Abstract
We employ the modified 6×6 matrix formalism to describe a pulsed Gaussian beam diffracted by a grating with arbitrary orientation. The matrix treatment is used to analyze the evolution of a pulsed beam propagating in a duplex grating compressor (DGC). For chirped pulse incidence, the inclination angle required in DGC setups will introduce several kinds of first-order spatio-temporal couplings (STCs). We found that temporal stretching due to spatial chirp is suppressed with enlarged beam diameter. Pulse-front tilt and residual frequency chirp in the compressed pulse will be eliminated simultaneously. Pulse with the transform-limited duration can be expected in ultra-intense and ultra-short pulse laser systems employing DGC.
© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
The invention of chirped pulse amplification (CPA) technique [1] and optical parametric chirped-pulse amplification (OPCPA) [2] enable laser pulses to be amplified safely by stretching pulses before the main amplifier. In the past decade, the final compressed peak power has been increased from hundreds of terawatt to multi-petawatt in ultra-high intensity laser facilities utilizing CPA and OPCPA [3–6]. More lasers are in the design phase or under construction for 10 PW worldwide, such as ELI [7], SULF [8], Vulcan-10PW [9], and Apollon-10PW [10]. The grating compressor is one of the key components in a CPA system which is inevitably exposed to the highest optical load for final high peak power pulsed laser output [11]. Gratings with larger aperture are commonly required in a CPA system in order to reduce the power density on the grating surface. Since the manufacture of large diffraction gratings is difficult and costly, alternative solutions have been proposed to improve the capacity of a compressor by relatively small-scale gratings. Tiled grating technique [12] allows sub-gratings to be tiled to form a large aperture grating; Bidirectional grating compressor (BGC) [13] presented a duplexing of the whole compressor in different directions; Object-image-grating self-tiling (OIGST) [14] uses a virtual image in the mirror to enlarge the effective grating aperture. Both OIGST and BGC can be regarded as duplex grating compressor (DGC).
In practice, spatio-temporal couplings (STCs) play a vital role in the transport and compression of an ultrashort pulsed beam. Recently, STCs act as a new degree of freedom for the control over the size, position, and movement of beam focus [15–18]. Although STCs can be useful in the optimization of nonlinear processes [19] and the generation of an attosecond pulse [20, 21], those couplings can lead to a strong reduction of intensity on the target in high power laser system [22]. Researchers are quite familiar with the pulse front tilt and angular dispersion caused by misaligned stretchers or compressors. Efforts have been made to analyze their influence on temporal change of pulses both theoretically and experimentally [23–27].
However, the spatio-temporal evolution of a pulse in DGC is more complicated than the pulse in a classical grating compressor because DGC commonly requires an inclination angle of incidence (also called out-of-plane tilt angle [28] upward/downward angle [29] or off-horizontal angle [30]) to avoid the back-reflection and to output the compressed pulse. In such condition, the evolution of an input pulse cannot be simplified as dispersing within the diffraction plane. Thus, application of DGC deserves careful investigation toward STCs, especially those stretching the compressed pulse duration.
The general theory of first-order STCs of Gaussian pulses and beams [31] provides complete definitions for first-order STCs, as well as a simple method to quantify them. The mathematical approach has a close relationship with ray-pulse matrices [32] because matrix formalism is convenient in dealing with the propagation of electromagnetic radiation in linear optical elements. In the past decades, several kinds of matrix approaches have been introduced to describe the beam propagation in pulse compressors and dispersive systems [33–36]. Kostenbauder introduced 4×4 ray-pulse matrices to model dispersive elements [32], which were further extended to 6×6 transfer matrix by Lin to analyze STCs in a grating-pair compressor [37]. Matrix treatments were not limited in describing Gaussian pulse. Yao generalized the formalism to describe random electromagnetic pulsed beam-like radiation interacting with linear optical elements [38]. Although 6×6 transfer matrix is capable in dealing with the evolution in both transverse coordinates, such transfer matrix has never been applied to model the 3D spatio-temporal evolution of a pulse in the grating-based system.
In this work, we modified the 6×6 matrix formalism to describe diffraction of a reflecting grating with arbitrary orientation and deal with general incident conditions. Matrix approach is applied to quantify STCs of compressed pulses in DGC. We find that the inclination angle in DGC leads to pulse front tilt and spatial chirp, which can stretch the output pulse. These calculations reveal the relationship of STCs with the attitude and position of gratings in DGC. Our approach can be used to guide the application and optimization of DGC in a high power laser system.
