LASER move to GASER

Laser has brought revolution in the technology. It is the symbol of precision and sharpness. A large amount of energy can be gathered in a very small area of micro-level in a very small time and that is why its intensity plays very important role to discuss different phenomena. It is widely used in the industry, engineering form wood-cutting to delicate medical operations.

It is based on the principle of stimulated atomic de-excitation from the metastable state (comparatively a long-lived state). From these atomic states we are able to get laser ranging from certain electronvolts (eV) to thousands of eVs. In this way, we can have laser of that much energy which is allowed by the atomic states. No doubt the intensity can control the operation of the processes but energy puts the limit on the scale via the wavelength which is in an inverse relation to energy that is why we cannot operate laser below the atomic scale i.e., at nuclear or particle level.

We have too big accelerators in the world as big as of CERN in Geneva of the dimensions of 27 km of diameter 100 meters below the Earth. These accelerators are used to accelerate the particles to very high energies which can be used to study the fundamental nature of the particles which is necessary to get knowledge about the beginning of the universe. It has too many applications like what is done in medical physics to cure cancer. It is like a dream of human kind to have such an accelerator which can be fixed on a table. Laser is considered one of the best candidates for the table-top accelerator.

To influence the nucleus we need energies of the order of MeVs (Million eVs) that is not achieved so far with laser. If it is achieved then photonuclear reactions would be realized by these multiphoton systems that can be controlled by laser intensities without the traditional accelerators rather with the help of these table-top accelerators. Now many questions can arise in the minds of readers that how will we create population inversion? How will we initiate the process? To answer these questions we can see that in nuclear physics we associate isomers with the nuclei. Isomers are long-lived nuclei. (We are familiar with the radioactive elements which emit radiations. They emit gamma rays since they are unstable. Half-life of different nuclei is different from fraction of seconds to millions of years which indicate that the nucleons stay in higher levels for different durations.) We can just make use of this fact and can have a population inversion to move to get laser out of nuclear states. This would essentially be gamma ray laser or can be abbreviated as GASER. You can envisage its strength as Gaser can be used to obliterate dinosaur as well as enormous Cities in seconds having gigantic energy.

Direct interaction of Laser and nucleus is not permissible so we can use some other phenomena such as NEEC (Nuclear Excitation by Electronic Capture) or NEET (Nuclear Excitation by Electronic Capture) to excite the nucleus by photon. When we interact laser with an atom the atom might excite by absorbing energy. Atomic transitions take place by the energy transferred to an atom in terms of laser. When the atom de-excites it emits some energy (photon) that might excite the nucleus of that atom for which resonance condition is required. For example in figure below the process is explained:

The left portion of each diagram contains the atomic states and the right portion expresses the nuclear states. There are certain states which are available where the resonance between the nuclear and atomic states is so available that when an excited atom de-excites then the emitted photon causes the nucleus to get excited. In initial state one can see that the electron is captured by an atom while the nucleus is in ground state. The electron moves to the ground state and the photon emits which has energy equal to the energy between the two states of the nucleus as expressed in resonant state in the figure and the nucleus gets excited. In the final state when the nucleus de-excites then a photon emits. Nuclear excitation is possible with or without laser. We concentrate here on the part played by laser. Laser is used as a connection or bridge between the atomic and nuclear states through which we are able to excite the nucleus which further helps us to populate the isomer state such that to have the condition to get laser i.e., gaser.

In 2011, Eugene Tkalya from the Institute of Nuclear Physics at Moscow State University has theoretically proven thorium isomer (^229mTh) feasible to produce Gaser. We need some energy or photon as a pumping source to initiate the process. Wherever we can use laser as a trigger to excite nucleons from ground state to some isomeric state which will work as a metastable state and in the case of Thorium it will be ^229mTh (where m denotes to isomeric state). Analogous with the case of laser the long life time of metastable or isomeric state will cause the augmentation of population in the metastable state. Tkalya mixed thorium with lithium-calcium-aluminium-fluoride (LiCaAlF₆) to obtain efficient results. He produced Gaser between states 3/2⁺ & 5/2⁺ with initial trigger energy 7.6 eV. Now, we will use some trigger to de-excite the metastable state having long half life that will cause production of Gamma rays from the nuclear states. Gaser has the energy beyond the limits which can be used as an immense source of energy to resolve the energy crises in the entire world. But there is need to use it positively instead of destruction as it takes years to build a city and seconds to destroy.

By Rana Umair Asif and Atif Shahbaz
*previously published in Scientific Ravi GC University Lahore