CO2 Laser

Abstract

Efficient laser diode excited Thulium (Tm) doped solid state systems, directly matched to a combination band pump transition of Carbon Dioxide (CO.sub.2), have matured to the point that utilization of such in combination with CO.sub.2 admits effectively a laser diode pumped CO.sub.2 laser. The laser diode excited Tm solid state pump permits Continuous Wave (CW) or pulsed energy application. Appropriate optical pumping admits catalyzer free near indefinite gas lifetime courtesy of the absence of significant discharge driven dissociation and contamination. As a direct consequence of the preceding arbitrary multi isotopologue CO.sub.2, symmetric and asymmetric, gas mixes may be utilized without significant degradation or departure from initial mix specifications. This would admit, at raised pressure, a system continuously tunable from 9 m to 1.5 m, or sub picosecond amplification. This methodology offers advantages in regards scalability, pulse energy and power over alternative non linear conversion techniques in access to this spectral region.

Claims

1. An optically pumped CO.sub.2 laser comprising, at least, a laser diode excited Tm solid state laser tuned to the 00.sup.00.fwdarw.20.sup.01 combination band transition(s) of the CO.sub.2 isotopologue(s) to be optically pumped for lasing purposes; gas cell with desired CO.sub.2 gas mix and pressure internal to a resonant cavity if required and pump field and CO.sub.2 cavity axis combination methodology; CO.sub.2 laser in atmospherically transmissive window within spectral region from 9 m to 11.5 m.

2. An optically pumped CO.sub.2 laser, according to claim 1, wherein if the optically pumped CO.sub.2 is at pressure, laser diode pumped solid state system efficiency is not limited by molecular line widths and more relaxed conditions apply; at reduced pressure where molecular lines resolve individually multiple rotational vibrational transitions may be pumped thus broadening solid state system interaction bandwidth sufficiently for efficient extraction, achievable with single or multi isotopologue gas mix.

3. An optically pumped CO.sub.2 laser, according to claim 1, wherein the optically pumped CO.sub.2 metastable levels accessible for defined 9 m to 11.5 m lasing include the 00.sup.01 and 01.sup.11 levels.

4. An optically pumped CO.sub.2 laser, according to claim 1, wherein the Tm solid state pump laser may be CW or pulsed and thus the optically pumped CO.sub.2 lasing may be CW or pulsed.

5. An optically pumped CO.sub.2 laser, according to claim 1, wherein the CO.sub.2 component is optically pumped and thus, above atmosphere to significantly above atmosphere operation is straightforward other than for pressure containment considerations.

6. An optically pumped CO.sub.2 laser, according to claim 1, wherein the CO.sub.2 component admits utilization of atmospheric, or higher, pressure non pumped low gain gas cells intra cavity to suppress 4.2 m to 4.3 m and 15.26 m transitions if desired or required.

7. An optically pumped CO.sub.2 laser, according to claim 1, wherein the CO.sub.2 component, which absent dissociation and discharge related gas contamination under appropriate optical pump conditions, results in near indefinite gas lifetimes.

8. An optically pumped CO.sub.2 laser, according to claim 1, wherein in the absence of dissociation a catalyzer is not a system requirement.

9. An optically pumped CO.sub.2 laser, according to claim 1, wherein given a laser diode excited Tm solid state pump, then fact that ceramic Tm:YAG has been formed and thus in principle arbitrarily large and shaped Tm:YAG structures can be fabricated in conjunction with a demonstrated 4 kJ/liter extraction, coupled with the inherent volume scalability of the optically pumped gas component allows for high energy pulsed applications with output in the 9 m to 11.5 m band; YAG is referenced, but any other suitable solid state host is acceptable.

10. An optically pumped CO.sub.2 laser, according to claim 1, wherein the CO.sub.2 component isotopologue(s) may be admixed with one, or more buffer gases selected from the group consisting of Helium, Argon and Nitrogen.

