Open Access
Add to BibSonomy
Abstract
We report on the synthesis of plasmonic Ag nanoparticles (NPs) embedded in a LiNbO3 crystal (AgNP:LN) by ion implantation and its application as an efficient broadband saturable absorber (SA) to realize Q-switched pulsed laser generation at both visible and near-infrared wavelength bands. The nonlinear optical response of AgNP:LN is considered as a synergistic effect between Ag NPs and LiNbO3. We apply the AgNP:LN as visible-near-infrared broadband saturable absorbers (SAs) into Pr:LuLiF4 bulk and Nd:YVO4 waveguide laser cavity, achieving efficient passively Q-switched laser at 639 nm and 1064 nm, respectively. This work paves a new way to tailor the nonlinear optical response of LiNbO3 crystals by using plasmonic Ag NPs, manifesting the significant potential as broadband SAs in the aspect of pulsed lasing.
© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement
1. Introduction
Lithium niobate (LiNbO3) is one of the most widely used multifunctional crystals with many unique features including archetypical electro-optic, acousto-optic, photorefractive, nonlinear optical, piezoelectric, and ferroelectric properties [1,2]. Many photonic structures including photonic nanowires, photonic crystal slabs, and microring resonators etc. have been constructed based on the platforms of ultrathin LiNbO3 films with thickness down to 100 nm [3–5]. LiNbO3 wafers or waveguides can be used as platforms for optical amplification or lasing [6,7], and high-speed electrooptic modulators, reaching tens of GHz bandwidth [8–11]. In addition, LiNbO3 chip can also integrate multi-components [12–15], e.g., as integrated quantum circuits [16]. Especially periodically poled LiNbO3 (PPLN) crystal, a new type of nonlinear optical crystal, has been demonstrated to own giant enhancement of frequency conversion efficiency in nonlinear optical applications when combined with noble nanoclusters [17]. In consequence, considering the nonlinear optical response of nanostructures, the realization of LiNbO3-based SAs and connecting with other components for constructing more complex devices and various applications (e.g., off-free gigahertz mid-infrared frequency comb and double Q-switched laser) have significant potential [18,19]. It is urgently essential to fabricate efficient LiNbO3-based SAs with superior saturable absorption properties by breaking through the barrier of the two-photon absorption of LiNbO3.
Metallic NPs have attracted tremendous attentions of researchers in a variety of areas owing to their large third-order optical nonlinearities attributed to the localized surface plasmon resonance (LSPR) influenced by the size or shape of NPs and surrounding medium [20–24]. Particularly, noble-metal NPs (e.g., Au or Ag) play a crucial role in the applications of biosensing, imaging, diagnostic/therapy, and photocatalysts [25,26]. Among of these applications, Q-switched or mode-locked laser based on NPs (nanospheres, nanorods or nanopyramids) as efficient SAs has achieved great progress in the last few years [27–31]. For example, the gold nanorods produced by chemical synthesis have been applied as SAs and generated ultrafast laser pulses in bulk or fiber laser systems [31]. It is deserved to expect the efficient modification of substrate by noble metal NPs. However, superficial NPs fabricated by chemical synthesis have limitations on modifying the optical properties of substrate compared with embedded NPs in functional crystals. Since the pioneering work reported by Davenas et al. in 1973 [32], ion implantation has opened a promising avenue to modify the optical properties of dielectric materials by embedded NPs with kinds of shapes induced by ion irradiation [33–39]. It has been reported that the dielectric environment of NPs could have significant contribution to the optical properties of NPs, and the multifunctional dielectric crystals combined with NPs could expand the application in photonic devices [40,41]. Based on the optical properties of nanocomposite, superior laser performances have been realized in waveguide structure by designing the monolithic laser resonator including waveguiding structures or saturable absorbers in a desirable way [41]. Compared with bulk laser systems, waveguide laser shows lower lasing threshold and higher slope efficiency due to confinement of small waveguide volume, in which higher