Ruby laser pumped ultrashort pulse laser

Abstract

An apparatus and method are provided for producing an ultrashort pulsed output beam. A 694 nm pump beam from a first GaN semiconductor laser diode pumped, Q-switched ruby laser is directed into at least one amplifier that includes a broadband gain element doped with trivalent chromium ions (Cr.sup.3+). A spectrally linearly chirped low-intensity seed pulse from a master oscillator is directed into the at least one optically pumped amplifier to produce an amplified linear chirped pulsed output beam. A 694 nm second pump beam from a second GaN semiconductor laser diode pumped, Q-switched ruby laser is directed into a power amplifier that also includes a broadband gain element doped with trivalent chromium ions (Cr.sup.3+). The amplified linear chirped pulsed output beam is directed into the optically pumped power amplifier to produce a high energy linear chirped pulsed output beam which is then directed into a pulse compressor to produce the ultrashort pulsed output beam.

Claims

1. An apparatus, comprising: a master oscillator configured to provide a spectrally linearly chirped low-intensity seed pulse; one or more preamplifiers, wherein each preamplifier of said one or more preamplifiers comprises a first broadband gain element doped with trivalent chromium ions (Cr.sup.3+); one or more GaN semiconductor laser diode pumped, Q-switched ruby lasers, wherein each ruby laser of said ruby lasers is configured to provide a 694 nm preamplifier pump beam; means for producing one or more optically pumped preamplifiers by directing each said 694 nm preamplifier pump beam into its own preamplifier of said one or more preamplifiers; means for directing said seed pulse through each optically pumped preamplifier of said one or more optically pumped preamplifiers to produce an amplified linear chirped pulsed output beam; a power amplifier comprising a second broadband gain element doped with trivalent chromium ions (Cr.sup.3+); a last GaN semiconductor laser diode pumped, Q-switched ruby laser configured to provide a 694 nm last pump beam; means for directing said last pump beam into said power amplifier to produce an optically pumped power amplifier; a pulse compressor; and means for directing said amplified linear chirped pulsed output beam into said pulse compressor to produce a time compressed ultrashort pulsed output beam.

2. The apparatus of claim 1, wherein said first broadband gain element and said second broadband gain element are doped with trivalent chromium ions (Cr.sup.3+) selected from the group consisting of Cr.sup.3+:ZnWO.sub.4, Cr.sup.3+:Sc.sub.2(WO.sub.4).sub.2, Cr.sup.3+:Al.sub.2(WO.sub.4).sub.2, Cr.sup.3+:GSGG, Cr.sup.3+:MgO, Cr.sup.3+:LiSAF, and Cr.sup.3+:phosphate glass.

3. A method, comprising: producing one or more optically pumped preamplifiers by directing a 694 nm preamplifier pump beam from one or more GaN semiconductor laser diode pumped, Q-switched ruby lasers into its own preamplifier of one or more preamplifiers comprising a first broadband gain element doped with trivalent chromium ions (Cr.sup.3+); directing a spectrally linearly chirped low-intensity seed pulse from a master oscillator through each optically pumped preamplifier of said one or more optically pumped preamplifiers to produce an amplified linear chirped pulsed output beam; directing a last pump beam into a power amplifier comprising a second broadband gain element doped with trivalent chromium ions (Cr.sup.3+) to produce an optically pumped power amplifier, wherein said last pump beam is produced by a last GaN semiconductor laser diode pumped, Q-switched ruby laser configured to provide a 694 nm last pump beam; directing said amplified linear chirped pulsed output beam into said optically pumped power amplifier to produce a last linear chirped pulsed output beam; and directing said last linear chirped pulsed output beam into a pulse compressor to produce a time compressed ultrashort pulsed output beam.

4. The method of claim 3, wherein said first broadband gain element and said second broadband gain element are doped with trivalent chromium ions (Cr.sup.3+) selected from the group consisting of Cr.sup.3+:ZnWO.sub.4, Cr.sup.3+:Sc.sub.2(WO.sub.4).sub.2, Cr.sup.3+:Al.sub.2(WO.sub.4).sub.2, Cr.sup.3+:GSGG, Cr.sup.3+:MgO, Cr.sup.3+:LiSAF, and Cr.sup.3+:phosphate glass.