11. An optically pumped CO.sub.2 laser, according to claim 1, wherein the laser diode excited Tm doped solid state optically pumped molecular CO2 approach is absent chemical reaction sourced optical pumping, and thus is absent related precursor or product gas handling issues plus any efficiency shortfall attributable to line mismatches

12. An optically pumped CO.sub.2 laser comprising sustained and preserved multi-CO.sub.2 isotopologue, symmetric and asymmetric, mix capability courtesy of absence of significant optical pump driven dissociation under appropriate conditions.

13. An optically pumped CO.sub.2 laser according to claim 12, wherein the CO.sub.2 component, which absent dissociation, admits utilization of an arbitrarily proportioned multi isotopologue CO.sub.2 gas mix offering optimal line tunability from 9 m through 11.5 m at moderate pressure and continuous tunability from 9 m through 11.5 m at high pressure.

14. An optically pumped CO.sub.2 laser, according to claim 12, wherein the CO.sub.2 component admits utilization of atmospheric, or higher, pressure non pumped low gain gas cells intra cavity to suppress 4.2 m to 4.3 m and 15.26 m transitions if desired or required.

15. An optically pumped CO.sub.2 laser, according to claim 12, wherein given spectral tunability a system well suited to remote sensing of agents of interest is enabled.

16. An optically pumped CO.sub.2 laser, according to claim 12, wherein at pressure a system is enabled which is suitable for use for short pulse amplification of 10 m CO.sub.2 laser events into the sub picosecond timescale (FIG. 3), or for compact high energy pulsed extraction.

17. An optically pumped CO.sub.2 laser, according to claim 12, wherein as a result of the feasibility of utilization of asymmetric isotopologues and/or the 01.sup.11 excited level the system pressure required for continuous tunability will be 50% or less than that required for the purely symmetric isotopologues.

18. An optically pumped CO.sub.2 laser, according to claim 12, wherein absent dissociation, a catalyzer is not a system requirement.

19. An optically pumped CO.sub.2 laser comprising a laser diode excited Tm doped solid state optical pump wherein the approach to CO.sub.2 is absent the high voltage switching, discharge electrode erosion and EMI issues of traditional pulse discharge (significantly gain switched) CO.sub.2 lasers.

20. An optically pumped CO.sub.2 laser, according to claim 19, wherein absent high voltage high energy switching and high discharge current related electrode erosion, system mean time between required services will be extended.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0027] 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.

[0028] FIG. 1: Is an illustration of the pulsed manifestation of the invention. One or more synchronized pulsed oscillators, individually tuned and locked onto selected CO.sub.2 isotopologue(s) pump transitions (00.sup.00.fwdarw.20.sup.01) (A). Output via spectral beam combiner (B) (or any other beam combiner if required) into amplifier (C). Amplifier output via spectral beam combiner (or dichroic optics) to admit introduction to CO.sub.2 laser cavity (D) with 10 m output (E).

[0029] FIG. 2: Is an illustration of the CW manifestation of the invention. One or more CW or synchronized quasi CW fiber oscillators, tuned and locked individually to selected CO.sub.2 isotopologue(s) pump transitions (00.sup.00.fwdarw.20.sup.01) (A). Output via suitable beam combiner (B) into fiber amplifier (C). Amplifier output, via suitable beam combiner or dichroic optics, into CO.sub.2 laser cavity (D) with 10 m output (E).

[0030] FIG. 3: Is an example of an induced multi-isotopologue gain spectrum at 5 atms for an arbitrary pre-mix. This, excluding transition contributions from the anticipated 01.sup.11 metastable level which would serve to smooth and further broaden the gain spectrum.

