Generation of stabilized, ultra-short light pulses and the use thereof for synthesizing optical frequencies

• US 6,785,303 B1
• Filed: 07/29/2002
• Issued: 08/31/2004
• Est. Priority Date: 03/12/1999
• Status: Expired due to Term

• Current Assignee: Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften e.V. (Max-Planck-Gesellschaft zur Frderung der Wissenschaften e)
• Original Assignee: Max-Planck-Gesellschaft Zur Foerderung Der Wissenschaften e.V. (Max-Planck-Gesellschaft zur Frderung der Wissenschaften e)
• Inventors: Udem, Thomas, Reichert, Jörg, Hänsch, Theodor W., Holzwarth, Ronald
• Primary Examiner(s): Ip, Paul
• Assistant Examiner(s): AL NAZER, LEITH A
• Application Number:
  US09/936,388
• Time in Patent Office: 764 Days
• Field of Search: 372/16, 372/18, 372/19, 372/98, 372/100, 372/25
• US Class Current: 372/16
• CPC Class Codes: H01S 2301/085 solitons
• CPC Class Codes: H01S 3/08027 by a filter, e.g. a Fabry-Perot filter is used for wavelength setting
• CPC Class Codes: H01S 3/0811 incorporating a dispersive element, e.g. a prism for wavelength selection
• CPC Class Codes: H01S 3/0813 Configuration of resonator
• CPC Class Codes: H01S 3/094038 End pumping
• CPC Class Codes: H01S 3/105 by controlling the mutual position or the reflecting properties of the reflectors of the cavity , e.g. by controlling the cavity lengthH01S3/10076, H01S3/13 take precedence
• CPC Class Codes: H01S 3/1112 Passive mode locking
• CPC Class Codes: H01S 3/137 for stabilising of frequency
• CPC Class Codes: H01S 3/1625 titanium

Abstract

A process for operation of a laser device (1) is described, whereby circulating light pulses each comprising spectral components according to a plurality of longitudinal modes of a resonator configuration (3) are generated in the resonator configuration (3) and subjected to a compensation of group velocity dispersion, and a predetermined linear dispersion is introduced into the light path of the resonator configuration (3), so that at least one mode has a predetermined frequency and/or the mode distance between the modes has a predetermined value. Furthermore, regulations for stabilizing the laser device on the basis of this process and applications of the regulations for the generation for stabilized, ultra-short light pulses, generation of optical frequencies and in the frequency and/or time measuring technique as well as in the spectroscopy are described.

Claims

1. A process for the operation of a laser device having a resonator configuration with a light path, comprising the steps of:

generating light pulses circulating in the resonator configuration, said light pulses consisting of spectral components corresponding to multiple longitudinal modes of the resonator configuration;

compensating for the group velocity dispersion of said light pulses; and

inputting a predetermined linear dispersion into the light path of the resonator configuration, so that at least one mode possesses a predetermined frequency or the mode separation between the modes possesses a predetermined value;

said step of inputting a predetermined linear dispersion comprising at least one of a tilting of a transparent plane, a pushing in of a pair of prisms in the light path of the resonator configuration, a setting of the effective pumping power for the pumping of the active medium of the laser device, or a change of the geometric configuration of the laser device relative to a pump laser.

3. Process according to claim 1 or 2, in which the linear dispersion is introduced into the resonator configuration (3) within the framework of a mode control loop (I) dependent upon the frequency deviation of at least one first reference mode (M₁) of the light pulses from a reference frequency (f_ref), which is

the output frequency of an optical reference frequency generator (240),

a higher harmonic or an even number fraction of the output frequency or of the higher harmonic,

a frequency multiple of a lower frequency reference mode of the light pulses, or a fractional frequency of a higher frequency reference mode of the light pulses.

4. Process according to claim 3, whereby in the mode control loop (I) light pulse of the laser device (1) and light with the reference frequency (f_ref) are superposed and directed to a photosensitive element (211), whose electrical output signal shows a modulation at a beat frequency corresponding to the distance of the frequency of the first reference mode (M₁) from the reference frequency (f_ref), whereby a control (214) is provided, which sets the linear dispersion of the resonator configuration (3) so that the beat signal is minimal or possesses a predetermined beat frequency.

5. Process according to claim 4, whereby the optical reference frequency generator (240) is a stabilized continuous wave laser.

6. Process according to claim 3, whereby the optical reference frequency generator (240) is stabilized in a reference laser control loop (III) in relation to a second higher frequency reference mode (M₂) of the light pulses.