optical intensities could be reached in respect to the bulks [42–52]. In general, SAs used to generate pulsed laser include colored glasses [53], semiconductor saturable absorber mirrors (SESAMs) [54], and nanomaterials (i.e., quantum dots [55], carbon nanotubes [56], and two-dimensional materials [57,58]). For example, Bao et al. reported on the ultrafast pulse generation using atomic-layer graphene based SA, opening up the application of graphene in optical communications [59]. Additional SAs deserve further exploration to develop sophisticated devices, which has significance in pulsed lasing and photonics. With the development of nanomaterial and nanotechnology, saturable absorption of NPs has attracted a vast amount of research effort to be used as SA in pulsed laser generation. The rapid development of nanoscience and nanotechnology, a growing number of NPs have been shown to possess remarkable saturable absorption, which attract researchers’ attention to use them as SAs. Recently, stable laser pulses at 639 nm (within the main LSPR band) have been achieved by using Nd:YAG wafer with embedded Au NPs as a saturable absorber and Pr:LuLiF4 crystal as gain medium [60]. More recently, we reported on the synthesis of Au embedded in LiNbO3 crystal (AuNP:LN) as a SA for 1-μm-wavelength Q-switched mode-locked laser generation owing to the efficient saturable absorption of AuNP:LN at near-infrared (NIR) wavelength [41]. Nevertheless, AuNP:LN does not show obvious saturable absorption at visible wavelength band due to the dominate of two-photon absorption of LiNbO3, limiting the possibility of AuNP:LN as a SA for the generation of visible pulse laser. Compared with Au NPs, Ag NPs synthesized by ion implantation have smaller diameters and higher volume fraction under the same circumstance, which can influence the linear optical response and third-order nonlinear optical response. In this work, we introduce Ag NPs to tailor the third-order optical nonlinearities of LiNbO3 at visible and near-infrared band based on superior SPR properties of Ag NPs. The nonlinear optical response measured by the Z-scan system with femtosecond pulses at 515 nm and 1030 nm can be seen as a synergistic effect between Ag NPs and substrate LiNbO3, which can be analyzed by a two-layer model. Finally, utilizing the broadband saturable absorption of Ag NPs, the visible and near-infrared Q-switched pulsed lasers at 639 nm and 1064 nm are implemented with AgNP:LN as a broadband SA, respectively, manifesting significant potential of LiNbO3 in the aspect of pulsed lasing and photonics by using embedded metallic nanoparticles.
2. Experimental
2.1 Sample preparation
The LiNbO3 used in this work was cut into wafers of dimensions of 10 (x) mm × 10 (y) mm × 1 (z) mm and was optically polished. Samples 1-4 were synthesized by Ag+ ions implanted into LiNbO3 by analytical-type ion-implanter LC22-100-01 at fluences of 1 × 1016 ions/cm2, 3 × 1016 ions/cm2, 5 × 1016 ions/cm2, and 1 × 1017 ions/cm2, respectively. The energy of Ag+ ions was 200 keV. The longitudinal straggle calculated by SRIM (Stopping and Ranges of Ions in Matter) code is 215 Å. The Ag+ ion implantation was performed along the normal direction of the sample surface. The schematic diagram of Ag+ ion implantation process can be seen in insert of Fig. 1. After these processes, samples were produced.
Fig. 1 The experimental setup of the open and closed aperture Z-scan system. Insert is schematic diagram of Ag+ ion implantation process.
2.2 Characterization of Ag NPs
The TEM measurements were performed by FEI Tecnai G2 F20 S-TWIN operated at an accelerating voltage of 200 kV. The optical absorption spectra of the implanted specimens were measured in a wavelength range from 350 nm to 1100 nm by UV-VIS-NIR spectrophotometer (Hitachi, U-4100).
2.3 Z-scan measurement
Z-scan system was utilized to investigate the saturable absorption performance of samples, and the schematic of the experimental arrangement of the device is depicted in Fig. 1. The Z-scan experiment was performed by using femtosecond pulsed laser at 515 nm and 1030 nm, with a repetition rate of 100 Hz and a pulse with of 340 fs. As shown, as the sample moves along the laser propagation direction gradually and traverses the focus of laser with a focal length of 150 mm, transmittance of the sample was measured as a function of the position of sample.