DETAILED DESCRIPTION OF INVENTION

[0031] Laser diode excited Thulium (Tm) doped solid state system component (FIG. 1. A, B, C & FIG. 2. A, B, C). Both pulsed and continuous wave (CW) operation is feasible. In pulsed case extractions of 4 kJ/liter is achievable, enabling a compact related system. Ceramic host structures have been formed, admitting arbitrary shaping and sizing of Tm:host (host being any suitable glass or crystalline host) and thus energy/power scaling. Operation is quasi 4 level, thus pulsed efficiency, optical out to optical absorbed, in excess of 40% is in principle achievable. In CW case, slope efficiencies approaching 80% is feasible, with single frequency operation at 1 kW, without any indication of onset of stimulated Brillouin scattering limiting. Tuning spectral range can extend from 1.74 m to 2.017 m. The CO.sub.2 00.sup.00.fwdarw.20.sup.01 pump transitions for the isotopologues .sup.12C.sup.16O.sub.2, .sup.13C.sup.16O.sub.2, .sup.12C.sup.18O.sub.2, .sup.13C.sup.18O.sub.2, .sup.16O.sup.12C.sup.18O and .sup.16O.sup.13C.sup.18O are found to spectrally range from 1.949 m to 2.035 m. There is thus significant overlap and hence pump access.

[0032] The laser diode excited Tm doped solid state optical pump approach to CO.sub.2 is absent the high voltage switching, discharge electrode erosion and electromagnetic interference (EMI) issues of traditional pulse discharge, significantly gain switched, CO.sub.2 lasers. In addition, it can readily access the high pressure CO.sub.2 operational regime desirable in certain applications.

[0033] There are a variety of photonic and collisionally mediated interactions which have the capability of rapidly transitioning population from the pump terminal level to either, or both, the 00.sup.01 and 01.sup.11 metastable lasing levels. The 01.sup.11 level presents with a strong Q branch transition (15.3 m) to the 00.sup.01 level should such be desirable. This may, by design be encouraged or discouraged. The non-zero angular momentum metastable level is desirable for specific applications as it presents with twice the transition lines of the zero angular momentum case and thus will be continuously tunable at a pressure below that required for zero angular momentum metastable level.

[0034] Optical pumping, absent the significant dissociation and catalyzer driven recombination as required in most competitive discharge pumped CO.sub.2 systems, admits arbitrary sustainable use of predetermined CO.sub.2 isotopologue mixes. For example, in a discharge driven system with catalyzer one can use a mix of .sup.12C.sup.16O.sub.2+.sup.13C.sup.16O.sub.2, but not of .sup.12C.sup.16O.sub.2+.sup.12C.sup.18O.sub.2 or .sup.12C.sup.16O.sub.2+.sup.13C.sup.18O.sub.2, as mixture will in time corrupt to .sup.12C.sup.16O.sub.2+.sup.12C.sup.18O.sub.2+.sup.18O.sup.12C.sup.16O and .sup.12C.sup.16O.sub.2+.sup.13C.sup.18O.sub.2+.sup.18C.sup.12C.sup.16O+.sup.18O.sup.13C.sup.16O. In the case of appropriate optical pumping, as indicated, a desirable arbitrary premix of these gases can be implemented and will be largely preserved in use.

[0035] Continuous tunability deriving from an appropriate gas premix, pressure and optical pumping is expected for example then to present with a sustainable gain spectral distribution of the form FIG. 3.

[0036] The following is a description of the best mode contemplated by the inventor of the laser diode excited solid state optically pumped CO.sub.2 system. A laser diode excited Tm solid state pulsed laser, frequency(s) locked on desired CO.sub.2 isotopologue(s) combination band(s) (00.sup.00.fwdarw.20.sup.01) (FIG. 1. A, B, C), seed oscillators synchronized, output coupled as input into CO.sub.2 cavity region and mode matched to related CO.sub.2 cavity determined lasing volume (FIG. 1. D). Laser plus amplifier combination possibly amplifying more than one pump transition frequency as indicated in FIG. 1 A, B, C.

[0037] The following is a description of an alternate embodiment contemplated by the inventor of the laser diode excited solid state optically pumped CO.sub.2 system. A laser diode excited Tm solid state CW laser, frequency(s) locked on desired CO.sub.2 isotopologue(s) combination band(s) (00.sup.00.fwdarw.20.sup.01) (FIG. 2. A, B, C), output coupled as input into CO.sub.2 cavity region and mode matched to related CO.sub.2 cavity determined lasing volume (FIG. 2. D). Laser plus amplifier combination possibly amplifying more than one pump transition frequency as indicated in FIG. 2. A, B, C.

