Repetitively Q-switched laser pumped by laer diodes and Q-switched with an intracavity variable speed moving aperture

• US 5,528,611 A
• Filed: 02/16/1995
• Issued: 06/18/1996
• Est. Priority Date: 02/16/1995
• Status: Expired due to Fees

• Current Assignee: the united states of america as represented by the secretary of the navy
• Original Assignee: the united states of america as represented by the secretary of the navy
• Inventors: Scheps, Richard
• Primary Examiner(s): Scott, Jr., Leon
• Application Number:
  US08/389,463
• Time in Patent Office: 488 Days
• Field of Search: 372/92, 372/98, 372/99, 372/103, 372/9, 372/14, 372/15, 372/66
• US Class Current: 372/14
• CPC Class Codes: H01S 3/094038 End pumping
• CPC Class Codes: H01S 3/09415 the pumping beam being parallel to the lasing mode of the pumped medium, e.g. end-pumping
• CPC Class Codes: H01S 3/1022 by controlling the optical pumping
• CPC Class Codes: H01S 3/121 using intracavity mechanical devices

Abstract

A laser is end pumped by laser diodes and is repetitively Q-switched using an intracavity variable speed moving aperture. The aperture apparatus includes a precision motor which drives a pair of matched aperture blades and produces efficient Q-switched operation over a wide range of output powers and repetition rates. Each aperture blade may contain an identical number of transmissive and opaque regions, and two aperture blades may be mounted onto the motor in a manner that allows continuous adjustment of the aperture width. In a preferred embodiment the aperture blades are shaped as circular discs. The laser resonator mode is nearly hemispherical, and the aperture blade is located at or near the laser resonator mode waist. When pumped with the optimum pump flux, efficient repetitively Q-switched operation is obtained as long as the Q-switch opening time is shorter than the pulse build-up time. The pulse build-up time can be calculated, and the Q-switch opening time is defined in accordance with this inventive concept. The Q-switch opening time is a function of the laser resonator mode diameter at the location of the aperture blade and the velocity of the aperture blade as it moves through the resonator mode. The Q-switch opening time is a fraction of the time required for the edge of the aperture blade to traverse the entire resonator mode diameter.

Claims

1. A laser for providing Q-switched emission comprising:

a laser resonator having a laser resonator cavity, said laser resonator including a highly reflective end element, a laser gain element, and an output coupler reflective element arranged to produce a nearly hemispherical laser resonator mode of energy having a laser resonator mode waist;

a laser diode producing optical emission for optically exciting said laser gain element to emit laser emission, said optical emission being focused to produce a pump mode waist that occupies a common region with said laser resonator mode waist; and

an aperture apparatus having an aperture blade disposed in said laser resonator cavity near said laser resonator mode waist for interrupting laser resonator oscillation, said aperture blade having a transmissive portion and a portion opaque for said laser emission and being positioned for producing Q-switched emission.

2. The laser of claim 1 in which said pump mode waist is substantially mode-matched to said laser resonator mode waist.

3. The laser of claim 1 in which said optical emission end pumps said laser gain element.

4. The laser of claim 1 in which said aperture apparatus produces single shot Q-switched emission.

5. The laser of claim 1 in which said aperture apparatus produces repetitive Q-switched emission.

6. The laser of claim 1 in which said laser diode produces a continuous optical emission.

7. The laser of claim 1 in which said laser diode produces a pulsed optical emission at a repetition frequency between 20 Hz and 5,000 Hz.

8. The laser of claim 1 in which said laser diode produces a pulsed optical emission that has a pulse duration of less than twice the fluorescence lifetime of dopant ions in said laser gain element, and said pulsed optical emission terminates at approximately the time of the emission of a Q-switched pulse by said laser.

9. The laser of claim 1 in which said laser gain element comprises a Nd:

YAG laser gain element.

10. The laser of claim 1 in which said laser gain element contains a doping concentration of approximately 1.1% Nd³⁺ ions.

