Gamma-ray laser

{{Distinguish|text=gravity laser, also sometimes called a gaser or graser}}

A gamma-ray laser, or graser, is a hypothetical device that would produce coherent gamma rays, just as an ordinary laser produces coherent rays of visible light.{{cite journal|last=Baldwin|first=G. C.|year=1979|title=Bibliography of GRASER research|url=https://digital.library.unt.edu/ark:/67531/metadc1110382/|journal=Los Alamos Scientific Laboratory Report LA-7783-MS|doi=10.2172/6165356|osti=6165356}} Potential applications for gamma-ray lasers include medical imaging, spacecraft propulsion, and cancer treatment.{{cite web | url=https://news.ucr.edu/articles/2019/12/05/gamma-ray-laser-moves-step-closer-reality | title=Gamma-ray laser moves a step closer to reality | last=Pittalwala | first=Iqbal | date=2019-12-05 | website=University of California, Riverside | access-date=2022-11-27}}

In his 2003 Nobel lecture, Vitaly Ginzburg cited the gamma-ray laser as one of the 30 most important problems in physics.{{cite journal | last= Ginzburg | first=V. L. | year=2003 | title =On superconductivity and superfluidity | journal=The Nobel Prize in Physics 2003 | pages=96–127 | url= https://www.nobelprize.org/nobel_prizes/physics/laureates/2003/ginzburg-lecture.html}}

The effort to construct a practical gamma-ray laser is interdisciplinary, encompassing quantum mechanics, nuclear and optical spectroscopy, chemistry, solid-state physics, and metallurgy—as well as the generation, moderation, and interaction of neutrons—and involves specialized knowledge and research in all these fields. The subject involves both basic science and engineering technology.{{cite journal | last1=Baldwin | first1=G. C. | last2=Solem | first2=J. C. | last3=Gol'danskii | first3=V. I. | year=1981 | title=Approaches to the development of gamma-ray lasers | journal=Reviews of Modern Physics | volume=53 | issue=4 | pages=687–744 | doi=10.1103/revmodphys.53.687 | bibcode=1981RvMP...53..687B}}

Research

The problem of obtaining a sufficient concentration of resonant excited (isomeric) nuclear states for collective stimulated emission to occur turns on the broadening of the gamma-ray spectral line.{{cite journal | last1=Baldwin | first1=G. C. | last2=Solem | first2=J. C. | year=1979 | title=On the direct pumping of gamma-ray lasers by neutron capture | journal=Nuclear Science and Engineering | volume=72 | issue=3 | pages=290–292 | url= http://www.ans.org/pubs/journals/nse/a_20385| doi=10.13182/NSE79-A20385 }} Of the two forms of broadening, homogeneous broadening is the result of the lifetime of the isomeric state: the shorter the lifetime, the more broadened the line.{{cite journal | last1=Vali | first1=V. | last2=Vali | first2=W. | year=1963 | title= Induced gamma y-ray emission | journal = Proceedings of the IEEE | volume=51 | issue=1 | pages=182–184 | doi=10.1109/proc.1963.1677}}{{cite journal | last=Letokhov | first=V. S. | year=1973 | title=On the problem of the nuclear-transition gamma-laser | journal=Journal of Experimental and Theoretical Physics | volume=37 | issue=5 | pages=787–793 | url=http://www.jetp.ac.ru/cgi-bin/e/index/e/37/5/p787?a=list | access-date=2016-02-24 | archive-date=2016-03-11 | archive-url=https://web.archive.org/web/20160311171213/http://www.jetp.ac.ru/cgi-bin/e/index/e/37/5/p787?a=list | url-status=dead }}{{cite journal | last1=Kamenov | first1=P. | last2=Bonchev | first2=T. | year=1975 | title= On the possibility of realizing a gamma laser with long-living isomer nuclei | journal= Bolgarskaia Akademiia Nauk, Doklady | volume=28 |issue=9 | pages=1175–1177 | bibcode=1975BlDok..28.1175K}}{{cite journal | last1=Il'inskii | first1=Yu. A. | last2=Khokhlov | first2=R. V. | year=1976 | title= Possibility of creating a gamma-laser | journal= Radiophysics and Quantum Electronics | volume=19 | issue=6 | pages=561–567 | doi=10.1007/bf01043541| bibcode=1976R&QE...19..561I | s2cid=120340405 }} Inhomogeneous broadening comprises all mechanisms by which the homogeneously broadened line is spread over the spectrum.{{cite book | last=Baldwin | first=G. C. | chapter=On the Feasibility of Grasers | title=Laser Interaction and Related Plasma Phenomena | year=1977 | volume=4A | pages=249–257 | doi=10.1007/978-1-4684-8103-7_13| isbn=978-1-4684-8105-1 }}

