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[IEEE 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Munich, Germany (2019.6.23-2019.6.27)] 2019 Conference on Lasers and Electro-Optics Europe & European Quantum Electronics Conference (CLEO/Europe-EQEC) - Characterization of 8 fs Deep-UV Pulses using XPW Dispersion Scan
摘要： The measurement of few-fs-long deep-ultraviolet (DUV) pulses is one of the most demanding tasks for optical pulse characterization as these pulses are very much prone to material dispersion and space-time distortions. Therefore, the arrangements should be very carefully designed not to deteriorate the pulses in the course of the measurement. Furthermore, in this wavelength range the most popular nonlinearities used for the characterization such as second harmonic or sum frequency generation processes become unpractical or even unfeasible due to the very limited phase-matching or the even shorter wavelength of the resulted signal. Consequently, up to now most of short UV pulses were characterized by the FROG technique utilizing a degenerate four-wave mixing process, such as self diffraction [1] or transient grating formation [2]. Nevertheless, this technique suffers from rather bad signal to noise ratio and low sensitivity due to wave front splitting necessary for such method. Here we demonstrate for the first time the measurement of 8 fs DUV pulses using a dispersion scan (d-scan) apparatus. We use cross-polarized wave (XPW) generation, another degenerate four-wave mixing process without frequency conversion, as the nonlinear process [3], as we have already implemented for the characterization of few-cycle near infrared pulses [4,5]. Thanks to the single-beam geometry of d-scan no beam splitting is necessary, dramatically improving the sensitivity of the measurement and reducing the stray light. As a result we can measure DUV pulses with energy as low as 85 nJ with high fidelity. Figures 1(a) and 1(b) show the measured and retrieved d-scan traces of the UV pulses with RMS error of 2%, proving the robustness of the measurement. The retrieved pulse shape as well as the spectral intensity and the phase are displayed in Figs. 1(d) and 1(c), respectively. The generation of slightly negatively chirped 8 fs UV pulses is based on indirect pulse shaping approach [6]. Negatively chirped broadband pulses at 800 nm from a 3-m-long stretched flexible hollow fiber and a subsequent chirped mirror compressor are mixed in a 5 μm BBO crystal with narrowband pulses at 400 nm (second harmonic of the fundamental pulse). In the course of sum frequency generation the negative chirp of the broadband pulse is transferred into the UV. For the pulse characterization, the XPW signal is generated in a 50 μm thick barium fluoride crystal and the signal is filtered by a Glan-Laser polarizer. With these results we demonstrate that XPW d-scan has a great potential for the characterization of very short pulses throughout the wide transparency range of barium fluoride from the deep-UV up to the mid-IR making this technique very versatile.
关键词： pulse characterization,dispersion scan,deep-ultraviolet pulses,XPW generation
更新于2025-09-16 10:30:52
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Ultrashort pulse reconstruction using a deterministic phase retrieval method with Gaussian-envelope gates
摘要： A novel scheme of ultrashort pulse characterization is proposed that is capable of reconstructing the complex-valued envelope of a pulse in the time domain by use of a second harmonic generation system with two Gaussian gate pulses. In this scheme, we apply an analytic (noniterative) phase-retrieval method for coherent diffractive imaging in the space domain to the pulse characterization, and so the spectral phase of an unknown pulse can be retrieved from only two spectra of the unknown pulse modulated with a Gaussian gate and its time-shifted Gaussian one. Computer-simulated examples demonstrate that the pulse retrieval is robust. In particular, it is shown that the reconstruction of an unknown pulse using approximate Gaussian gates derived from replicas of the pulse itself is also effective, provided the spectrum of the unknown pulse has a gentle slope within the spectral bandwidth of the gate pulse.
关键词： Ultrafast measurements,Pulse characterization,Phase retrieval,Ultrafast optics
更新于2025-09-09 09:28:46