11. The laser of claim 1 in which said laser gain element contains Cr³⁺ ions.

12. The laser of claim 1 in which said laser diode comprises at least one AlGaAs laser diode.

13. The laser of claim 1 in which said laser diode comprises at least one AlGaInP laser diode.

14. The laser of claim 1 in which said aperture apparatus comprises:

a variable speed motor having a rotation rate between 0 Hz and approximately 100 Hz, and

a first aperture blade connected to said variable speed motor having at least one aperture.

15. The laser of claim 14 further including:

a second aperture blade connected to said variable speed motor for producing a variable aperture width when either aperture blade is rotated with respect to the other.

16. The aperture apparatus of claim 15 in which each of said first and said second aperture blades contain a plurality of apertures.

17. The aperture apparatus of claim 14 in which said first aperture blade and said second aperture blade are flat.

18. The aperture blade of claim 1 in which said transmissive portion transmits said optical emission and said laser emission, and said opaque portion transmits said optical emission and absorbs said laser emission.

19. A method for Q-switching a laser comprising the steps of:

providing a laser resonator including an output coupler reflective element, a highly reflective end element, and a laser gain element, disposed to produce a laser resonator mode of energy having a laser resonator mode waist;

pumping said laser gain element with optical emission from a laser diode focused to a pump mode waist that occupies a common region with said laser resonator mode waist to produce laser emission from said laser gain element; and

placing an aperture apparatus having an aperture blade near said laser resonator mode waist, said aperture blade being positioned to interrupt laser resonator oscillation for producing Q-switched emission.

20. The method of claim 19 in which said step of providing comprises the step of producing a nearly hemispherical laser resonator mode of energy having said laser resonator mode waist.

21. The method of claim 19 in which said step of pumping comprises the step of end pumping said laser gain element.

22. The method of claim 19 in which said step of pumping comprises the step of substantially mode matching said pump mode waist to said laser resonator mode waist.

23. The method of claim 19 in which said step of placing comprises the step of producing single shot Q-switched emission.

24. The method of claim 19 in which said step of placing comprises the step of producing repetitive Q-switched emission.

25. A method according to claim 19 further comprising the step of:

optimizing the power of said optical emission to produce an optimum pump power determined by the factors of laser resonator gain and loss, and output mirror reflectivity.

26. A method according to claim 19 further comprising the steps of:

providing a plurality of apertures in said aperture blade to assure a predetermined Q-switching repetition rate; and

rotating said aperture blade at a rate to assure that the Q-switch opening time is less than the pulse build-up time of the Q-switched pulse.

27. A method according to claim 19 further comprising the step of:

adjusting parameters of said laser to assure that the Q-switch opening time is less than the pulse build-up time of the Q-switched pulse.

28. The method of claim 19 in which said step of pumping comprises the step of generating a CW optical emission.

29. The method of claim 19 in which said step of pumping comprises the step of providing a pulsed optical emission having a pulse duration less than twice the fluorescence lifetime of dopant ions in said laser gain element, said pulsed optical emission terminating when a Q-switched pulse is emitted.

30. A laser for providing Q-switched emission comprising:

a laser resonator having a laser resonator cavity including a laser gain element producing a laser resonator mode of energy having a laser resonator mode waist;

a source of light exciting said laser gain element in an end pumping mode to emit laser emission, said light being focused to produce a pump mode waist that occupies a common region with said laser resonator mode waist; and

an aperture apparatus having an aperture blade disposed in said laser resonator cavity for interrupting laser resonator oscillation, said aperture blade having a portion transmissive and a portion opaque for said laser emission.

31. A laser for providing Q-switched emission comprising:

a laser resonator having a laser resonator cavity including a laser gain element, said laser resonator producing a laser resonator mode of energy having a laser resonator mode waist;

a source of light exciting said laser gain element to emit laser emission; and

an aperture apparatus having an aperture blade disposed in said laser resonator cavity near said laser resonator mode waist for interrupting laser resonator oscillation, said aperture blade having a portion transmissive and a portion opaque for said laser emission.

32. The laser of claim 31 in which said optical emission end pumps said laser gain element.