2.4 Visible Q-switched laser operation
The arrangement of pulsed laser experiment is shown in Fig. 2. As the pump source, a laser diode with the emission wavelength of 445 nm was focused into laser cavity by a lens with a focal length of 25 mm. The laser cavity is plane-concave formed by a pair of mirroes (M1 and M2). The input mirror M1 was a plane mirror with an antireflection coating for the pump wavelength (445 nm) at the side of the pump light and highly reflective coating for the laser wavelength (639 nm) at the side of intracavity. The output mirror M2 was a concave output coupler with the transmittance of 1.8% at 639 nm. The Pr:LuLiF4 crystal with dimensions of 6 (x) mm × 10 (y) mm × 2 (z) mm was wrapped by an indium foil and mounted in a copper block cooled by the circular water with temperature of 7 °C to remove the heat generated during the laser process. The Sample 2 (AgNP:LN with fluence of 3 × 1016 ions/cm2) as a SA was placed between the end-face of the Pr:LuLiF4 and the output couplers M2. The Q-switched laser output power was measured by a powermeter (1918-R, Newport, Inc.) and the pulsed output performance including the pulse duration and repetition rate was detected by a digital oscilloscope combined with a silicon detector at the end of experimental system.
2.5 1 μm Q-switched pulsed lasing generation
The experiment was performed by the end-face coupling arrangement with a linearly polarized light beam at 808 nm, generated from a tunable CW Ti:sapphire (Coherent MBR-PE) laser, as the optical pump beam. Subsequently, a spherical convex lens with a focal length of 30 mm was utilized to converge and couple the pump laser into a laser-written Nd:YVO4 waveguide platform, which was clamped closely by the input mirror (with high transmission of 98% at 808 nm and high reflectivity > 99% at 1064 nm) and the ion injection face of sample. In this case, Sample 4 (AgNP:LN with fluence of 1 × 1017 ions/cm2) as a SA. A digital oscilloscope (Tektronix, MSO72504DX) was located after objective lens to display the image of pulsed laser from the output face of the waveguide.
3. Results and discussion
Transmission electronic microscopy (TEM) has been applied to investigate the microscopic structures of AgNP:LN. Figures 3(a)-3(d) show the cross-sectional transmission electronic microscopy (XTEM) micrographs of the Samples 1-4, where Ag NPs are located near the surface of crystal at a total range of around 120 nm, which are consistent with the simulation results by the code of SRIM shown in Fig. 4(a). Corresponding distributions of NPs’ diameters are displayed in Figs. 3(e)-3(h). As shown, with the increase of ions fluence, the average diameters of NPs grow from 1.24 nm to 3.61 nm. The average size and deviation of NPs at different fluence can been seen in Fig. 4(b). As illustrated in the inserts of Figs. 3(a)-3(d), the polymorphic state of implanted region is indicated by fast Fourier transformation (FFT) pattern. In order to obtain further information of Ag NPs, high-resolution transmission electron microscopy (HRTEM) is utilized to image details of NPs as shown in Figs. 3(i)-3(l). It is obvious that NPs with higher fluence own larger size. The interplanar spacing d of single NP is calculated to be 0.23 nm as shown in upper inserts, which is well assigned to crystal orientation (111) of Ag from standard data card (PDF#65-8428). Besides, compared with the results of TEM images in Figs. 3(a)-3(d), the HRTEM images show the prior crystallization of Ag NPs which can also be indicated by FFT analysis of single Ag NP (lower inserts in Figs. 3(i)-3(l)). To obtain the more accurate analysis, the images of selected area electron diffraction (SAED) of implanted region and single NP are carried out as shown in Figs. 3(m) and 3(n) (Sample 2) and Figs. 3(o) and 3(p) (Sample 4), respectively. As we can see, the SAED of single NP shows prior crystallization compared with that of implanted region, which is agreed with the conclusion above, and the higher fluence leads to a superior crystallization as well. The element mappings of Samples 1-4 are shown in Figs. 3(q)-3(t), respectively, which further confirms the formation of Ag NPs in the LiNbO3 crystal. Element mapping can directly display the variation of diameters of nanoparticles at different fluence. As shown in Figs. 3(q)-3(t), diameter of nanoparticles grows as implantation fluence increases.
Fig. 3 (a-d) XTEM images of samples 1-4. Upper inserts are the diameter distributions of NPs obtained from the XTEM images. Lower inserts are FFT images of implanted regions. (e-h) HRTEM images of Samples 1-4. Upper inserts show interplanar spacing d of single NP. Lower inserts are FFT analysis of single Ag NP. SAED of implanted region (i,k) and single NP (j,l) of Sample 2 and Sample 4. (m-p) Element Mappings of Samples 1-4.
