We describe a novel electro-optic double-modulation ~DM! sampling technique for ultrafast transient spectroscopy, which is characterized by a superior signal-to-noise ratio compared to that of a regular single-modulation technique. DM is achieved by a combined effect of a radio-frequency modulation, which eliminates most of the low-frequency noise, and an audio-frequency modulation, which makes...

We report on a terahertz spectrometer for high-resolution molecular spectroscopy based on a quantum-cascade laser. High-frequency modulation (up to 50 MHz) of the laser driving current produces a simultaneous modulation of the frequency and amplitude of the laser output. The modulation generates sidebands, which are symmetrically positioned with respect to the laser carrier frequency. The molec...

nowadays, in the modern wars, radars have faced with many threats. therefore, low probability of interception (lpi) capability is considered as an important factor in military radars. on the other hand, research on the interception of their signals is started and so far several methods are presented for detection of these signals. by using of time-frequency techniques, we can estimate signal pa...

This article discusses the detection of mixed modulation, i.e., simultaneous amplitude and frequency modulation (MM). The investigations have incorporated both a sine wave modulating signal and an irregular modulating signal, a very narrow noise band, of a specified center frequency. The results revealed that for a sinusoidal low-frequency modulating signal, amplitude and frequency changes that...

Theory of Modulation Frequency Analysis and Modulation Filtering, with Applications to Hearing Devices Steven Marco Schimmel Chair of the Supervisory Committee: Professor Les E. Atlas Electrical Engineering Natural signals such as speech and music can be faithfully represented by low frequency modulators which modulate higher frequency carriers. In this work, a principled signal processing fram...