Coherent anti-Stokes Raman spectroscopy utilizing phase mismatched cascaded quadratic optical interactions in nonlinear crystals Georgi I. Petrov,1 Miaochan Zhi,2 and Vladislav V. Yakovlev1,* 1

Department of Biomedical Engineering, Texas A&M University, College Station, Texas 77843-3120, USA 2 Currently at NIST, 100 Bureau Drive, Gaithersburg, Maryland 20899-8543, USA * [email protected]

Abstract: We experimentally investigated the nonlinear optical interaction between the instantaneous four-wave mixing and the cascaded quadratic frequency conversion in commonly used nonlinear optical KTP and LiNbO3 with the aim of a possible background suppression of the non-resonant background in coherent anti-Stokes Raman scattering. The possibility of background-free heterodyne coherent anti-Stokes Raman scattering microspectroscopy is investigated at the interface formed by a liquid (isopropyl alcohol) and a nonlinear crystal (LiNbO3). ©2013 Optical Society of America OCIS codes: (190.7110) Ultrafast nonlinear optics; (190.4720) Optical nonlinearities of condensed matter; (290.5860) Scattering, Raman; (180.5655) Raman microscopy.

References and links 1. 2. 3. 4. 5. 6. 7. 8. 9. 10. 11. 12. 13. 14. 15. 16.

J. Cheng and X. S. Xie, Coherent Raman Scattering Microscopy (CRC Press, 2012). R. Arora, G. I. Petrov, and V. V. Yakovlev, “Analytical capabilities of coherent anti-Stokes Raman scattering microspectroscopy,” J. Mod. Opt. 55(19-20), 3237–3254 (2008). R. Arora, G. I. Petrov, V. V. Yakovlev, and M. O. Scully, “Detecting anthrax in the mail by coherent Raman microspectroscopy,” Proc. Natl. Acad. Sci. U. S. A. 109(4), 1151–1153 (2012). L. A. Golovan, K. A. Gonchar, L. A. Osminkina, V. Y. Timoshenko, G. I. Petrov, and V. V. Yakovlev, “Coherent anti-Stokes Raman scattering in silicon nanowire ensembles,” Laser Phys. Lett. 9(2), 145–150 (2012). R. Arora, G. I. Petrov, and V. V. Yakovlev, “Hyperspectral coherent anti-Stokes Raman scattering microscopy imaging through turbid medium,” J. Biomed. Opt. 16(2), 021116 (2011). D. Oron, N. Dudovich, and Y. Silberberg, “Femtosecond phase-and-polarization control for background-free coherent anti-Stokes Raman spectroscopy,” Phys. Rev. Lett. 90(21), 213902 (2003). D. Pestov, R. K. Murawski, G. O. Ariunbold, X. Wang, M. C. Zhi, A. V. Sokolov, V. A. Sautenkov, Y. V. Rostovtsev, A. Dogariu, Y. Huang, and M. O. Scully, “Optimizing the laser-pulse configuration for coherent Raman spectroscopy,” Science 316(5822), 265–268 (2007). X. Wang, A. Zhang, M. Zhi, A. V. Sokolov, G. R. Welch, and M. O. Scully, “Heterodyne coherent anti-Stokes Raman scattering for spectral phase retrieval and signal amplification,” Opt. Lett. 35(5), 721–723 (2010). G. I. Petrov, R. Arora, V. V. Yakovlev, X. Wang, A. V. Sokolov, and M. O. Scully, “Comparison of coherent and spontaneous Raman microspectroscopies for noninvasive detection of single bacterial endospores,” Proc. Natl. Acad. Sci. U. S. A. 104(19), 7776–7779 (2007). M. T. Cicerone, K. A. Aamer, Y. J. Lee, and E. Vartiainen, “Maximum entropy and time-domain Kramers– Kronig phase retrieval approaches are functionally equivalent for CARS microspectroscopy,” J. Raman Spectrosc. 43(5), 637–643 (2012). B. B. Zhou, A. Chong, F. W. Wise, and M. Bache, “Ultrafast and octave-spanning optical nonlinearities from strongly phase-mismatched quadratic interactions,” Phys. Rev. Lett. 109(4), 043902 (2012). R. Boyd, Nonlinear Optics, 3rd ed. (Academic, 2008). M. Bache, H. Guo, B. Zhou, and X. Zeng, “The anisotropic Kerr nonlinear refractive index of the beta-barium borate (β-BaB2O4) nonlinear crystal,” Opt. Mater. Express 3(3), 357–382 (2013). M. Conforti and F. Baronio, “Extreme high-intensity and ultrabroadband interactions in anisotropic –β-BaB2O4 crystals,” J. Opt. Soc. Am. B 30(4), 1041–1047 (2013). G. I. Petrov, M. Zhi, D. Wang, and V. V. Yakovlev, “Nonresonant background suppression in coherent antiStokes Raman spectroscopy through cascaded nonlinear optical interactions,” Opt. Lett. 38(9), 1551–1553 (2013). D. N. Nikogosyan, “Basic nonlinear optical crystals,” in Nonlinear Optical Crystals, A Complete Survey, (Springer, 2005).

