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 approximately 9 m to approximately 11.5 m, or sub picosecond amplification. This method 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, a laser diode excited Tm solid state laser tuned to the 00.sup.00.fwdarw.20.sup.01 combination band transition(s) of CO.sub.2 isotopologue(s) to be optically pumped for lasing purposes; a gas containment structure with selected CO.sub.2 gas mix and admixture gas components and at pressure for line tunability or continuous tunability, located internal to a resonant cavity; a pump beam and, a CO.sub.2 cavity axis combination method imposing pump beam CO.sub.2 gas interaction; the CO.sub.2 laser producing an output in an atmospheric optical transmission window within a spectral region from approximately 9 m to approximately 11.5 m.

2. An optically pumped CO.sub.2 laser, according to claim 1, wherein for the optically pumped CO.sub.2 at pressure, a laser diode pumped solid state system's efficiency is not limited by molecular line widths and 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 a single or multi isotopologue CO.sub.2 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 lasing in the defined approximately 9 m to approximately 11.5 m range include the 00.sup.01 and 01.sup.11 levels.

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

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

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

8. An optically pumped CO.sub.2 laser, according to claim 1, wherein the pumped CO.sub.2 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.

9. An optically pumped CO.sub.2 laser comprising, a sustained and preserved single or multi-CO.sub.2 isotopologue mix, the mix having symmetric and asymmetric components, the mix capability courtesy of absence of gas mix perturbation by molecular dissociation driven recombination.

10. An optically pumped CO.sub.2 laser according to claim 9, wherein a CO.sub.2 cavity, absent said molecular dissociation, allows utilization of an arbitrarily proportioned multi isotopologue CO.sub.2 gas mix, with an optimal line tunability from approximately 9 m through approximately 11.5 m at atmospheric or modest sub atmospheric pressure, and continuous tunability from approximately 9 m through approximately 11.5 m at high pressure.

11. An optically pumped CO.sub.2 laser, according to claim 9, wherein the optically pumped CO.sub.2 laser is used in, given spectral tunability, a system for remote sensing of agents of interest in the approximately 9 m to approximately 11.5 m spectral range.

12. An optically pumped CO.sub.2 laser, according to claim 9, wherein at a pressure a system is enabled which is suitable for use for short pulse amplification of approximately 10 m CO.sub.2 laser output into the sub_picosecond timescale.

13. An optically pumped CO.sub.2 laser, according to claim 9, wherein using the feasibility of utilization of asymmetric isotopologues and/or a 01.sup.11 excited level, a-system gas pressure required for continuous tunability is 50% or less than that required for the purely symmetric isotopologues.

14. An optically pumped CO.sub.2 laser, according to claim 9, wherein absent the molecular dissociation, a catalyzer is not a system requirement.

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 an illustration of the pulsed manifestation of the invention. The CO.sub.2 laser cavity is comprised of a resonant cavity for CO.sub.2 optical radiation plus a containment structure for the CO.sub.2 gas mix. The cavity axis conforms to the indicated 10 m beam output direction (E), and thus the one-dimensional resonant cavity characteristic of lasers requiring resonant cavities. 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, or by definition pump beam, via spectral beam combiner (or dichroic optics) to admit introduction to CO.sub.2 laser cavity (D) with 10 m output (E).

(3) FIG. 2: Is an illustration of the CW manifestation of the invention. The CO.sub.2 laser cavity is comprised of a resonant cavity for CO.sub.2 optical radiation plus a containment structure for the CO.sub.2 gas mix. The cavity axis conforms to the 10 m beam output direction (E), and thus the one-dimensional resonant cavity characteristic of lasers requiring resonant cavities. 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, or by definition pump beam, via suitable beam combiner or dichroic optics, into CO.sub.2 laser cavity (D) with 10 m output (E).

(4) 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

(5) 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, YAG being just one example) and thus energy and or 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.12O.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.

(6) The laser diode excited Tm doped solid state optical pump approach to CO.sub.2 is absent the high voltage switching, discharge electrode erosion, resulting in limited time between scheduled maintenance, 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.

(7) 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 symmetric isotopologue case and thus will be continuously tunable at a pressure below that required for the symmetric isotopologue zero angular momentum metastable level.

(8) 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 (symmetric and asymmetric) 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.

(9) 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.

(10) 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. 1A, B, C.

(11) 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.

(12) 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.

(13) 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.

(14) 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.

(15) 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.

(16) 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.

(17) 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.

(18) Gas flow for thermal management at power, in reduced power applications diffusion cooling to waveguide or containment structure acceptable.

(19) 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).

(20) 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).

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

(22) 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.

(23) 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.