[0038] At high pressure, 00.sup.00.fwdarw.20.sup.01 pump transition bandwidth is sufficiently large to admit sufficiently broad solid state system bandwidth for efficient operation. At reduced pressure and for pump events under several hundred nanoseconds, for a single CO.sub.2 isotopologue pumped on several selected rotational vibrational lines of the 00.sup.00.fwdarw.20.sup.01 transition, the interaction will yield adequate solid state interaction bandwidth for efficient operation. Similarly at reduced pressure but with several CO.sub.2 isotopologues pumped on selected rotational vibrational transitions of their respective 00.sup.00.fwdarw.20.sup.01 transitions the solid state interaction bandwidth will be adequate for efficient operation.

[0039] Coupling, or combination, of 2 m with 10 m cavity axis and mode volume via either dispersion in prisms or dichroic optics (FIG. 1. D & FIG. 2. D). Prisms cut with apex angle such that surface interactions are on Brewster angle for CO.sub.2 wavelength range, and near Brewster for 2 m pump. Prism material ideally low index as such typically reduces losses attributable to slight angular offsets.

[0040] Single or multi CO.sub.2 isotopologue gas mix situations are equally desirable from a system standpoint. Selection of gas mix and pressure to be utilized a function of intended application; high pressure and continuously tunable, near atmospheric or modest sub atmospheric and line tunable.

[0041] In pulsed high power optically pumped applications significantly sub atmospheric pressure not desirable as due to notably reduced relaxation rates alternate high gain transitions are not suppressed by excitation relaxation into the 00.sup.01 and 01.sup.11 levels, other than should those specific transitions be desired which amongst others include a band from 4.2 m to 4.3 m and a structure at 15.26 m. In some of the latter cases a resonant cavity is not necessarily required as gain is sufficiently high to result in amplified spontaneous emission.

[0042] Utilization of atmospheric, or higher, pressure non pumped low gain CO.sub.2 gas cells intra cavity (FIG. 1. D & FIG. 2. D) if required to suppress 4.2 m to 4.3 m and 15.26 m transitions is permitted. Low gain denotes spectrally selective absorption.

[0043] In a multi isotopologue gas mix, pumping of several isotopologues is preferable to pumping only one. At significant pressure this is less relevant as rate of cross relaxation to neighboring isotopologues increases.

[0044] Gas flow for thermal management at power, in reduced power applications diffusion cooling to waveguide or containment structure acceptable.

[0045] CO.sub.2 cavity optics commensurate with intended application. Tunable if continuous or line tunability required, otherwise simple broadband (FIG. 1. D & FIG. 2. D).

[0046] Intra CO.sub.2 cavity preferred use of transmitting optics (windows) at Brewster angle as this is favorable from a surface fluence reduction standpoint, plus minimizes Fresnel losses at 2 m and 10 m without need for dual wavelength anti reflection coatings (FIG. 1. D & FIG. 2. D).

[0047] The CO.sub.2 component isotopologue(s) may be admixed with at least one, or more, buffer gases selected from the group consisting of Helium, Argon and Nitrogen.

[0048] This laser diode excited, solid state pumped CO.sub.2 presents with a number of capabilities deriving from its particular features. Specifically, it is well suited to remote sensing applications requiring line or continuous tunability from 9 m through and above 11.5 m. Similarly, at pressure, it is suited to utilization as a broadband amplifier for sub picosecond pulse amplification and for high energy high power pulsed, or other applications requiring high energy pulsed output, disruption of thermal imaging systems of various types. Finally, utilization as a simple non tuned pulsed laser for industrial applications benefits from the methodologies general non dependence on an internal catalyzer for any meaningful gas lifetime.

[0049] The forgoing 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 the light of the above teaching. 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.