2. Matrix formalism
2.1. Definition of transfer matrix and generalized ABCD law
Before deriving the transfer matrix of grating with general incident conditions, we may review the definition of 6×6 transfer matrix and generalized ABCD law [37]. We define the beam path of the central frequency as the optical axis and construct the transverse coordinate at the input and output of a dispersive element. The output pulse parameters (subscript 2) of the dispersive element have the following relationship with the input pulse parameters (subscript 1):
2.2. Transfer matrix of arbitrarily oriented grating
To determine the transfer matrix of a grating, we construct a reference optical axis corresponding to the path of the central frequency. Then we define a grating coordinate system ${\hat{x}_g},{\hat{y}_g},{\hat{z}_g}$ and place the origin at the intersection of the optical axis and grating plane. Diffraction plane is defined as ${\hat{x}_g} - {\hat{z}_g}$ plane. We define local beam coordinate (${\hat{x}_1},{\hat{y}_1},{\hat{z}_1}$ for incident beam and ${\hat{x}_2},{\hat{y}_2},{\hat{z}_2}$ for diffracted beam) by constructing the transverse coordinate perpendicular to the reference axis and keeping ${\hat{x}_1},{\hat{x}_2}$ parallel to the diffraction plane. As is shown in Fig. 1, the orientation of a grating with respect to the incident optical axis is determined by $\alpha $ and $\theta $ [26], where $\alpha $ is the inclination angle, $\theta $ is the in-plane incident angle.
The in-plane diffraction angle $\phi $ for the central frequency ${\nu _0}$ satisfies the grating equation:
where m is the diffraction order, d is the groove spacing, ${\lambda _0}\textrm{ = }{c \mathord{\left/ {\vphantom {c {{\nu_0}}}} \right.} {{\nu _0}}}$ is the wavelength of the central frequency. The transfer matrix of the arbitrarily orientated grating is then determined by three variables:2.3. Transfer matrix of a duplex grating compressor
Let us consider a simple DGC setup in which the pulsed beam with an inclination angle $\alpha $ is sent into a parallel grating compressor. Grating grooves are set along the vertical direction. The transfer matrix of such compressor shown in Fig. 2 can be obtained by the ordered product of free propagation matrices and gratings’ transfer matrices:
In order to simplify our further analysis, consider the compressor with mirror symmetry where ${\theta _\textrm{1}}\textrm{ = }{\theta _\textrm{2}}\textrm{ = }\theta {\phi _\textrm{1}}\textrm{ = }{\phi _\textrm{2}}\textrm{ = }\phi$ and ${b_1} = {b_2} = b$. Each submatrix in ${\textbf M}$ is found by substituting Eq. (2) and Eq. (6) into Eq. (8)
3. Result and discussion
In this section, we calculated a chirped Gaussian pulse propagating in an ideal DGC as an example to help reveal STCs and their contribution to the compressed pulse duration. A simple method is also provided to compress the pulse to its transform-limited pulse duration. Our simulation based on a 15-mm radius, 25-fs transform-limited pulsed Gaussian beam centered at 800 nm which is stretched in an all-reflective Öffner type stretcher. The incident angle, the equivalent perpendicular distance of grating pair and the grating density are 52°, 985 mm and 1480 lines mm-1 respectively. The electric field of the stretched pulse is given by:
- (i) Global spectral phase: Group Delay Dispersion (GDD) and Third Order Dispersion (TOD). The global spectral phase is the global synchronization of the spectral components over the whole beam section. It is not a kind of STCs, but its compensation is quite crucial in designing a pulse compressor. For the standard grating pair compressor, the angle of incidence and the distance between gratings act as two degrees of freedoms and enables control over GDD and TOD [11]. In DGC setups, the same procedure can be applied [28]. Figure 3(a) shows the residual GDD when continuously adjusting the position and incident angle of the gratings in DGC. Dash line in Fig. 3(a) gives the incident angle and corresponding distance which compensate the TOD. The intersection point provides compensation of GDD and TOD simultaneously. From now on, our analysis will be confined nearby this point. The third order and higher order dispersion will be neglected.
- (ii) Amplitude coupling in the space-spectral domain: Spatial Chirp (SPC). From a geometrical perspective, the inclination angle, as well as the wavelength-dependent path length in DGC, can be regarded as the source of SPC. Since the wave vector has a vertical component, it is obvious that wavelength-dependent path length will cause vertical displacement [30]. Typically, the SPC should be normalized by the space and spectral width because the stretched duration depends on the spectral narrowing at the upper and lower edge of the beam’s cross section. Here in Fig. 3(b), SPC is normalized by the square root of both space and spectral width to provide a dimensionless coefficient. As shown in Fig. 3(b), the increased beam radius will minimize such spectral narrowing effect. The compressed pulse duration advances gradually to its transform-limited duration. For petawatt laser systems with meter-scale aperture, the stretching effect caused by SPC is negligible.
