RESUMO
We report the operation of a 2 THz quantum cascade laser based on a GaAs/Al(0.1)Ga(0.9)As heterostructure. The laser transition is between an isolated subband and the upper state of a 14 meV wide miniband. Lasing action takes place on a high order vertical mode of a 200 microm thick double-metallic waveguide. In pulsed mode operation, with a 3.16mm long device, we report a threshold current density of 115 A/cm(2) at T = 4K, with a maximum measured peak power of 50 mW. The device shows lasing action in continuous wave up to 47K, with a maximum power in excess of 15 mW at T = 4K.
RESUMO
Results are presented for the first imaging system that combines the high power of terahertz quantum cascade lasers with three-dimensional image reconstruction based on filtered back-projection. Images of various phantoms have been successfully reconstructed revealing both their external and internal structures.
RESUMO
An imaging system in reflection geometry based on a multimode 2.9 THz quantum cascade laser as radiation source is reported. The beating between neighbouring longitudinal modes is detected using a room temperature point-contact Schottky diode as mixing element. We show that the technique can, in principle, give a dynamic range of 60 dB with a time constant of ~ 10 mus.
RESUMO
We compare terahertz-pulsed imaging (TPI) with transverse microradiography (TMR) and microindentation to measure remineralization of artificial caries lesions. Lesions are formed in bovine enamel using a solution of 0.1 M lactic acid/0.2% Carbopol C907 and 50% saturated with hydroxyapatite adjusted to pH 5.0. The 20-day experimental protocol consists of four 1 min treatment periods with dentifrices containing 10, 675, 1385, and 2700 ppm fluoride, a 4-h/day acid challenge, and, for the remaining time, specimens are stored in a 50:50 pooled human/artificial saliva mixture. Each specimen is imaged at the focal point of the terahertz beam (data-point spacing = 50 µm). The time-domain data are used to calculate the refractive index volume percent profile throughout the lesion, and the differences in the integrated areas between the baseline and post-treatment profiles are used to calculate ΔΔZ((THz)). In addition, the change from baseline in both the lesion depth and the intensity of the reflected pulse from the air/enamel interface is determined. Statistically significant Pearson correlation coefficients are observed between TPI and TMR/microindentation (P < 0.05). We demonstrate that TPI has potential as a research tool for hard tissue imaging.