The most familiar inhomogeneous broadening is Doppler recoil broadening from thermal motion of molecules in the solid containing the excited isomer and recoil from gamma-ray emission, in which the emission spectrum is both shifted and broadened. Isomers in solids can emit a sharp component superimposed on the Doppler-broadened background; this is called the Mössbauer effect.{{cite journal | last1=Andreev | first1=A. V. | last2=Il'inskii | first2=Yu. A. | last3=Khokhlov | first3=R. V. | year=1977 | title=Role of collective and induced processes in the generation of Mössbauer gamma radiation | journal=Journal of Experimental and Theoretical Physics | volume=46 | issue=4 | pages=682–684 | bibcode=1977JETP...46..682A | url=http://jetp.ac.ru/cgi-bin/e/index/e/46/4/p682?a=list | access-date=2016-02-24 | archive-date=2016-03-11 | archive-url=https://web.archive.org/web/20160311172259/http://jetp.ac.ru/cgi-bin/e/index/e/46/4/p682?a=list | url-status=dead }} This recoilless radiation exhibits a sharp line on top of the Doppler-broadened background that is only slightly shifted from the center of the background.{{cite journal | last=Hien | first=P. Z. | year=1970 | title=Spontaneous emission of gamma quanta by a system containing identical nuclei | journal=Journal of Experimental and Theoretical Physics | volume=31 | issue=1 | pages=83–86 | url=http://www.jetp.ac.ru/cgi-bin/e/index/e/31/1/p83?a=list | bibcode=1970JETP...31...83Z | access-date=2016-02-24 | archive-date=2016-03-11 | archive-url=https://web.archive.org/web/20160311172746/http://www.jetp.ac.ru/cgi-bin/e/index/e/31/1/p83?a=list | url-status=dead }}{{cite journal | last1= Gol'danskii | first1=V. I. | last2=Kagan | first2=Yu. M. | year=1973 | title= Feasibility of the nuclear-transition gamma laser (Graser) | journal= Soviet Physics Uspekhi | volume=16 | issue=4 | pages=563–565 | doi=10.1070/pu1974v016n04abeh005305}}{{cite journal | last=Namiot | first=V. A. | year=1973 | title=Stimulated line narrowing and the Mössbauer effect for long-lived isomers | journal=JETP Letters | volume=18 | issue=6 | pages=369–373 | url=http://www.jetpletters.ac.ru/ps/1564/article_23950.shtml | access-date=2016-02-24 | archive-date=2019-02-07 | archive-url=https://web.archive.org/web/20190207015355/http://www.jetpletters.ac.ru/ps/1564/article_23950.shtml | url-status=dead }}{{cite journal | last1=Andreev | first1=A. V. | last2=Il'inskii | first2=Yu. A. | last3=Khokhlov | first3=R. V. | year=1974 | title=Narrowing of gamma resonance lines in crystals by continuous radio-frequency fields | journal=Journal of Experimental and Theoretical Physics | volume=40 | issue=5 | pages=819–820 | url=http://www.jetp.ac.ru/cgi-bin/e/index/e/40/5/p819?a=list | bibcode=1975JETP...40..819A | access-date=2016-02-24 | archive-date=2016-09-27 | archive-url=https://web.archive.org/web/20160927201242/http://www.jetp.ac.ru/cgi-bin/e/index/e/40/5/p819?a=list | url-status=dead }}{{cite journal | last=Baldwin | first=G. C. |year=1979 | title= Time-domain spectroscopy of recoilless gamma rays | journal= Nuclear Instruments and Methods | volume=159 | issue=2–3 | pages=309–330 | doi=10.1016/0029-554x(79)90656-6| bibcode=1979NucIM.159..309B }}