5. An apparatus, comprising: a master oscillator configured to provide a spectrally linearly chirped low-intensity seed pulse; a preamplifier comprising a first broadband gain element doped with trivalent chromium ions (Cr.sup.3+); a GaN semiconductor laser diode pumped, Q-switched ruby laser configured to provide a 694 nm preamplifier pump beam; means for directing said 694 nm preamplifier pump beam into said preamplifier to produce an optically pumped preamplifier; means for directing said seed pulse through said preamplifier to produce an amplified linear chirped pulsed output beam; a power amplifier comprising a second broadband gain element doped with trivalent chromium ions (Cr.sup.3+); a last GaN semiconductor laser diode pumped, Q-switched ruby laser configured to provide a 694 nm last pump beam; means for directing said last pump beam into said power amplifier to produce an optically pumped power amplifier; a pulse compressor; and means for directing said amplified linear chirped pulsed output beam into said pulse compressor to produce a time compressed ultrashort pulsed output beam.

6. The apparatus of claim 5, wherein said first broadband gain element and said second broadband gain element are doped with trivalent chromium ions (Cr.sup.3+) selected from the group consisting of Cr.sup.3+:ZnWO.sub.4, Cr.sup.3+:Sc.sub.2(WO.sub.4).sub.2, Cr.sup.3+:Al.sub.2(WO.sub.4).sub.2, Cr.sup.3+:GSGG, Cr.sup.3+:MgO, Cr.sup.3+:LiSAF, and Cr.sup.3+:phosphate glass.

7. A method, comprising: directing a 694 nm preamplifier pump beam from a GaN semiconductor laser diode pumped, Q-switched ruby lasers into a preamplifier comprising a first broadband gain element doped with trivalent chromium ions (Cr.sup.3+) to produce an optically pumped preamplifier, directing a spectrally linearly chirped low-intensity seed pulse from a master oscillator through said optically pumped preamplifier to produce an amplified linear chirped pulsed output beam; directing a last pump beam into a power amplifier comprising a second broadband gain element doped with trivalent chromium ions (Cr.sup.3+) to produce an optically pumped power amplifier, wherein said last pump beam is produced by a last GaN semiconductor laser diode pumped, Q-switched ruby laser configured to provide a 694 nm last pump beam; directing said amplified linear chirped pulsed output beam into said optically pumped power amplifier to produce a last linear chirped pulsed output beam; and directing said last linear chirped pulsed output beam into a pulse compressor to produce a time compressed ultrashort pulsed output beam.

8. The method of claim 7, wherein said first broadband gain element and said second broadband gain element are doped with trivalent chromium ions (Cr.sup.3+) selected from the group consisting of Cr.sup.3+:ZnWO.sub.4, Cr.sup.3+:Sc.sub.2(WO.sub.4).sub.2, Cr.sup.3+:Al.sub.2(WO.sub.4).sub.2, Cr.sup.3+:GSGG, Cr.sup.3+:MgO, Cr.sup.3+:LiSAF, and Cr.sup.3+:phosphate glass.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) The accompanying drawings, which are incorporated into and form a part of the disclosure, illustrate embodiments of the invention and, together with the description, serve to explain the principles of the invention.

(2) FIG. 1 is a block diagram of a prior art Ti:sapphire (TiS) based ultrashort pulse CPA-compressor laser, comprised of two main subsystems.

(3) FIG. 2 is a block diagram of an ultrashort pulse CPA-compressor laser of the present invention, comprising a pump pulse subsystem based on GaN pumped ruby, and an ultrashort pulse CPA-compressor subsystem based on a chromium (Cr.sup.3+) doped broadband gain medium.

(4) FIG. 3 is a more detailed block diagram of an ultrashort pulse CPA-compressor subsystem based on a chromium (Cr.sup.3+) doped broadband gain medium that is directly pumped by one or more GaN laser diode pumped, Q-switched ruby lasers.

(5) FIG. 4 shows plots of room temperature absorption and emission spectra of a Cr.sup.3+:ZnWO.sub.4 crystal.

(6) FIG. 5 is a comparison of key laser spectroscopic properties of Ti:Al.sub.2O.sub.3, Cr.sup.3+ doped crystals: ZnWO.sub.4, Al.sub.2(WO.sub.4).sub.3, Cr.sup.3+:Sc.sub.2(WO.sub.4).sub.3, GSGG, MgO, and LiSAF.

DETAILED DESCRIPTION OF THE INVENTION

(7) FIG. 2 shows a block diagram of the ultrashort pulse CPA-compressor laser of the present invention. This laser system comprises two major subsystems: a Q-switched, 694 nm ruby pump pulse subsystem 25, and an ultrashort pulse CPA-compressor subsystem 28.