- (iii) Phase coupling in the space-spectral domain: Wave-front-tilt dispersion (WFD). In our calculation, the beam is well collimated and is free of angular dispersion. Therefore, we do not find significant WFD. Since the pulse width converges towards its transform-limited duration with enlarged beam size, the same conclusion can be directly derived by duration decomposing that the pulse is barely affected by phase coupling in the space-spectral domain.
- (iv) Another distinct coupling: Pulse-front tilt (PFT). Here in our calculation, when the grating distance slightly deviates from the optimum value (marked ‘A’ in Fig. 3 and Fig. 4), we found PFT to be raised. PFT is a well-known amplitude coupling in the spatial-temporal domain. It is usually observed in the system with angular dispersion [41] and is regarded as a fundamental coupling which stretches a pulse duration. However, PFT in DGC is generated by simultaneous temporal and spatial chirp [42]. Figure 4 shows the PFT normalized by the square root of space and temporal width and corresponding GDD when a 100 mm diameter pulse is sent in DGC. Following the decomposing procedure, we found that the stretching effect is already included in the global spectral phase mentioned above.
4. Conclusion
A generalized transfer matrix is derived for reflective grating. The matrix formalism is applied to investigate the first-order STCs implicated in DGC setups. We have demonstrated that SPC caused by inclination angle $\alpha $ will not seriously degrade the pulse duration in high power lasers which have huge beam apertures. Fine tuning of the grating distance is necessary to eliminate PFT and residual GDD in output pulse. When the gratings are set properly, DGC is expected to improve the output power by small gratings without inducing fatal STCs.
Funding
Strategic Priority Research Program of the Chinese Academy of Sciences (CAS) (XDB16030100); International S&T Cooperation Program of China (2016YFE0119300); Program of Shanghai Academic Research Leader (18XD1404200); Shanghai Municipal Science and Technology Major Project (2017SHZDZX02).
References
1. D. Strickland and G. Mourou, “Compression of amplified chirped optical pulses,” Opt. Commun. 56(3), 219–221 (1985). [CrossRef]
2. A. Dubietis, G. Jonušauskas, and A. Piskarskas, “Powerful femtosecond pulse generation by chirped and stretched pulse parametric amplification in BBO crystal,” Opt. Commun. 88(4-6), 437–440 (1992). [CrossRef]
3. C. Danson, D. Hillier, N. Hopps, and D. Neely, “Petawatt class lasers worldwide,” High Power Laser Sci. Eng. 3, e3 (2015). [CrossRef]
4. Y. Chu, X. Liang, L. Yu, Y. Xu, L. Xu, L. Ma, X. Lu, Y. Liu, Y. Leng, R. Li, and Z. Xu, “High-contrast 2.0 Petawatt Ti:sapphire laser system,” Opt. Express 21(24), 29231–29239 (2013). [CrossRef]
5. Z. Wang, C. Liu, Z. Shen, Q. Zhang, H. Teng, and Z. Wei, “High-contrast 1.16 PW Ti:sapphire laser system combined with a doubled chirped-pulse amplification scheme and a femtosecond optical-parametric amplifier,” Opt. Lett. 36(16), 3194–3196 (2011). [CrossRef]
6. L. Xu, L. Yu, X. Liang, Y. Chu, Z. Hu, L. Ma, Y. Xu, C. Wang, X. Lu, H. Lu, Y. Yue, Y. Zhao, F. Fan, H. Tu, Y. Leng, R. Li, and Z. Xu, “High-energy noncollinear optical parametric-chirped pulse amplification in LBO at 800 nm,” Opt. Lett. 38(22), 4837–4840 (2013). [CrossRef]
7. F. Batysta, R. Antipenkov, T. Borger, A. Kissinger, J. T. Green, R. Kananavičius, G. Chériaux, D. Hidinger, J. Kolenda, E. Gaul, B. Rus, and T. Ditmire, “Spectral pulse shaping of a 5 Hz, multi-joule, broadband optical parametric chirped pulse amplification frontend for a 10 PW laser system,” Opt. Lett. 43(16), 3866–3869 (2018). [CrossRef]
