高強度的單次到次循環紅外光脈衝對於利用高階諧波產生來開發阿秒等級的極紫外光光源具有很強的潛力。為了獲取次循環脈衝，我們需要能準確量測脈衝相位資訊的工具，之後藉由量測結果來壓縮我們的脈衝使其成為單次到次循環脈衝。頻率解析光柵 (FROG) 是一種量測技術，由於其量測系統簡單且偵測敏銳，頻率解析光柵被廣泛地使用在實驗上。然而，其中相位的量測結果是藉由複雜的演算法所得到的。為了避免系統中非線性量測的過程和演算法所產生的錯誤，簡單直接的測量是比較適當的方法。頻譜干涉量測法（SI）是一種線性測量技術，可用於測量光譜相位。利用干涉頻譜和簡單的計算程式，我們可以還原我們的脈衝的光譜相位。
在這項工作中，我們可藉由白光干涉量測的方法來量測超短脈衝。白光干涉量測法不需要選擇特定的時間延遲來滿足信號處理的限制。經過量測第一級MPC所產生的30飛秒脈衝，並還原出其準確的光譜相位步驟之後。接下來我們根據我們的實驗結果設計客製化的啁啾反射鏡。並且成功利用啁啾反射鏡來補償我們的脈衝。同時轉換效率比我們以前使用的自製傅立葉壓縮系統提升許多（25.7% 提升至63％）。同時輸出能量能夠再進行一次MPC的實驗。最終，我們成功利用兩級的MPC系統產生單次循環脈衝，其脈衝寬為3.21飛秒。

Intense single -cycle infrared pulses have great potential to enable table-top isolated attosecond extreme ultraviolet (EUV) light source via high harmonic generation (HHG) process. In order to compress the pulse width down to single-carrier-cycle, some reliable metrology is required to accurately retrieve the spectral phase over the octave-spanning spectral range. Frequency resolved optical gating (FROG) is a widely used method. However, the nonlinear optical signal usually has a poor signal-to-noise ratio (SNR) and the iteratively reconstructed pulse information is subject to inherent uncertainty, which is particularly risky when octave-spanning bandwidth is involved. As a result, a linear and direct measurement technique is desired. White-light interferometry (WI) is a linear technique able to measure the spectral phase difference. In the presence of a transform-limited reference pulse, we can obtain the spectral phase of the signal pulse. Compared with another linear and direct method spectral interferometry, WI is immune to the trouble of choosing a proper delay to meet the criteria of data processing.
In this work, we utilize the WI scheme to analyze the phase information of single-cycle pulse. We first measure the pulse generated from the first Multi-plate Continuum (MPC) stage, and using the measured spectral phase for customizing chirped mirrors that can compress the MPC output pulse to 30 fs. The chirped mirrors substantially increase the conversion efficiency of nonlinear pulse compression (supercontinuum generation and spectral phase compensation) from 26% (using a homemade Fourier shaper) to 63%. The output pulse energy is therefore enough to initialize the second MPC stage, ending up with 3.21 fs pulse (below single-carrier-cycle) when a Fourier shaper is used for dechirping.

[1] R. R. Alfano and S. L. Shapiro, "Observation of self-phase modulation and small-scale filaments in crystals and glasses" Physical Review Letters 24, 592 (1970).
[2] Robert R. Alfano, The Supercontinuum Laser Source (Springer). 2006.
[3] A. Weiner, Ultrafast Optics (Wiley Series in Pure and Applied Optics). 2009.
[4] Jingsong Wei and Hui Yan, “Laser beam induced nanoscale spot through nonlinear “thick” samples: A multi-layer thin lens self-focusing model,” JOURNAL OF APPLIED PHYSICS, 116, 2014.
[5] Silva, F., et al. “Multi-octave supercontinuum generation from mid-infrared filamentation in a bulk crystal.” Nat. Commun. 3:807 doi: 10.1038/ncomms1816 (2012).
[6] Balciunas, T., et al. “A strong-field driver in the single-cycle regime based on self-compression in a Kagome fibre”. Nat. Commun. 6:6117 doi: 10.1038/ncomms7117 (2015).
[7] Steffen Hädrich, Marco Kienel, Michael Müller, Arno Klenke, Jan Rothhardt, Robert Klas, Thomas Gottschall, Tino Eidam, András Drozdy, Péter Jójárt, Zoltán Várallyay, Eric Cormier, Károly Osvay, Andreas Tünnermann, and Jens Limpert, “Energetic sub-2-cycle laser with 216 W average power,” Opt. Lett. 41, 4332–4335 2016.
[8] Chih-Hsuan Lu, et al “Generation of intense supercontinuum in condensed media.” Optica Vol. 1, No. 6(2014): 400-406.
[9] Yu-Chen Cheng, et al “ Supercontinuum generation in a multi-plate medium.” Optics Express 24.7 (2016):7224-7231.
[10] K. W. Delong, D. N. Fittinghoff, R. Trebino, B. Kohler, and K. Wilson, “Pulse retrieval in frequency‐resolved optical gating based on the method of generalized projections.,” Opt. Lett., vol. 19, no. 24, pp. 2152–2154, 1994.
[11] R. Trebino, K. W. Delong, D. N. Fittinghoff, J. N. Sweetser, M. A. Krumbügel, B. A. Richman, and D. J. Kane, “Measuring ultrashort laser pulses in the time‐frequency domain using frequency‐resolved optical gating,” Rev. Sci. Instrum., vol. 68, no. 9, pp. 3277–3295, 1997.
[12] R. Trebino and D. J. Kane, “Using phase retrieval to measure the intensity and phase of ultrashort pulses : frequency‐resolved optical gating,” vol. 10, no. 5, 1993.
[13] T. Wong and R. Trebino, “Recent Developments in Experimental Techniques for Measuring Two Pulses Simultaneously,” Appl. Sci., vol. 3, no. 1, pp. 299–313, 2013.
[14] T. C. Wong, M. Rhodes, and R. Trebino, “Single‐shot measurement of the complete temporal intensity and phase of supercontinuum,” Optica, vol. 1, no. 2, p. 119, 2014.
[15] A. S. Radunsky et al., “Simplified spectral phase interferometry for direct electric-field reconstruction by using a thick nonlinear crystal”, Opt. Lett. 31 (7), 1008, 2006.
[16] Ming-Chi Chen, Shang-Da Yang,“Measurement of Phase-Matching Spectral Phase by Nonlinear Spectral Interferometry”, 2011.
[17] I. a. Walmsley and C. Dorrer, “Characterization of ultrashort electromagnetic pulses,” Adv. Opt. Photonics, vol. 1, no. 2, p. 308, 2009.
[18] C. Dorrer and I. Kang, “Highly sensitive direct characterization of femtosecond pulses by electro-optic spectral shearing interferometry”, Opt. Lett. 28 (6), 477 , 2003.
[19] C. Dorrer et al., “Experimental implementation of Fourier-transform spectral interferometry and its application to the study of spectrometers”, Appl. Phys. B 70, S99, 2000.
[20] A. P. Kovacs et al., “Group-delay measurement on laser mirrors by spectrally resolved white-light interferometry”, Opt. Lett. 20 (7), 788, 1995.
[21] Q. Ye et al., “Dispersion measurement of tapered air–silica microstructure fiber by white-light interferometry”, Appl. Opt. 41 (22), 4467, 2002.
[22] P. Bowlan, P. Gabolde, and R. Trebino, “Directly measuring the spatio-temporal electric field of focusing ultrashort pulses,” Opt. Express 15, 10219-10230, 2007.