Exploring new active materials for low-noise room-temperature microwave amplifiers and other devices

Newly discovered chemical systems, mainly the C-60 molecule (a molecule con taining 60 carbon atoms) and porphyrin molecules tone of the basic building blocks of the hemoglobin and chlorophyll molecules) dissolved in organic s olvents, have been considered as active microwave amplifying or absorbing m aterials. These effects are obtained under an external de magnetic field as well as optical excitation. These materials are potentially important in c ertain applications in microwaves, In this paper, an attempt is made at eva luating this potential. To this end, the complex permeability of the dissol ved C-60 molecules has been measured, under the aforementioned physical con ditions, in three different experiments with the aid of three types of elec tron paramagnetic resonance (EPR) spectrometers, respectively. The permeabi lity of the C-60 molecules, when dissolved in liquid toluene, has been foun d to have a negative imaginary part of about mu(r)" = -0.0055 (i.e., attenu ating for the e(jwt) harmonic time dependence) over a bandwidth of 0.4 MHz around the center frequency, which is known as the Larmor frequency, and is determined by the external de magnetic field. Alternatively, the same mole cules, when dissolved in a nematic liquid crystal (LC), have either positiv e (amplifying) or negative (absorbing) mu(r)", with absolute value of about 0.005 over a bandwidth of 27 MHz, All measurements have been taken around the temperature of T = 253 K, The lifetime of the phenomenon, during the ti me span that follows the laser optical excitation, is about 10 mu s. The ap plicability of those materials for solid state optically pumped maser ampli fiers, which operate at room temperature with a very low-noise temperature or for other novel devices, is demonstrated in this paper.