8. L. Yu, Y. Xu, Y. Liu, Y. Li, S. Li, Z. Liu, W. Li, F. Wu, X. Yang, Y. Yang, C. Wang, X. Lu, Y. Leng, R. Li, and Z. Xu, “High-contrast front end based on cascaded XPWG and femtosecond OPA for 10-PW-level Ti:sapphire laser,” Opt. Express 26(3), 2625–2633 (2018). [CrossRef]
9. C. Hernandez-Gomez, S. P. Blake, O. Chekhlov, R. J. Clarke, A. M. Dunne, M. Galimberti, S. Hancock, R. Heathcote, P. Holligan, A. Lyachev, P. Matousek, I. O. Musgrave, D. Neely, P. A. Norreys, I. Ross, Y. Tang, T. B. Winstone, B. E. Wyborn, and J. Collier, “The Vulcan 10 PW project,” J. Phys.: Conf. Ser. 244(3), 032006 (2010). [CrossRef]
10. D. N. Papadopoulos, P. Ramirez, K. Genevrier, L. Ranc, N. Lebas, A. Pellegrina, C. Le Blanc, P. Monot, L. Martin, J. P. Zou, F. Mathieu, P. Audebert, P. Georges, and F. Druon, “High-contrast 10 fs OPCPA-based front end for multi-PW laser chains,” Opt. Lett. 42(18), 3530–3533 (2017). [CrossRef]
11. I. V. Yakovlev, “Stretchers and compressors for ultra-high power laser systems,” Quantum Electron. 44(5), 393–414 (2014). [CrossRef]
12. J. Qiao, A. Kalb, T. Nguyen, J. Bunkenburg, D. Canning, and J. H. Kelly, “Demonstration of large-aperture tiled-grating compressors for high-energy, petawatt-class, chirped-pulse amplification systems,” Opt. Lett. 33(15), 1684–1686 (2008). [CrossRef]
13. C. Wang, Z. Li, S. Li, Y. Liu, Y. Leng, and R. Li, “Bidirectional grating compressors,” Opt. Commun. 371, 248–251 (2016). [CrossRef]
14. Z. Li, G. Xu, T. Wang, and Y. Dai, “Object-image-grating self-tiling to achieve and maintain stable, near-ideal tiled grating conditions,” Opt. Lett. 35(13), 2206–2208 (2010). [CrossRef]
15. C. G. Durfee and J. A. Squier, “Breakthroughs in Photonics 2014: Spatiotemporal Focusing: Advances and Applications,” IEEE Photonics J. 7(3), 1–6 (2015). [CrossRef]
16. G. Zhu, J. van Howe, M. Durst, W. Zipfel, and C. Xu, “Simultaneous spatial and temporal focusing of femtosecond pulses,” Opt. Express 13(6), 2153–2159 (2005). [CrossRef]
17. D. H. Froula, D. Turnbull, A. S. Davies, T. J. Kessler, D. Haberberger, J. P. Palastro, S.-W. Bahk, I. A. Begishev, R. Boni, S. Bucht, J. Katz, and J. L. Shaw, “Spatiotemporal control of laser intensity,” Nat. Photonics 12(5), 262–265 (2018). [CrossRef]
18. A. Sainte-Marie, O. Gobert, and F. Quéré, “Controlling the velocity of ultrashort light pulses in vacuum through spatio-temporal couplings,” Optica 4(10), 1298 (2017). [CrossRef]
19. O. Gobert, G. Mennerat, R. Maksimenka, N. Fedorov, M. Perdrix, D. Guillaumet, C. Ramond, J. Habib, C. Prigent, D. Vernhet, T. Oksenhendler, and M. Comte, “Efficient broadband 400 nm noncollinear second-harmonic generation of chirped femtosecond laser pulses in BBO and LBO,” Appl. Opt. 53(12), 2646–2655 (2014). [CrossRef]
20. H. Vincenti and F. Quere, “Attosecond lighthouses: how to use spatiotemporally coupled light fields to generate isolated attosecond pulses,” Phys. Rev. Lett. 108(11), 113904 (2012). [CrossRef]
21. J. A. Wheeler, A. Borot, S. Monchocé, H. Vincenti, A. Ricci, A. Malvache, R. Lopez-Martens, and F. Quéré, “Attosecond lighthouses from plasma mirrors,” Nat. Photonics 6(12), 829–833 (2012). [CrossRef]
22. G. Pretzler, A. Kasper, and K. J. Witte, “Angular chirp and tilted light pulses in CPA lasers,” Appl. Phys. B 70(1), 1–9 (2000). [CrossRef]