7. Process according to claim 1 or claim 2, whereby the liner dispersion is introduced into the resonator configuration (3) within the framework of a mode control loop (Ia, Ib) depending upon the deviation of the multiplied frequency of a first reference laser (240a), which is phase coupled with a first lower frequency reference mode (M₁) of the light pulses, from the frequency of a second reference laser (240b), which is phase coupled in a reference laser control loop (III) with a second higher frequency reference mode (M₂) of the light pulses.

8. Process according to claim 7 whereby the second reference laser (24 Gb) is phase coupled with the second higher frequency reference mode (M2) of the light pulses through a scaling stage.

9. Process according to claim 1 or 2, whereby the resonator length of the laser device (1) is regulated within the framework of a repetition frequency control loop (II), in which the repetition frequency (f_r) of the light pulses is superposed with a radio frequency derived from a radio frequency generator reference (25), whereby a control (224) is provided for, which sets the resonator length of the laser device (1) so that the oscillating signal formed by the superposition is minimal or possesses a predetermined beat frequency.

2. A process for the operation of a laser device having a resonator configuration with a light path, comprising the steps of:

generating light pulses circulating in the resonator configuration, said light pulses consisting of spectral components corresponding to multiple longitudinal modes of the resonator configuration;

compensating for the group velocity dispersion of said light pulses; and

inputting a predetermined linear dispersion into the light path of the resonator configuration, so that at least one mode possesses a predetermined frequency or the mode separation between the modes possesses a predetermined value;

said step of inputting a predetermined linear dispersion comprising changing a spectrally specific effective resonator length in a resonator branch, through which the light pulses traverse spectrally spatially separated after the compensation of the group velocity dispersion.

10. Process according to cliam 1 or claim 2 whereby the liner dispersion is introduced into the resonator configuration (3) within the framework of a repetition frequency control loop (II), in which the repetition frequency (f_r) of the light pulses is superposed with a radio frequency derived from a radio frequency reference generator (25), whereby a control (224) is provided for, which sets the resonator length of the laser device (1) so that the oscillating signal formed by the superposition is minimal or possesses a predetermined beat frequency.

11. Process according to claim 10, whereby the resonator length of the laser device (1) is regulated within the framework of a mode control loop (I) dependent upon the frequency deviation of at least a first s mode (M₁) of the light pulses from a reference frequency (f_ref), which is the output frequency of an optical reference frequency generator (24) or a higher harmonic or an even number fraction of the output frequency or the higher harmonic.

12. Process according to claim 10, whereby the resonator length of the laser device (1) is regulated within the framework of a mode control loop (I) dependent upon the frequency deviation of at least a first reference mode (M₁) of the light pulses from a reference frequency (f_ref), which is the output frequency of an optical reference frequency generator (24) or a higher harmonic or an even number fraction of the output frequency or the higher harmonic.

13. Process according to claim 10, whereby the resonator length of the laser device (1) is regulated within the framework of a mode control loop (I) dependent upon the frequency deviation of at least a first reference mode (M₁) of the light pulses from a reference frequency (f_ref), which is the output frequency of an optical reference frequency generator (24) or a higher harmonic or an even number fraction of the output frequency or the higher harmonic.

14. Application of a process or a laser device according to claim 2 for the measurement of optical frequencies of frequency differential generation of optical frequencies, bridging of large frequency differences in optical division chains, generation of optical transmitting frequencies in telecommunications technology, spectroscopic measurement of atomic electronic transitions, or the bridging of the frequency of an optical frequency normal to a measuring frequency that may be counted with electronic means.

15. A laser device for production of short light pulses, having a resonator configuration with

an active medium;

a resonator formed with an optical fiber or with a plurality of mirrors, including an incoupling mirror for the coupling in of pump light to the active medium and two or more tilted mirrors for directing resonating light to an outcoupling mirror for the output of light pulses;

a compensating mechanism for the compensation of the group velocity dispersion of the light pulses;

a dispersion setting device for the input of a predetermined linear dispersion into the light path of the resonator configuration; and

said dispersion setting device comprising at least one of a transparent plate with a tilting mechanism, a pair of prisms with a sliding mechanism, which are included in the resonator configuration, an apparatus for the variation of the effective pump power of a pump laser, or an apparatus for the variation of the geometrical configuration of the laser device relative to the pump laser.

