Laser Material Processing Division

Laser Separation of C-13 Isotop

C-13 isotope was successfully separated in grams quantity using high average power TEA CO₂ laser. The process of C-13 isotope separation involved selective multi-photon dissociation of C-13 bearing molecules having IR active vibrational bands over CO₂ laser wavelength. We  used Freon-22 (CF₂HCl) as reactant gas.  Freon-22 molecules were irradiated with short laser pulses at a fluence of 5 J/cm². By proper tuning of laser wavelength, C-13 bearing Freon-22 molecules were selectively dissociated forming a new compound C₂F₄ different than parent molecules. Selective dissociation process is shown in figure given below.

At working pressure of 100 mbar of Freon-22 gas, the absorption of laser energy in single pass iwas very low leading to low throughput of C-13 isotope and inefficient use of energy in the pulse. For efficient utilization of laser energy and high throughput, a novel Linear Multi-Pass Cavity (LMPC) was designed. The beauty of this multi-pass cell was that, the fluence remains constant in each pass irrespective of gradual decrease of laser energy due to absorption in each pass. Constant fluence in each pass was achieved by reducing the area by an amount equal to reduction in laser energy per pass. The repeated focusing action of laser energy in LMPC was simulated by passing He-Ne laser through this cavity instead of CO₂ laser, which is invisible.

Simulated Laser Beam Path in LMPC using He-Ne laser	Schematic of large irradiation cell

Using large irradiation cell of 110 lit volume, C-13 isotope was separated at a rate of 15 mg/h. The TEA CO₂ laser was operated at 100 Hz during the irradiation of Freon-22 in large cell.