Input Signal Profile Influence on Output Spectra of Running Wave Amplifying Interferometer for Terahertz Spectroscopy

Abstract

The influence of the input signal temporal profile on output spectra of running wave amplifying interferometer (RWAI) is studied by mathematical modeling with the aim to make use of RWAI in terahertz spectroscopy. Two ways are considered : two frequency signal obtaining for further difference frequency signal extracting and reception of the required frequency as the spectrum component of sinusoidal signal modulated by terahertz frequency.The possibility of high-frequency modulation of laser radiation (GHz and THz orders of magnitude) without high-speed electronic control devices of corresponding frequencies was shown in [1]. The scheme under consideration (Fig. 1, a) consists of a beamsplitter with amplitude reflection factor, which can be conviniently designated as sin r (and, accordingly the amplitude transparency factor cos r , so the intensity reflection factor R and the intensity transparency factor T in sum give R+T= (sin r) 2 + (cos r ) 2 = 1) and a delay loop with delay time T1 to distinguish it from input wave period T. In the loop amplfier should be included with net unsaturated amplitude amplification factor Alfa>1 i.e. let the loop signal amplitude for each loop pass (between two consecutive splittings, hence without taking into account neither of them) be multiplied by Alfa. It was shown [1] that interference of two collinear running waves pairs on splitting surface along with amplification and delay of the resulting loop wave is capable to produce what we call balanced modulation -with constant amplitude of pulses formed and constant depth of modulation (both defined by Alfa or sin r because it occurs under balance condition Alfa = 1/sin r ).) b) Figure 1-a) general functional interference scheme under consideration, auxilliary mirrors or waveguides etc. missed out. b) modulation depth versus intensity reflection factor R=(sin r) 2