Ultrafast Optical Technology Based On Spectrum Control

In recent decades, ultrafast optics have got a great development and become more and more mature. Many ultrafast optical devices, which can only work as laboratory tools in the past, now has developed into a popular or even commercial products. Simultaneously, the rapid development of ultrafast optics also results in some revolutions in scientific frontiers, opens up some unprecedented fields, e.g. ultra-strong physics, attosecond optics. As indispensable platforms, ultrafast optical systems are widely applied in many areas such as physics, chemistry, biology, medicine, and involves the military, aerospace, scientific research, medical treatment and industry and so on. All above show ultrafast optical technology is significant for modern social and economic developments.Ultrafast optics depends strongly on generation and detection of ultrashort laser pulses. One of the inherent properties of ultrashort laser pulses is broad spectrum, so, spectrum control plays an important role in the process of generation and detection of ultrashort laser pulses and ultrafast signals. This thesis focuses on ultrafast optical technology based on spectrum control, includingTo avoid spectrum narrowing effect, thus obtain higher ultrashort pulse peak power in chirped pulse amplification(CPA) system by controlling spectrum of gain crosssection.Due to the limited gain width, CPA systems usually have different amplification effect for different frequency component: component away from the central frequency get the less amplification than component close to the central. As a result, the spectral narrowing occurs during amplification, which leads to longer compressed pulse duration and lower output pulse power.A novel passive method is put forward to compensate the gain narrowing in polarization-dependent Ti:S amplifiers basing on optical rotatory dispersion. Here, the different spectral components of chirp pulses are with different polarization directions, so the gain cross-section of the laser amplifiers can be modulation flexibly to avoid the gain narrowing.(2) To improve the direct electric-field reconstruction of ultrashort laser pulses by introducing two-step phase-shift, which allows the traditional SPIDER to work more accurately, robustly to recover ultrashort pulse field both in time and spectral domains, includingTraditional SPIDER algorithm needs a Fourier transform of spectrum interference fringes to get temporal signal, and a window filtering to get the alternating component. When the spectrum of ultrashort pulse has complex temporal or spectral structures, the window filtering may fail to pick up the alternating component clearly and completely, which can lead to measurements results associated with the selection of window, thus reduce the robustness and accuracy of the measurements.By introducing two-step phase-shift in SPIDER, we can eliminate experimentally the DC components of the recorded interferences, thus filter the paragraphs AC from DC perfectly. Due to no longer need of the window function to intercept the AC, this method can reduce the reliance on algorithm, improve the reliability and accuracy of the measurement result, and widen measurable range.To develop novel spectral interference for terahertz pulse information decoding, which provide a way of parallel high linearity measurements, includingElectro-optic sampling is commonly used for measurements of terahertz pulse. Electro-optic sampling can be divided into time division electro-optic sampling and spectral encoding electro-optic sampling, the spectral encoding electro-optic sampling can realize parallel data sampling, sampling rate is higher than in time division electro-optic sampling. At the same time, electro-optic sampling at nearzero optical transmission point can obtain high modulation of terahertz pulse measurement. However, the traditional electro-optic sampling are based on electro-optical effect which change detection of polarization of probe light, after polarizer to detect the light intensity of the transformation of the terahertz signal to reflect the terahertz strength. This method is applicable which terahertz pulse intensity is weak, but for the strong terahertz pulse intensity, the modulation distortion will happen happened which cannot reflect the THz waveform.We present a terahertz time-domain spectroscopy technology based on spectral interference,spectral encoding and electro-optic sampling. Compared with the traditional time domain spectrometer, this technology possesses the advantages of real-time and high linearity, which is proven to be suitable for measuring strong intensity THz signal.