17. Laser device according to claim 15 or claim 16, which is constructed as a ring laser.

18. Laser device according to claim 17, whereby a resonator length setting device (5) is provided for the change of the resonator length through a change in positioning of one of the tilted minors (33b).

19. Laser device according to claims 15, 16 or 18 whereby a mode control loop (I, 210, 214) is provided for the regulation of the dispersion setting device (7, 8, 8′

) or the regulation of the resonator length setting device (5), dependent upon the frequency deviation of at least one frequency component of the light pulse from a reference frequency (f_ref), which is the output frequency of an optical reference frequency generator (240) or a higher harmonic or an even number fraction of the output frequency or of the higher harmonic or a multiplied frequency of a lower frequency reference mode or a divided frequency of a higher frequency reference mode of the light pulses.

20. Laser device according to claim 19, whereby the mode control loop (I, 210, 214) includes an apparatus (211) for the production of a beat signal from the frequency component of the light pulses and the reference frequency (f_ref) and a mode control (214) for the dispersion setting device (7) or the resonator length setting device (5), so that the dispersion setting device (7) or the resonator length setting device (5) is activated in such a way that the beat signal is either minimal or possesses a predetermined beat frequency.

21. Laser device according to claim 19, whereby the mode control loop (I, 210, 214) includes an apparatus (211) for the production of a beat signal from the frequency component of the light pulses and the reference frequency (f_ref) and a mode control (214) for the dispersion setting device (7) or the resonator length setting device (5), so that the dispersion setting device (7) or the resonator length setting device (5) is activated in such away that the beat signal is either minimal or possesses a predetermined beat frequency.

22. Laser device according to claim 21, whereby a filter element (212) for spectral selective detection of the light pulses is provided at the photosensitive element.

23. Laser device according to claim 19, whereby further a reference laser control loop (III, 231) is provided for the regulation of the optical reference frequency generator or reference laser (240), with a device (231) for the generation of a beat signal from a higher frequency component of the light pulses or a part of tis frequency component and a frequency equal to a multiple of the reference frequency (f_ref), and a setting device for the setting of the optical reference frequency generator or reference laser (240) so that the beat signal is minimal or has a predetermined beat frequency.

24. Laser device according to claim 15, claim 16 or claim 18 whereby a mode control loop (I, 210, 214) is provided for the relegation of the dispersion setting device (7, 8, 8′

) or the regulation of the resonator length setting device (5), dependent upon the frequency deviation of the frequency of a first reference laser (240a), which is phase coupled with a first lower frequency reference mode (M₁) of the light pulses, from the frequency of a second reference laser (240b), which is phase coupled wit a second (M₂) higher frequency reference mode of the light pulses.

25. Laser device according to claim 15 or 16 whereby a repetition frequency control loop (II, 220, 224) is provided for the regulation of the resonator length setting device (5) or the dispersion setting device (7, 8, 8′

), dependent upon the frequency deviation of at least one differential frequency between the repetition frequency of the light pulses and a radio frequency.

26. Laser device according to claim 25, whereby a radio frequency reference generator (25) is provided for the generation of the reference radio frequency and the repetition frequency control loop comprise a device for the generation of a beat signal from the signal of a photosensitive element (221) that captures the light pulses, and from the signal of a radio frequency reference generator (250), and a frequency reference control (224) for the resonator length setting device (5) or the dispersion setting device (7, 8, 8′

), whereby the repetition frequency control (224) is structured so that the resonator length setting device or the dispersion setting device (7, 8, 8′

) is operated so that the second oscillating signal is minimal or possesses a predetermined frequency.

27. Laser device according to claim 15 or 16, whereby the active medium (4) includes a solid or a dye medium.

28. Laser device according to claim 15 or 16, whereby a device (201) is provided for self phase modulation.

16. A laser device for production of short light pulses, having a resonator configuration with

an active medium;

a resonator formed with an optical fiber or with a plurality of mirrors, including an incoupling mirror for the coupling in of pump light to the active medium and two or more tilted mirrors for directing resonating light to an outcoupling mirror for the output of light pulses;

a compensating mechanism for the compensation of the group velocity dispersion of the light pulses;

a dispersion setting device for the input of a predetermined linear dispersion into the light path of the resonator configuration; and

said dispersion setting device comprising a pivoting mechanism on a tilted mirror functioning as a resonator end mirror and being located in a branch of the resonator on the side of the compensating mechanism facing away from the active medium.