At present, the mechanism and devices of terahertz radar detection and imaging has attracted a lot of interest. Based on 4-f terahertz time-domain spectroscopy (THz-TDS) technology, a broad-band time domain terahertz radar system (0.1- 1.3 THz) was built for scattering and imaging characteristics of objects. Far-field radar cross-section measurements of different metal scaled models at terahertz frequencies were performed. The novel broadband radar can provide RCS distributions at arbitrary frequency and frequency-averaged RCS. Moreover, based on improved filtered back projection algorithm, imaging of the scaled models has also been retrieved, which can be helpful for scattering points searching and military shape optimization.
We demonstrate a passively mode-locked all fiber ring laser based on all-solid Yb-doped Photonic Bandgap fiber (AS-Yb-
PBGF) which is designed to simultaneously provide laser gain and anomalous dispersion. The laser is comprised of
0.42m AS-Yb-PBGF and a segment of single mode fiber (SMF). By varying the length of the SMF from 0.8m to 3.2m,
three operation schemes, namely soliton operation, gain-guided soliton operation, and self-similarity operation, have
been obtained by means of numerical simulations in split-step Fourier method in the ring laser. In the case of net
anomalous cavity group-velocity dispersion (GVD) when the SMF is 0.8m, we obtain soliton pulse with the balance
between the nonlinear self-phase modulation (SPM) and the anomalous GVD. The soliton pulse has the pulse duration of
355fs and the bandwidth of 1.9nm, corresponding to the time-bandwidth product of 0.33, nearly a transform-limited
pulse. As the length of the SMF is changed to 2m, self-similar propagation is generated with the net cavity GVD of
+0.014ps<sup>2</sup>. The pulse has strong frequency chirp and high pulse energy up to 4nJ. The pulse duration is 2.5ps with the
bandwidth of 2.1THz. To obtain gain-guided soliton, we change the SMF to 3.2m leading to a large net positive cavity
GVD of +0.04 ps<sup>2</sup> and enforce the spectral limit of the gain fiber. A chirped gain-guided soliton pulse is observed with
pulse energy of ~1nJ, the pulse duration of 2.5ps and the bandwidth of 2.5 THz.