#197782 - $15.00 USD Received 17 Sep 2013; revised 18 Nov 2013; accepted 18 Nov 2013; published 17 Dec 2013 (C) 2013 OSA 30 December 2013 | Vol. 21, No. 26 | DOI:10.1364/OE.21.031960 | OPTICS EXPRESS 31960

17. J. D. Bierlein and H. Vanherzeele, “Potassium titanyl phosphate: properties and new applications,” J. Opt. Soc. Am. B 6(4), 622–633 (1989). 18. S. Sanna and W. G. Schmidt, “Lithium niobate X-cut, Y-cut, and Z-cut surfaces from ab initio theory,” Phys. Rev. B 81(21), 214116 (2010). 19. M. Bache and R. Schiek, “Review of measurements of Kerr nonlinearities in lithium niobate: the role of the delayed Raman response,” arXiv:1211.1721 [physics.optics]. 20. G. I. Petrov, V. V. Yakovlev, and N. I. Minkovski, “Broadband nonlinear optical conversion of a high-energy diode-pumped picosecond laser,” Opt. Commun. 229(1–6), 441–445 (2004). 21. R. Arora, G. I. Petrov, J. A. Liu, and V. V. Yakovlev, “Improving sensitivity in nonlinear Raman microspectroscopy imaging and sensing,” J. Biomed. Opt. 16(2), 021114 (2011). 22. http://www.sigmaaldrich.com/catalog/product/aldrich/w292907?lang=en®ion=US. 23. A. Bartasyte, V. Plausinaitiene, A. Abrutis, S. Stanionyte, S. Margueron, P. Boulet, T. Kobata, Y. Uesu, and J. J. Gleize, “Identification of LiNbO₃, LiNb₃O₈ and Li₃NbO₄ phases in thin films synthesized with different deposition techniques by means of XRD and Raman spectroscopy,” J. Phys. Condens. Matter 25(20), 205901 (2013).