With the inhomogeneous background removed, and a sharp line, it would seem that we have the conditions for gain.{{cite journal | last1=Terhune | first1=I. H. | last2=Baldwin | first2=G. C. | year=1965 | title= Nuclear superradiance in solids | journal= Physical Review Letters | volume=14 | issue=15 |pages=589–591 | doi=10.1103/physrevlett.14.589 | bibcode=1965PhRvL..14..589T}}{{cite book | last=Baldwin | first=G. C. | chapter=Is There a High Frequency Limit to Laser Action? | date=1974 | title=Laser Interaction and Related Plasma Phenomena | volume=3B | pages=875–888 | doi=10.1007/978-1-4684-8416-8_23| isbn=978-1-4684-8418-2 }}{{cite journal | last1=Andreev | first1=A V. | last2=Il'inskii | first2=Yu. A. | year=1975 | title=Amplification in a gamma laser when the Bragg condition is satisfied | journal=Journal of Experimental and Theoretical Physics | volume=41 | issue=3 | pages=403–405 | url=http://www.jetp.ac.ru/cgi-bin/e/index/e/41/3/p403?a=list | bibcode=1975JETP...41..403A | access-date=2016-02-24 | archive-date=2016-03-11 | archive-url=https://web.archive.org/web/20160311172745/http://www.jetp.ac.ru/cgi-bin/e/index/e/41/3/p403?a=list | url-status=dead }} But other difficulties that would degrade gain are unexcited states that would resonantly absorb the radiation, opaque impurities, and loss in propagation through the crystal in which the active nuclei are embedded.{{cite journal | last1=Il'inskii | first1=Yu. A. | last2=Khokhlov | first2= R. V. | year=1974 | title= On the possibility of observation of stimulated gamma radiation | journal= Soviet Physics Uspekhi | volume=16 | issue=4 | pages=565–567 | doi=10.1070/pu1974v016n04abeh005306}} Much of the latter can be overcome by clever matrix crystal alignment{{cite journal | last1=Baldwin | first1=G. C. | last2=Solem | first2=J. C. | year=1997 | title=Recoilless gamma-ray lasers | journal=Reviews of Modern Physics | volume=69 | issue=4 | pages=1085–1117 | doi=10.1103/revmodphys.69.1085 | bibcode=1997RvMP...69.1085B| url=https://zenodo.org/record/1233965 }} to exploit the transparency provided by the Borrmann effect.{{cite journal | last=Borrmann | first=G. | year=1941 | title= Über Extinktionsdiagramme der Röntgenstrahlen von Quarz | journal= Physikalische Zeitschrift | volume=42 | pages=157–162}}{{cite journal | last=Kagan | first=Yu. M. | year=1974 | title=Use of the anomalous passage effect to obtain stimulated emission of gamma quanta in a crystal | journal=JETP Letters | volume=20 | issue=1 | pages=11–12 | url=http://www.jetpletters.ac.ru/ps/1783/article_27177.shtml | access-date=2016-02-24 | archive-date=2016-09-06 | archive-url=https://web.archive.org/web/20160906105549/http://www.jetpletters.ac.ru/ps/1783/article_27177.shtml | url-status=dead }}{{cite journal | last1=Andreev | first1=A. V. | last2=Il'inskii | first2=Yu. A. | year=1976 | title=Possible use of the Borrmann effect in the gamma laser | journal=Journal of Experimental and Theoretical Physics | volume=43 | issue=5 | pages=893–896 | url=http://www.jetp.ac.ru/cgi-bin/e/index/e/43/5/p893?a=list | bibcode=1976JETP...43..893A | access-date=2016-02-24 | archive-date=2016-03-11 | archive-url=https://web.archive.org/web/20160311172748/http://www.jetp.ac.ru/cgi-bin/e/index/e/43/5/p893?a=list | url-status=dead }}

Another difficulty, the graser dilemma, is that properties that should enable gain and those that would permit sufficient nuclear inversion density seem incompatible.{{cite journal | last1=Baldwin | first1=G. C. | last2=Solem | first2=J. C. | year=1979 | title=Maximum density and capture rates of neutrons moderated from a pulsed source | journal=Nuclear Science and Engineering | volume=72 | issue=3 | pages=281–289 | url= http://www.ans.org/pubs/journals/nse/a_20384| doi=10.13182/NSE79-A20384 | bibcode=1979NSE....72..281B }}{{cite journal | last1=Baldwin | first1=G. C. | last2=Solem | first2=J. C. | year=1995 | title=Kinetics of neutron-burst pumped gamma-ray lasers | journal=Laser Physics | volume=5 | issue=2 | pages=326–335 | url= http://serials.unibo.it/cgi-ser/start/en/spogli/df-s.tcl?prog_art=2648750&language=ENGLISH&view=articoli}} The time required to activate, separate, concentrate, and crystallize an appreciable number of excited nuclei by conventional radiochemistry is at least a few seconds. To ensure the inversion persists, the lifetime of the excited state must be considerably longer. Furthermore, the heating that would result from neutron-pumping the inversion in situ seems incompatible with maintaining the Mössbauer effect, although there are still avenues to explore.{{Citation needed|date=February 2019}}

