Shanghai Institute of Optics and Fine Mechanics,Chinese Academy of Sciences
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Picosecond pulse compression by modulation of intensity envelope in a gas-filled hollow-core fiber
No full textNational Natural Science Foundation of China [61521093]; Strategic Priority Research Program of the Chinese Academy of Sciences [XDB1603]; International S&T Cooperation Program of China [2016YFE0119300]A method of temporally compressing picosecond pulses is proposed. To increase the spectral broadening, two picosecond pulses at different central wavelengths are overlapped spatiotemporally to induce a modulation on the intensity envelope, thus leading to a high temporal intensity gradient. The combined pulse is then coupled into a gas-filled hollow-core fiber (HCF) to broaden the spectrum through nonlinear propagation. After that the pulse can be compressed by chirp compensation. This method is demonstrated numerically with two 1-ps/5-mJ pulses centered at 1053- and 1064-nm, respectively, which are coupled into a 250-mu m-inner-diameter, 1-m-long HCF filled with 5-bar neon. After nonlinear propagation, the spectrum of the combined pulse is broadened significantly compared with the sum of the broadened spectra of a single 1-ps/10-mJ pulse centered at 1053- and 1064-nm. Under proper initial conditions, the pulse can be compressed down to similar to 16-fs. The influences of the energy ratio, time delay and wavelength gap between two input pulses, as well as the energy scaling are also discussed. These results show an alternative way to obtain ultrashort laser pulses from the picosecond laser technology, which can deliver both high peak power and high average power, and thus will benefit relevant researches in high-field laser physics
Self-compression of 1.8-mu m pulses in gas-filled hollow-core fibers
No full textNational Natural Science Foundation of China [61475169, 61521093, 11127901]; Chinese Academy of Sciences [XDB16]; International Science and Technology Cooperation Program of China [2016YFE0119300]We numerically study the self-compression of the optical pulses centered at 1.8-mu m in a hollow-core fiber (HCF) filled with argon. It is found that the pulse can be self-compressed to 2 optical cycles when the input pulse energy is 0.2-mJ and the gas pressure is 500-mbar (1 bar = 10(5) Pa). Inducing a proper positive chirp into the input pulse can lead to a shorter temporal duration after self-compression. These results will benefit the generation of energetic few-cycle mid-infrared pulses
Spatial chirp in Ti:sapphire multipass amplifier
No full text100 Talents Program of Chinese Academy of Sciences; National Natural Science Foundation of China [61475169, 61521093, 11127901]; Youth Innovation Promotion Association of Chinese Academy of SciencesThe spatial chirp generated in the Ti:sapphire multipass amplifier is numerically investigated based on the one-dimensional (1D) and two-dimensional (2D) Frantz-Nodvik equations. The simulation indicates that the spatial chirp is induced by the spatially inhomogeneous gain, and it can be almost eliminated by utilization of proper beam profiles and spot sizes of the signal and pump pulses, for example, the pump pulse has a top-hatted beam profile and the signal pulse has a super-Gaussian beam profile with a relatively larger spot size. In this way, a clear understanding of spatial chirp mechanisms in the Ti: sapphire multipass amplifier is proposed, therefore we can effectively almost eliminate the spatial chirp and improve the beam quality of a high-power Ti: sapphire chirped pulse amplifier system
Suppression of thermal lens effect in high-pulse-energy Ti:sapphire amplifiers
No full textNational Natural Science Foundation of China (NSFC) [11127901, 10734080, 61521093, 60908008, 61078037]; Youth Innovation Promotion Association CASIn high-pulse-energy Ti:sapphire amplifiers with moderate repetition rate, the thermal lens effect can significantly decrease the energy extraction efficiency and increase the risk of optical damage. A new method, without introducing any additional components, is proposed to suppress the thermal lens effect in such amplifiers. By utilizing a particularly designed beam expander before the amplifier, specific expanding ratio and beam divergence can be introduced to the injected seed pulses, which can improve the spatial matching between the seed pulses and the pump pulses, and thus enhance the energy extraction efficiency. The enhancement of the energy extraction efficiency has reached approximately 10% in our experimental four-pass Ti:sapphire amplifier, and the good agreement between theoretical and experimental results also demonstrates the validity and feasibility of this method. (C) 2016 Elsevier Ltd. All rights reserved
Measurement of mass by optical forced oscillation of absorbing particles trapped in air
No full textNational Youth Foundation of China [11504393]; National Natural Science Foundation of China (NSFC) [91536220]We demonstrate the application of optical forced oscillation to measure the mass of an absorbing microparticle trapped in air. When the light intensity is modulated sinusoidally, the particle in the trap undergoes forced oscillation, and the amplitude of the oscillation depends directly on the modulation frequency. We obtain the stiffness of the optical trap and the mass of the trapped particle by fitting the experimental data of the amplitudes versus the modulation frequencies with a simple spring model. The fitting results show that, for a certain particle, the stiffness varies linearly with the trapping light intensity while the mass is constant. The density of the microparticle is also estimated, which has potential to classify different kinds of absorbing particles, such as C and CuO