1. Introduction Coherent anti-Stokes Raman scattering (CARS) spectroscopy and microscopy attract significant attention in that it allows label-free, chemically-selective and, potentially, sensitive imaging and sensing [1]. To achieve efficient nonlinear optical interaction, picosecond pulses are typically employed, since the spectral bandwidth of such pulses perfectly matches a typical linewidth for a Raman transition of a molecule in solution, i.e. a few wavenumbers. A growing number of applications requires simultaneous recording of a broadband CARS spectrum, especially, in the Raman fingerprint region spanning from 800 to 1800 cm−1, to achieve a comprehensive chemical assessment of the sample under study [2–5]. Those measurements are often difficult to perform because of the non-resonant instantaneous electronic four wave mixing (FWM) interaction which interferes with a resonant CARS signal generation and results in a complex spectral shape of the recorded spectrum. Various methods and techniques have been proposed and used extensively either to eliminate or to suppress the FWM background, thus increasing the specificity of the CARS spectroscopy. These techniques range from polarization control [6], temporal pulse shaping [7], heterodyning [8], and data processing [9, 10]. Each of those approaches has its own advantages and shortcomings, and the purpose of this report is to introduce yet another concept which utilizes the cascaded nonlinear optical interaction in χ ( 2 ) materials. In biological systems, collagenrich tissue can be considered as a representative example of such material. In noncentrosymmetric crystals, the cascaded quadratic nonlinearity under conditions of large phase mismatch is proportional to the phase mismatch factor Δk, where k is the wave vector [11]. It can be positive or negative depending on the phase mismatch. The material Kerr third-order nonlinearity is usually positive [12]. As a result, the effective total thirdorder nonlinearity can change its sign as one varies the phase matching angle. The cascaded quadratic nonlinearity and the third-order nonlinearity in nonlinear crystals have been studied extensively in the context of measuring the third-order nonlinear tensor elements [13, 17], soliton compression [11] and high-intensity third-harmonic generation [14], to name a few. We have recently proposed and experimentally validated a new technique for the FWM background suppression [15]. It is based on the interaction of nonlinear optical signals which are generated from the Kerr third-order nonlinear process and the cascaded quadratic process. In a typical CARS setup, where both the pump, ωp, and the Stokes, ωs, beams are focused into a nonlinear crystal, the nonlinearities from the electronic non-resonant Kerr effect, the resonant coherent Raman effect, and the cascaded quadratic processes coexist. In our early approach [15], the first process is the second-harmonic generation (SHG) of the pump beam which results in a signal at frequency 2 ωp. The second process is the difference-frequency generation (DFG) between the second harmonic of the pump beam, 2 ωp, and the Stokes beam, ωs, which leads to a new wave at frequency 2ωp- ωs, which is the same as the CARS signal frequency. We showed that by tuning the crystal angle, the cascaded second-order

#197782 - $15.00 USD Received 17 Sep 2013; revised 18 Nov 2013; accepted 18 Nov 2013; published 17 Dec 2013 (C) 2013 OSA 30 December 2013 | Vol. 21, No. 26 | DOI:10.1364/OE.21.031960 | OPTICS EXPRESS 31961

signal can be tuned out of phase with the non-resonant FWM background. This homodyne CARS process thus provides an alternative way of eliminating instantaneous FWM background. Unfortunately, the above scheme only works when the polarizations of the two beams (pump and Stokes) are perpendicular to the optical axis of a crystal, and the type I phase matching (oo → e) is employed. When the polarization of the pump and Stokes beams are both e-polarized, the ee → o interaction is highly phase mismatched. Therefore, the main cascaded channel would be ee → e interaction, which can never be phase matched. Consequently, there was no cascaded quadratic process observed, and the lineshape stayed unchanged as we varied the angle. In this report, we explore two of the four most widely used nonlinear optical crystals, potassium titanyl phosphate (KTP) [16, 17] and lithium niobate (LiNbO3) [18, 19]. Furthermore, we investigate the possibility of heterodyning CARS signal at the interface of two media – isopropyl alcohol and nonlinear crystal, LiNbO3. 2. Experimental setup The experimental setup is similar to the one used in the previous work [14]. Briefly, we employed a home-built MHz-rate diode-pumped Nd:YVO4 oscillator amplified by a diodepumped two-stage Nd:YVO4 amplifier, which produced 10 µJ, 8 ps pulses at the wavelength of 1064 nm and an average power as high as 8 W [20]. The output was split by a polarizing beam splitter (PBS). One part was focused into a single-mode GeO2 doped fiber to generate supercontinuum (SC) extending from 1100 nm to 1600 nm [21]. This supercontinuum radiation served as a broadband Stokes pulse (ωs), whereas the rest of the fundamental radiation (ωp) at 1064 nm was used as a narrow band (

Coherent anti-Stokes Raman spectroscopy utilizing phase mismatched cascaded quadratic optical interactions in nonlinear crystals.

We experimentally investigated the nonlinear optical interaction between the instantaneous four-wave mixing and the cascaded quadratic frequency conve...
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