We present a review of the development of a compact and high-power broadband terahertz (THz) source optically excited by a femtosecond photonic crystal fiber (PCF) amplifier. The large mode area of the PCF and the stretcher-free configuration make the pump source compact and very efficient. Broadband THz pulses of 150 μW extending from 0.1 to 3.5 THz are generated from a 3-mm-thick GaP crystal through optical rectification of 12-W pump pulses with duration of 66 fs and a repetition rate of 52 MHz. A strong saturation effect is observed, which is attributed to pump pulse absorption; a Z-scan measurement shows that three-photon absorption dominates the nonlinear absorption when the crystal is pumped by femtosecond pulses at 1 040 nm. A further scale-up of the THz source power is expected to find important applications in THz nonlinear optics and nonlinear THz spectroscopy.

We present a thermal active control over terahertz (THz) extraordinary transmission induced by a plasmon in a periodic subwavelength holes array and a patch array. Both arrays consist of high transition temperature YBCO superconductors using THz time domain spectroscopy (THz-TDS). In the periodic subwavelength YBCO holes array, we observe a transition between a virtual excitation type surface plasmon polaritons (SPP) mode and a real SPP mode accompanied with transmission amplitude modulation. This can be attributed to the c-axis Josephson plasma frequency. On the other hand, since dipole localized surface plasmon can be excited by direct optical illuminations without phase-matching techniques, we observe a transmission amplitude modulation induced by combining the normal state carriers and the superconducting carriers in the periodic subwavelength YBCO patch array. These THz superconducting plasmonic crystals hold great potential in application for extreme low-loss, large dynamic amplitude modulation, surface plasmon-based function devices.

We investigate the optical response of silicon-based VxOy film for terahertz (THz) transmission. We find that absorption of the THz wave by the film can be controlled by laser excitation. Using THz time-domain spectroscopy (THz-TDS), we observe that the amplitude of the THz pulse is modulated by the external optical beam. The linearity of the optical modulation is also analyzed. Weak modulation nonlinearity is found to be within tolerable range.

We present a systematic study of freestanding terahertz (THz) metamaterials fabricated on Mylar film by self-aligned photolithography. THz time-domain spectroscopy (THz-TDS) transmission measurements and numerical simulations reveal the negative index of refraction in the frequency range of 0.66–0.90 THz under normal wave incidence. The observed resonance behaviors can be explained by a theoretical circuit model. The electromagnetic properties of such close-ring metamaterials are also explored in terms of geometrical parameters of the unit cell, thickness of the dielectric film, and conductivity of the close ring. This flexible metamaterial can pave the way for three-dimensional THz metamaterial fabrication and applications.

Nonlinear processes associated with terahertz radiation generated via optical rectification from undoped GaP crystal, including second harmonic generation (SHG) and multiphoton absorption processes, are examined. Experimental results of polarization-resolved SHG are obtained.

Conventional analytical methods in the wavelet domain are used to present an analysis of terahertz (THz) waveguide modes. To obtain THz radiation pulses passing through a waveguide, we build a simple experimental system with a 5-mm-long, 230-\mum-inner-diameter stainless steel waveguide. The single-mode guided signal from the experiments and the multi-mode signal of a similar THz waveguide reported in the literature are analyzed using the continuous wavelet transform (CWT). The results demonstrate that analyzing THz waveguide modes in the wavelet domain not only possesses all the functionality of the traditional THz time-domain spectroscopy (TDS) data processing but also has the ability to unscramble quantitatively and intuitively detailed information about the target samples, such as mode type, cut-off frequency, amplitude distinction, and group velocity.

光子晶体光纤(PCF)呈现出许多在传统光纤中难以实现的特性：可灵活设计的色散特性、增强的光学非线性特性、在极宽谱带内单模传输特性和增强的双折射特性等, 使其从一出现便受到了广泛关注并成为近年来光学与光电子学研究的一个热点, 在飞秒激光技术中得到了广泛的应用并极大地提高了锁模光纤激光器的输出水平。尤其以掺增益介质的双包层光子晶体光纤为代表的新型光纤激光技术的出现极大地推动了飞秒激光技术的普及化。阐述了近年来基于光子晶体光纤的飞秒激光振荡器、放大器方面的研究进展及其前沿应用。

In this letter, we describe a coherent subpicosecond terahertz (THz) spectroscopy system based on non-resonant optical rectification for the generation of THz radiation. We studied the two-photon absorption (TPA) of ZnTe induced by femtosecond laser pulses via THz generation, and its influence on the generation of THz radiation. Experimental results demonstrated that the intensity of pump beam against TPA must be traded off to get an optimum generation of THz radiation. As an example, we measured absorption spectrum of water vapor by time-domain spectroscopy (TDS) in the frequency range from 0.5 to 2.5 THz with a high overall accuracy.

本文对带有共焦光学延迟系统的8镜环形激光器的稳定域及腔内光束参数进行了系统的计算和分析,得到不同腔长时的最佳大曲率半径、腔长一定时的稳定域宽度以及腔内光束参数随大曲率半径的变化规律。

本文首次报道采用非谐振环实现Ar+激光器的脉冲碰撞锁模.分析了光腔的稳定性并给出初步研究结果.