Author Affiliations
Abstract
1 State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an710119, China
2 Key Laboratory for Physical Electronics and Devices of the Ministry of Education & Shaanxi Key Laboratory of Information Photonic Technique, Xi’an Jiaotong University, Xi’an710049, China
3 University of Chinese Academy of Sciences, Beijing100049, China
4 Key Laboratory on Applied Physics and Chemistry, Shaanxi Applied Physics and Chemistry Research Institute, Xi’an710061, China
5 Collaborative Innovation Center of Extreme Optics, Shanxi University, Taiyuan030006, China
Mode distortion induced by stimulated Raman scattering (SRS) has become a new obstacle for the further development of high-power fiber lasers with high beam quality. Here, an approach for effective suppression of the SRS-induced mode distortion in high-power fiber amplifiers has been demonstrated experimentally by adjusting the seed power (output power of seed source) and forward feedback coefficient of the rear port in the seed source. It is shown that the threshold power of the SRS-induced mode distortion can be increased significantly by reducing the seed power or the forward feedback coefficient. Moreover, it has also been found that the threshold power is extremely sensitive to the forward feedback power value from the rear port. The influence of the seed power on the threshold power can be attributed to the fact that the seed power plays an important role in the effective length of the gain fiber in the amplifier. The influence of the forward feedback coefficient on the threshold power can be attributed to the enhanced SRS configuration because the end surface of the rear port together with the fiber in the amplifier constitutes a half-opening cavity. This suppression approach will be very helpful to further develop the high-power fiber amplifiers with high beam quality.
high-power fiber amplifiers mode distortion stimulated Raman scattering suppression High Power Laser Science and Engineering
2021, 9(2): 02000e20
中国科学院西安光学精密机械研究所瞬态光学与光子技术国家重点实验室，陕西 西安 710119
从实验上研究了光电导天线电极之间激光光斑大小对太赫兹波产生的影响。另外，理论模拟了激光功率密度与太赫兹波辐射强度之间的关系，与实验结果非常吻合。泵浦光激光功率密度的增加能够显著的提高太赫兹波辐射强度，但是当超过一定值后会趋于饱和，此时若继续减小光斑尺寸，激光功率密度的增加不会使太赫兹产生继续增强。但是，太赫兹波却会随着光斑尺寸的减小而变弱。
太赫兹产生 光电导天线 激光功率密度 光斑尺寸 饱和 terahertz generation photoconductive antenna laser power density spot size saturation
Author Affiliations
Abstract
To suppress the fluctuation effect due to laser power instability and terahertz radiation fluctuation, a homomorphic filtering method is proposed to process the terahertz images obtained from a pulsed terahertz raster scanning imaging system. The physical model of homomorphic filtering for terahertz imaging is established. The mathematical expressions are given with the specific physical meaning in accordance with the imaging principle. To demonstrate the effectiveness of the method, a homomorphic filtering experiment based on two raw terahertz images selected from the literature using a continuous-wave (CW) terahertz source is also performed. The effect of the method is compared with those described in the literature, and the advantages of homomorphic filtering are discussed. The pulsed- and CW-terahertz image processing results both show that in addition to suppressing the fluctuation effect, the method can also enhance target imaging.
120.6200 Spectrometers and spectroscopic instrumentation 300.6495 Spectroscopy, teraherz 100.2960 Image analysis 100.2980 Image enhancement Chinese Optics Letters
2013, 11(8): 081201
Author Affiliations
Abstract
We experimentally investigate an optimum scheme of coupling a collimated light from a Ti:sapphire laser source into a standard single-mode fiber (SMF). By adjusting the effective numerical aperture (NA) of coupling lens and eliminating the chromatic aberration, a coupling efficiency of around 70% is finally obtained. This result is close to the maximum value predicted by theoretical simulation. It is well demonstrated that high coupling efficiency between Ti:sapphire laser and SMF can also be obtained by optimizing certain parameters of a coupling lens, without employing any special optical components, or the specific fiber with complex structure.
060.2430 Fibers, single-mode 010.3310 Laser beam transmission 140.3325 Laser coupling Chinese Optics Letters
2013, 11(5): 050605
Author Affiliations
Abstract
An overview of the major techniques to generate and detect THz radiation so far, especially the major approaches to generate and detect coherent ultra-short THz pulses using ultra-short pulsed laser, has been presented. And also, this paper, in particularly, focuses on broadband THz spectroscopy and addresses on a number of issues relevant to generation and detection of broadband pulsed THz radiation as well as broadband time-domain THz spectroscopy (THz-TDS) with the help of ultra-short pulsed laser. The time-domain waveforms of coherent ultra-short THz pulses from photoconductive antenna excited by femtosecond laser with different pulse durations and their corresponding Fourier-transformed spectra have been obtained via the numerical simulation of ultrafast dynamics between femtosecond laser pulse and photoconductive material. The origins of fringes modulated on the top of broadband amplitude spectrum, which is measured by electric-optic detector based on thin nonlinear crystal and extracted by fast Fourier transformation, have been analyzed and the major solutions to get rid of these fringes are discussed.
300.6495 Spectroscopy, teraherz 300.6270 Spectroscopy, far infrared 040.2235 Far infrared or terahertz 320.7160 Ultrafast technology Chinese Optics Letters
2011, 9(11): 110008
Author Affiliations
Abstract
In this letter, we employ terahertz time-domain spectroscopy (THz-TDS) technology to measure the THz absorption spectrum and refractive index of benzoic acid at room temperature. Linearity combination of atomic orbital (LCAO) within the density functional theory (DFT) is also used to compute the vibrational absorption spectra of benzoic acid in monomer and dimer. In addition, based on the results obtained from density functional calculation, the origins of observed intra-molecular and inter-molecular vibrational modes under specific peaks are interpreted.
300.6495 Spectroscopy, teraherz 040.2235 Far infrared or terahertz Chinese Optics Letters
2011, 9(s1): s10506
Author Affiliations
Abstract
The field of terahertz (THz) science and technology has achieved significant progress over the last decades. Research interest focuses on THz spectroscopy and imaging. The signal-to-noise ratio (SNR) of the THz system is of great importance in the application of THz spectroscopy and imaging. In this letter, the wavelet de-noising technology is used to improve SNR and increase the speed of the THz time-domain spectroscopy system by reducing the repeating times.
040.2235 Far infrared or terahertz 300.6495 Spectroscopy, teraherz Chinese Optics Letters
2011, 9(s1): s10504
Author Affiliations
Abstract
A new data-acquisition method based on the less movement of the time-delay stage is designed. The method can clearly reduce the time used in the entire imaging process in terahertz pulse imaging. According to the experimental result, the quality of imaging remains the same as the normal method or even better. The applicability and limitation of the method are also discussed.
110.2970 Image detection systems 110.6795 Terahertz imaging Chinese Optics Letters
2011, 9(s1): s10501
