency doubling said frequency shifted first output of said pulsed laser to produce a frequency shifted and doubled first output;

combining said second frequency output and said frequency shifted and doubled first output to obtain a beat frequency signal;

detecting said beat frequency signal;

using said beat frequency signal to phase coherently stabilize said phase of said carrier wave signal relative to said envelope of said pulsed laser.

9. A mode-locked pulsed laser system that stabilizes the phase of a carrier wave signal with respect to an envelope of the pulses emitted by said mode-locked pulsed laser system comprising:

a mode-locked pulsed laser that generates an optical output;

a beam splitter that separates a first frequency signal from said optical output, having a first frequency, from a second frequency signal of said optical output, said second frequency signal having a second frequency that is twice the frequency of said first frequency;

a frequency doubler aligned with said first frequency signal that produces a frequency doubled first signal;

a frequency shifter aligned with said second frequency signal that frequency shifts said second frequency signal by a predetermined amount to produce a second frequency shifted signal;

a beam combiner that combines said frequency doubled first signal and said second frequency shifted signal to obtain a beat frequency signal;

a detector aligned to detect said beat frequency signal;

a control signal generator that generates control signals in response to said beat frequency signal;

a servo-controller that modifies the optical cavity of said pulsed laser in response to said control signals to change the relative velocity of said envelope and said carrier wave signal in said optical cavity.

10. The system of claim 9 further comprising:

a non-linear self-phase modulator that broadens the bandwidth of said optical output of said pulsed laser to a bandwidth that spans at least one octave.

11. The system of claim 9 or 10 wherein said non-linear self-phase modulator comprises an air-silica micostructure optical fiber.

12. The system of claim 9 or 10 wherein said frequency doubler comprises:

a -barium-borate frequency doubling crystal.

13. The system of claim 9 wherein the mode-locked pulsed laser generates an optical output that has bandwidth that spans at least one octave.

24. The system of claim 9, 10, or 22 wherein said beam splitter comprises:

a dichroic mirror.

25. The system of claim 9, 10, or 22 wherein said frequency shifter comprises:

an acousto-optic modulator.

26. The system of claim 9, 10, or 22 wherein said control device comprises:

carrier-envelope phase locking electronics.

27. The system of claim 9, 10, or 22 wherein said detector comprises:

an avalanche photodiode.

28. The system of claim 9, 10, or 22 wherein said servo-controller comprises:

a piezoelectric transducer tube that provides both tilt and translation.

14. A method of stabilizing the phase of a carrier wave signal with respect to an envelope of the pulses emitted by a mode-locked pulsed laser comprising:

obtaining an optical output from said pulsed laser that has a bandwidth that spans less than one octave;

separating a first frequency output from said optical output having a first frequency;

separating a second frequency output from said optical output, having a second frequency;

multiplying said first frequency output of said pulsed laser by an integer value N that is at least equal to 2 to produce a frequency multiplied first output;

multiplying said second frequency output of said pulsed laser by N−

1 to produce a frequency multiplied second output;

frequency shifting said frequency multiplied second output by a predetermined amount to produce a frequency multiplied second frequency shifted output;

combining said frequency multiplied first output and said frequency multiplied second frequency shifted output to obtain a beat frequency signal;

detecting said beat frequency signal;

using said beat frequency signal to phase coherently stabilize said phase of said carrier wave signal relative to said envelope of said pulsed laser.

20. The method of claim 14 wherein said step of frequency shifting said frequency multiplied second frequency output by a predetermined amount to produce a frequency multiplied second frequency shifted output further comprises applying an adjustable frequency input signal to an acousto-optic modulator that adjusts said frequency multiplied second frequency shifted output by a fractional portion of the repetition frequency of said envelope.

21. The method of claim 14 wherein said step of frequency shifting said frequency multiplied second frequency output by a predetermined amount to produce a frequency multiplied second frequency shifted output further comprises applying an adjustable electric signal to an electro optic modulator.

22. A mode-locked pulsed laser system that stabilizes the phase of a carrier wave signal with respect to an envelope of the pulses emitted by said mode-locked pulsed laser system comprising:

a mode-locked pulsed laser that generates an optical output;

a beam splitter that separates a first frequency signal from said optical output, having a first frequency, from a second frequency signal of said optical output, said second frequency signal having a second frequency;

a first frequency multiplier aligned with said first frequency signal that multiplies said first frequency signal by an integer value N that is at least equal to 2 to produce a frequency multiplied first signal;

a second frequency multiplier aligned with said second frequency signal that multiplies said second frequency signal by N−

1 to produce a frequency multiplied second signal;

a frequency shifter aligned with said frequency multiplied second frequency signal that frequency shifts said frequency multiplied second frequency signal by a predetermined amount to produce a frequency multiplied second frequency shifted signal;

a beam combiner that combines said frequency multiplied first signal and said frequency multiplied second frequency shifted signal to obtain a beat frequency signal;

a detector aligned to detect said beat frequency signal;

a control signal generator that generates control signals in response to said beat frequency signal;

a servo-controller that modifies an optical cavity of said pulsed laser in response to said control signals to change relative velocity between said envelope and said carrier wave signal in said optical cavity.

23. The system of claim 22 further comprising a non-linear self-phase modulator that broadens the bandwidth of said optical output to produce said predetermined bandwidth.