Heating may be reduced by two-stage neutron-gamma pumping,{{cite journal | last1=Gol'danskii | first1=V. I. | last2=Kagan | first2=Yu. | last3=Namiot | first3=V. A. | year=1973 | title=Two-stage pumping of Mössbauer gamma-ray lasers | journal=JETP Letters | volume=18 | issue=1 | pages=34–35 | url=http://www.jetpletters.ac.ru/ps/1539/article_23543.shtml | access-date=2016-02-24 | archive-date=2016-03-06 | archive-url=https://web.archive.org/web/20160306033600/http://www.jetpletters.ac.ru/ps/1539/article_23543.shtml | url-status=dead }} in which neutron capture occurs in a parent-doped converter, where it generates Mössbauer radiation that is then absorbed by ground-state nuclei in the graser.{{cite journal | last1=Gol'danskii | first1=V. I. | last2=Kagan | first2=Yu. | year=1973 | title=The possibility of creating a nuclear gamma laser | journal=Journal of Experimental and Theoretical Physics | volume=37 | issue=1 | pages=49 | url=http://www.jetp.ac.ru/cgi-bin/e/index/e/37/1/p49?a=list | bibcode=1973JETP...37...49G | access-date=2016-02-24 | archive-date=2016-03-11 | archive-url=https://web.archive.org/web/20160311172742/http://www.jetp.ac.ru/cgi-bin/e/index/e/37/1/p49?a=list | url-status=dead }}

Two-stage pumping of multiple levels offers multiple advantages.{{cite journal | last1=Baldwin | first1=G. C. | last2=Solem | first2=J. C. | year=1980 | title=Two-stage pumping of three-level Mössbauer gamma-ray lasers | journal=Journal of Applied Physics | volume=51 | issue=5 | pages=2372–2380 | doi=10.1063/1.328007| bibcode=1980JAP....51.2372B }}{{cite book | last=Baldwin | first=G. C. | chapter=Multistep Pumping Schemes for Short-Wave Lasers | title=Laser Interaction and Related Plasma Phenomena | year=1984 | volume=6 | pages=107–125 | doi=10.1007/978-1-4615-7332-6_8| isbn=978-1-4615-7334-0 }}{{clarify|date=February 2019}}

Another approach is to use nuclear transitions driven by collective electron oscillations.{{cite journal | last1=Solem | first1=J. C. | last2=Biedenharn | first2=L. C. | year=1987 | title=Primer on coupling collective electronic oscillations to nuclei | journal=Los Alamos National Laboratory Report LA-10878 | url= http://www.iaea.org/inis/collection/NCLCollectionStore/_Public/19/009/19009581.pdf| bibcode=1987pcce.rept.....S }}{{cite conference | last1=Biedeharn | first1=L. C. | last2=Baldwin | first2=G. C. | last3=Boer | first3=K. | year=1986 | title= Nuclear excitation by laser driven coherent outer shell electron oscillations | conference=Proceedings of the First International Laser Science Conference, Dallas, TX, November 18–22, 1985. Stwalley, W. C.; Lapp, M.; Eds. | volume=146 | pages=52–53 | doi=10.1063/1.35933 | bibcode=1986AIPC..146...52B }} The scheme would employ a triad of isomeric states: a long-lived storage state, in addition to an upper and lower lasing state.

The storage state would be energetically close to the short-lived upper lasing state but separated by a forbidden transition involving one quantum unit of spin angular momentum.

The graser would be enabled by a very intense optical laser to slosh the electron cloud back and forth and saturate the forbidden transition in the near field of the cloud.

The population of the storage state would then be quickly equalized with the upper lasing state whose transition to the lower lasing state would be both spontaneous and stimulated by resonant gamma radiation. A "complete" chart of nuclides likely contains a very large number of isomeric states, and the existence of such a triad seems likely, but it has yet to be found.{{cite journal | last1=Solem | first1=J. C. | last2=Biedenharn | first2=L. C. | last3=Rinker | first3=G. A. | year=1987 | title=Calculation of harmonic radiation from atoms subjected to strong laser fields and the possibility of nuclear excitation | journal=Journal of the Optical Society of America A | volume=4 | pages=53 | bibcode=1987JOSAA...4...53S}}

Nonlinearities can result in both spatial and temporal harmonics in the near field at the nucleus,{{cite journal | last1=Solem | first1=J. C. | last2=Biedenharn | first2=L. C. | year=1988 | title=Laser coupling to nuclei via collective electronic oscillations: A simple heuristic model study | journal=Journal of Quantitative Spectroscopy and Radiative Transfer | volume=40 | issue=6 | pages=707–712 | doi=10.1016/0022-4073(88)90066-0| bibcode=1988JQSRT..40..707S }}{{cite journal | last=Solem | first=J. C. | year=1988 | title=Theorem relating spatial and temporal harmonics for nuclear interlevel transfer driven by collective electronic oscillation | journal=Journal of Quantitative Spectroscopy and Radiative Transfer | volume=40 | issue=6 | pages=713–715 | doi=10.1016/0022-4073(88)90067-2| url=https://zenodo.org/record/1253954 | bibcode=1988JQSRT..40..713S }} opening the range of possibilities for rapid transfer from the storage state to the upper lasing state using other kinds of triads involving transition energies at multiples of the optical laser quantum energy and at higher multipolarities.

Gamma-ray laser

Research

See also

References

Further reading