Quantum temporal imaging by four-wave mixing
No full textEuropean Union's Horizon Research and Innovation Programme (QCUMbER) [665148]We investigate temporal imaging of broadband squeezed light by four-wave-mixing. We consider two possible imaging configurations: phase-conjugating (PC) and phase-preserving (PP). Both of these configurations have been successfully used for temporal imaging of classical temporal waveforms. We demonstrate that for quantum temporal imaging, precisely, temporal imaging of broadband squeezed light, these two schemes have very different behavior: the PC configuration deteriorates squeezing, while the PP configuration leaves it intact. These results are very important for the applications of temporal imaging for quantum communications and quantum information processing
Bond-Selective Imaging of Cells by Mid-Infrared Photothermal Microscopy in High Wavenumber Region
No full textKeck Foundation Science and Engineering grant; UCAS Joint Ph.D. Training Program [UCAS [2015]37]Using a visible beam to probe the thermal effect induced by infrared absorption, mid-infrared photothermal (MIP) microscopy allows bond-selective chemical imaging at submicron spatial resolution. Current MIP microscopes cannot reach the high wavenumber region due to the limited tunability of the existing quantum cascade laser source. We extend the spectral range of MIP microscopy by difference frequency generation (DFG) from two chirped femtosecond pulses. Flexible wavelength tuning in both C-D and C-H regions was achieved with mid-infrared power up to 22.1 mW and spectral width of 29.3 cm(-1). Distribution of fatty acid in live human lung cancer cells was revealed by MIP imaging of the C-D bond at 2192 cm(-1)
High-Stability High-Energy Picosecond Optical Parametric Chirped Pulse Amplifier as a Preamplifier in Nd:Glass Petawatt System for Contrast Enhancement
No full textNational Natural Science Foundation of China [11604350, 61405211]We demonstrate a novel picosecond optical parametric preamplification to generate high-stability, high-energy and high-contrast seed pulses. The 5 ps seed pulse is amplified from 60 pJ to 300 mu J with an 8.6 ps/ 3mJ pump laser in a signal stage of short pulse non-collinear optical parametric chirped pulse amplification. The total gain is more than 106 and the rms energy stability is under 1.35%. The contrast ratio is higher than 108 within a scale of 20 ps before the main pulse. Consequently, the improvement factor of the signal contrast is approximately equal to the gain 106 outside the pump window
Mitigation of beam sampling grating damage induced by upstream flaws in the final optics assembly
No full textCollaboration on Advance Key Techniques for Inertial Fusion Energy [2012DFG62040]; National Natural Science Foundation of China [11104296]The high fluence performance of high-power laser systems is set by optical damage, especially in the final optics assembly (FOA). The flaws on the frequency converter surface can cause optical intensity intensification and, therefore, damage the downstream optical elements, such as the beam sampling grating (BSG), which is an important component in the FOA. Mitigation of BSG damage caused by flaws is discussed. Physical models are established to simulate the optical field enhancement on BSG modulated by the upstream flaw, considering both the linear and nonlinear propagation effects. Numerical calculations suggest that it is important to place the BSG in a properly selected position to mitigate the laser-induced damage. Furthermore, strict controls of flaw size, modulation depth, distance between frequency converter and focusing lens, and the thickness of the focusing lens are also significant to mitigate the BSG damage. The results obtained could also give some suggestions for damage mitigation of optical components and the layout design of the final optics assembly. (C) 2016 Society of Photo-Optical Instrumentation Engineers (SPIE
Structural evolution of axial intensity distribution during hot image formation
No full textThe structural evolution of the axial intensity distribution during hot image formation perturbed by a small circular optical obscuration is investigated in detail under different conditions. An analytic expression is derived for the axial intensity distribution around the conjugate plane by assuming the thickness of the nonlinear medium to be infinitely small. In view of the analysis of the axial intensity oscillation, the expression can be extensively utilized to characterize the intensity maxima for a nonlinear medium with a finite thickness. The nonlinear medium thickness and obscuration size both have great influence on the magnitudes and distributed features of the intensity maxima, which initially vary from multiple ones with comparable intensities to ultimately a maximum of one obviously remaining. The reason for this phenomenon is that the nonlinear medium acts like a low-pass filter to the scattering field, and optical interference exists between the scattering and background field. Furthermore, a fixed expression of nonlinear medium thickness and obscuration size is obtained to determine the dividing point of the alterations of the hot image intensity distribution. (C) 2017 Optical Society of Americ