Laser frequency stabilizer using transient spectral hole burning

• US 6,654,394 B1
• Filed: 07/17/2002
• Issued: 11/25/2003
• Est. Priority Date: 07/01/1999
• Status: Expired due to Fees

• Current Assignee: Montana State University
• Original Assignee: Research and Development Institute, Inc.
• Inventors: Sellin, Peter B., Carlsten, John L., Strickland, Nicholas M., Cone, Rufus L.
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US10/019,429
• Time in Patent Office: 496 Days
• Field of Search: 372/26, 372/32, 372/29.02, 372/28, 372/18
• US Class Current: 372/32
• CPC Class Codes: H01S 3/1392 by using a passive reference, e.g. absorption cell H01S3/1396, H01S3/1398 take precedence
• CPC Class Codes: H01S 3/1394 by using an active reference, e.g. second laser, klystron or other standard frequency source
• CPC Class Codes: H01S 3/1398 by using a supplementary modulation of the output
• CPC Class Codes: H01S 5/0623 using the beating between two closely spaced optical frequencies, i.e. heterodyne mixing
• CPC Class Codes: H01S 5/065 Mode locking; Mode suppression; Mode selection ; Self pulsating
• CPC Class Codes: H01S 5/0657 Mode locking, i.e. generation of pulses at a frequency corresponding to a roundtrip in the cavity
• CPC Class Codes: H01S 5/0687 Stabilising the frequency of the laser

Abstract

Techniques for stabilizing a laser at a selectable frequency include splitting an output beam from an electrically adjustable laser into a first beam and a second beam. The second beam is transmitted through a modulator. Then the second beam is transmitted through a transient spectral hole burning material onto a detector. The laser is electronically adjusted in response to a detector output from the detector which senses the changes in the modulated second beam after it passes through the transient spectral hole burning material.

Additions here to encompass the mode-locked case?

Claims

1. A method for stabilizing a laser at a selectable frequency, the method comprising the steps of:

outputting a beam from a frequency adjustable laser at a selected frequency;

splitting the output beam into a first beam and a second beam, the first beam to be used in a separate application after the frequency adjustable laser is stabilized at the selected frequency, the second beam to be used for stabilizing the frequency adjustable laser at the selected frequency;

transmitting the second beam through a spectral hole burning material having an inhomogeneously broadened absorption line and capable of supporting a transient spectral hole or holes for a lifetime characteristic of the spectral hole burning material, the transient spectral hole in the inhomogeneously broadened absorption being used as a frequency and/or phase reference, and at least one of the spectrum, amplitude and phase of the second beam being modified via interaction with the spectral hole burning material;

transmitting the second beam, after passing through the spectral hole burning material, onto a detector to provide an electrical signal output of sensed changes in the second beam; and

adjusting the laser via feedback control, according to an adjusting signal derived from the electrical signal output from the detector, to stabilize the frequency adjustable laser at the selected frequency.

2. The method of claim 1, comprising the additional step of preparing the spectral hole burning material for transient spectral hole burning before transmitting the second beam through the spectral hole burning material.

3. The method of claim 2, wherein the step of preparing the spectral hole burning material comprises population storage in the excited state of an optically active ion.

4. The method of claim 2, wherein the step of preparing the spectral hole burning material comprises population storage in the intermediate state of an optically active ion.

5. The method of claim 2, wherein the step of preparing the spectral hole burning material comprises population storage in the excited state of an optically active molecule.

6. The method of claim 2, wherein the step of preparing the spectral hole burning material comprises population storage in the intermediate state of an optically active molecule.

7. The method of claim 1, comprising the additional step of:

modulating the second beam before transmitting the second beam through the spectral hole burning material;

wherein

deriving the adjusting signal from the electrical signal output from the detector includes filtering the electrical signal to generate the error signal, and demodulating the error signal to provide a demodulated error signal, the

frequency adjustable laser is adjusted using the demodulated error signal.

8. The method of claim 7, wherein the modulating of the second beam is out of phase with the demodulating of the error signal.

9. The method of claim 8, wherein the demodulated electrical signal comprises:

a first component attributed to at least one transient spectral hole; and

a second component not attributed to the at least one transient spectral hole.

10. The method of claim 9, wherein the second component is attributed to the inhomogeneous broadened absorption line of the spectral hole burning material.

11. The method of claim 10, wherein the step of adjusting the laser according to the electrical signal includes adjusting the laser according to the first component and the second component.

12. The method of claim 1, wherein the adjustable laser is a mode-locked laser.

13. The method of claim 1, wherein the adjustable laser is a single mode laser.

14. A laser stabilization device, comprising:

a frequency adjustable laser;

a beam splitter for splitting the beam from the frequency adjustable laser into a first beam and a second beam, the first beam being output to a separate application after the frequency adjustable laser is stabilized at a selected frequency;

a transient spectral hole burning material receiving the second beam and having an inhomogeneously broadened absorption line and capable of supporting a transient spectral hole or holes for a lifetime characteristic of the spectral hole burning material, the transient spectral hole in the inhomogeneously broadened absorption line providing a frequency and/or phase reference, and at least one of the spectrum, amplitude and phase of the second beam being modified via interaction with the spectral hole burning material;

a detector configured to sense the changes in the second beam after passing through the transient spectral hole burning material and output an electrical signal of the sensed changes; and

servo electronics for stabilizing the frequency adjustable laser at the selected frequency in response to an adjusting signal derived from the electrical signal output from the detector.

15. The laser stabilization device of claim 14, wherein the frequency adjustable laser is a single mode laser.

16. The laser stabilization device of claim 14, wherein the frequency adjustable laser is a mode-locked laser.

17. The laser stabilization device of claim 14, further comprising:

a modulator for modulating the second beam; and

a demodulator for demodulating the electrical signal output from the detector.

18. The laser stabilization device of claim 17, wherein the modulator and the demodulator operate at the same frequency and a different phase.

19. The laser stabilization device of claim 17, wherein the electrical signal comprises:

a first component attributed to at least one spectral hole; and

a second component not attributed to the at least one spectral hole.

20. The laser stabilization device of claim 17, wherein the modulator and the demodulator operate at a different frequency and different phase.