(8) Subsystem 25 comprises a pump GaN laser diode (or diode array) 21 emitting an output beam 22 at a wavelength near 405 nm, and a Q-switched ruby laser 23 that generates a Q-switched output beam 24 at a wavelength of 694 nm, with characteristic pulse durations in the multi-tens of nanoseconds regime. Output beam 24 is used in turn to pump broadband chromium (Cr.sup.3+) doped crystal (or crystals) 26 contained within a chirp pulse amplifier (CPA)-compressor type system 28, to produce ultrashort pulse output beam 27. Chirped pulse amplifier and compressor systems are known in the art. See, e.g., U.S. Pat. No. 8,780,440, titled Dispersion Compensation in Chirped Pulse Amplification Systems, filed May 18, 2010, issued Jul. 15, 2014, incorporated herein by reference.

(9) FIG. 3 shows in more detail a block diagram of the CPA-compressor subsystem 39 of the present invention. It comprises 1) a master oscillator (MO) 31 that provides a spectrally linearly chirped, low-intensity seed pulse 32; 2) a sequence of preamplifiers 33 containing broadband Cr.sup.3+ doped gain elements that produce amplified linear chirped pulse output beam 34; 3) power amplifier stage 35 containing a broadband Cr.sup.3+ doped gain element that produces high energy linear chirp pulse output beam 36; and 4) pulse compressor stage 37 that removes the linear chirp and produces time compressed ultrashort pulse output beam 38. Preamplifiers 33 are optically pumped by Q-switched output beam 24 from subsystem 25 of FIG. 2. Power amplifier 35 is optically pumped by Q-switched output beam 24 from subsystem 25. Subsystem 25 and subsystem 25 are identical in type, but appropriately scaled in energy. Q-switched output beam 24 is identical in type to Q-switched output beam 24 but are also scaled in energy.

(10) At least several broadband gain media manifest laser spectroscopic and physical properties useful in the present invention, including but not limited to the following Cr.sup.3+ doped crystals: ZnWO.sub.4; Al.sub.2(WO.sub.4).sub.3; Sc.sub.2(WO.sub.4).sub.3, MgO, GSGG, LiSAF, and Cr.sup.3+:phosphate glass. For example, FIG. 4 shows the polarized, absorption and emission spectra of Cr.sup.3+:ZnWO.sub.4 crystal at room temperature. Two broad pump bands lie at wavelengths shorter than about 900 nm, and a spectrally broad emission band lies at a wavelength longer than about 900 nm, peaked at a wavelength of about 1000 nm. This crystal manifests a strong, relatively broad absorption feature at 694 nm, matching the 694 nm output wavelength of the GaN pumped ruby Q-switched subsystem. This crystal also manifests a broadband emission peaked at 1000 nm, suitably broad to support the generation of sub-100 fsec pulses. The fluorescence lifetime of this emission is 5.4 microsecond, and is suitably long to permit effective, practical multi-pass/regen amplification. Broadband laser gain and laser emission at a wavelength of 1000 nm has been observed in a Cr.sup.3+:ZnWO.sub.4 laser.

(11) The key laser spectroscopic parameters of Cr.sup.3+ doped crystals ZnWO.sub.4, Al.sub.2(WO.sub.4).sub.3, Sc.sub.2(WO.sub.4).sub.3, GSGG, MgO, and LiSAF are shown in FIG. 5, in comparison with those of Ti.sup.3+:Al.sub.2O.sub.3 (TiS). These data indicate that all of the listed Cr.sup.3+ doped crystals meet the criteria for effective use in the present invention.

(12) Inspection of the spectroscopic literature reveals that certain Cr.sup.3+ doped glasses offer spectroscopic characteristics quite similar to those listed in FIG. 5, and therefore can be considered as suitable for use in the present invention.

(13) The foregoing description of the invention has been presented for purposes of illustration and description and is not intended to be exhaustive or to limit the invention to the precise form disclosed. Many modifications and variations are possible in light of the above teaching. For example, coupling optics may be used to direct a beam from one element to another, or a beam source may be pointed directly at a second element without intervening optics. These and other known beam directing techniques are considered herein to be means for directing. The embodiments disclosed were meant only to explain the principles of the invention and its practical application to thereby enable others skilled in the art to best use the invention in various embodiments and with various modifications suited to the particular use contemplated. The scope of the invention is to be defined by the following claims.