23. C. Fiorini, C. Sauteret, C. Rouyer, N. Blanchot, S. Seznec, and A. Migus, “Temporal Aberrations Due to Misalignments of a Stretcher Compressor System and Compensation,” IEEE J. Quantum Electron. 30(7), 1662–1670 (1994). [CrossRef]
24. S. W. Bahk, C. Dorrer, and J. Bromage, “Chromatic diversity: a new approach for characterizing spatiotemporal coupling of ultrashort pulses,” Opt. Express 26(7), 8767–8777 (2018). [CrossRef]
25. K. Osvay, A. P. Kovacs, Z. Heiner, G. Kurdi, J. Klebniczki, and M. Csatari, “Angular Dispersion and Temporal Change of Femtosecond Pulses From Misaligned Pulse Compressors,” IEEE J. Sel. Top. Quantum Electron. 10(1), 213–220 (2004). [CrossRef]
26. K. Osvay and I. N. Ross, “On a pulse compressor with gratings having arbitrary orientation,” Opt. Commun. 105(3-4), 271–278 (1994). [CrossRef]
27. S. Akturk, X. Gu, P. Bowlan, and R. Trebino, “Spatio-temporal couplings in ultrashort laser pulses,” J. Opt. 12(9), 093001 (2010). [CrossRef]
28. L. Zhaoyang, R. Daxing, L. Yuxin, C. Lei, and D. Yaping, “Third-order dispersion compensation for petawatt-level lasers employing object-image-grating self-tiling,” Quantum Electron. 45(10), 891–896 (2015). [CrossRef]
29. D. Daiya, R. K. Patidar, J. Sharma, A. S. Joshi, P. A. Naik, and P. D. Gupta, “Optical design and studies of a tiled single grating pulse compressor for enhanced parametric space and compensation of tiling errors,” Opt. Commun. 389, 165–169 (2017). [CrossRef]
30. Z. Zhang, S. Harayama, T. Yagi, and T. Arisawa, “Vertical chirp in grating pair stretcher and compressor,” Appl. Phys. Lett. 67(2), 176–178 (1995). [CrossRef]
31. S. Akturk, X. Gu, P. Gabolde, and R. Trebino, “The general theory of first-order spatio-temporal distortions of Gaussian pulses and beams,” Opt. Express 13(21), 8642–8661 (2005). [CrossRef]
32. A. G. Kostenbauder, “Ray-Pulse Matrices - a Rational Treatment for Dispersive Optical-Systems,” IEEE J. Quantum Electron. 26(6), 1148–1157 (1990). [CrossRef]
33. M. Nakazawa, H. Kubota, A. Sahara, and K. Tamura, “Time-domain ABCD matrix formalism for laser mode-locking and optical pulse transmission,” IEEE J. Quantum Electron. 34(7), 1075–1081 (1998). [CrossRef]
34. S. P. Dijaili, A. Dienes, and J. S. Smith, “Abcd Matrices for Dispersive Pulse-Propagation,” IEEE J. Quantum Electron. 26(6), 1158–1164 (1990). [CrossRef]
35. O. E. Martinez, “Matrix formalism for dispersive laser cavities,” IEEE J. Quantum Electron. 25(3), 296–300 (1989). [CrossRef]
36. O. E. Martinez, “Matrix Formalism for Pulse Compressors,” IEEE J. Quantum Electron. 24(12), 2530–2536 (1988). [CrossRef]
37. Q. Lin, S. Wang, J. Alda, and E. Bernabeu, “Spatial-temporal coupling in a grating-pair pulse compression system analysed by matrix optics,” Opt. Quantum Electron. 27(9), 785–798 (1995). [CrossRef]
38. M. Yao, Y. Cai, O. Korotkova, Q. Lin, and Z. Wang, “Spatio-temporal coupling of random electromagnetic pulses interacting with reflecting gratings,” Opt. Express 18(21), 22503–22514 (2010). [CrossRef]
39. https://github.com/YifeiArthur/Trasfer-matrix-of-the-compressor
40. C. Bourassin-Bouchet, M. Stephens, S. de Rossi, F. Delmotte, and P. Chavel, “Duration of ultrashort pulses in the presence of spatio-temporal coupling,” Opt. Express 19(18), 17357–17371 (2011). [CrossRef]
41. J. Hebling, “Derivation of the pulse front tilt caused by angular dispersion,” Opt. Quantum Electron. 28(12), 1759–1763 (1996). [CrossRef]
42. S. Akturk, X. Gu, E. Zeek, and R. Trebino, “Pulse-front tilt caused by spatial and temporal chirp,” Opt. Express 12(19), 4399–4410 (2004). [CrossRef]