Fig. 4 (a) Ag+ ion distribution simulated by the SRIM code. (b) Mean and the deviation of the NPs vs fluence
After the basic characterization of the prepared Ag NPs, the linear optical responses of AgNP:LN are investigated. Figure 5(a) depicts the absorption spectra of samples. As shown, the absorption peaks of Samples 1-4 are located at 470, 494, 508 and 529 nm, respectively. The reason for the red shift in the absorption peak is that NPs with a larger scale are synthesized with higher ions fluence. The absorption spectrum can be calculated by Mie theory:
where and are the complex dielectric constants of metal and insulator, respectively. p is the volume fraction of metal (p = 0.1). and denote the imaginary part of and the wavelength of light in vacuum, respectively [61]. The results of calculation are shown in Fig. 5(b), which agree with the measurement results on the positions of absorption peaks and variation trends. Figure 5(c) shows the measured transmission spectra of samples. As shown, transmittance declines as ions fluence increases. Obviously, Sample 4 seems an opaque at visible wavelength band.Fig. 5 (a) Measured absorption spectra of AgNP:LN with different fluences. (b) Absorption spectra calculated by Mie theory. (c) Measured transmission spectra of samples.
Compared with the linear optical response of AgNP:LN, the nonlinear optical response is more attractive due to its wide applications in photonic devices. However, the nonlinear optical responses of AgNP:LN, especially the synergistic effect, are lacking detailed investigation in the previous reports due to the complex interaction between NPs and dielectric crystals. To gain further insight into AgNP:LN, the nonlinear optical responses are investigated by Z-scan technique with closed-aperture and open-aperture. Figures 6(a) and 6(b) show the closed-aperture Z-scan measurement and corresponding theoretical fitting (solid lines) of pure LiNbO3 and Sample 2 at energy of 100 nJ, 150 nJ, 200 nJ, respectively. As the energy increases, the nonlinearity phenomenon is more obvious. Figure 6(c) shows the results of Z-scan of Samples 1-4 at 150 nJ, and corresponding values of nonlinear refractive index n2 are calculated by equation:
where , , , , is the distance along the laser propagation direction, is the beam’s diffraction length, is the linear absorption coefficient, is the effective thickness of the Ag NPs layer, is the Ag NPs layer thickness [62]. It is convincing that our results show the same orders of magnitude with prior results [63], although cascaded quadratic nonlinearities and delayed Raman response are excepted in our calculation. The displacement per atom (DPA) calculated by the SRIM software is shown in insert. As we can see, with the increase of fluence, the DPA is enhanced, which means the lattice damage will increase as the depth increases. Among these samples, Sample 4 has the largest DPA while Sample 1 has the lowest DPA. That is to say, the lattice damage increases with the increase of fluence. And the lattice damage may lead to the decrease of n2. Therefore, we can draw to a conclusion that crystal lattice damage becomes more severe with fluence increasing, which results in the degradation of n2. With a standard deviation less than 2.02 × 10−16, the fitting results of n2 are shown in Fig. 6(d), which indicates there is a threshold of ions fluence on nonlinear refraction index n2. At first, n2 decreases significantly with the increase of ions fluence, dropping to the lowest point. However, after the threshold, n2 rises dramatically to reach the highest point. The nonlinearity can be seen a result of competition between enhancement effect of synthesized NPs and damage of crystal lattice caused by ion implantation. At low range of ions fluence, as the fluence increases, the effect of the NPs on the enhancement of nonlinear refractive index become strong, but the influence of the lattice damage on decrease of the nonlinear refractive index is more serious. As fluence increases, the LSPR of NPs will have a stronger effect on the enhancement of nonlinear refractive index [64,65]. In other word, the contribution of NPs is strengthen compared with the damage caused by ion implantation at this case.Fig. 6 Results of closed-aperture Z-scan at excitation of 515 nm. Closed-aperture measurements and fitting results of (a) pure LiNbO3 and (b) Sample 2 at different energies. (c) Closed-aperture measured results and fitting results of Samples 1-4 at 150 nJ, and corresponding nonlinear refractive index is shown in (d). Insert is the displacement per atom (DPA) calculated by the SRIM software.
Considering the saturable absorption property of metal NPs, the nonlinear absorption of pure LiNbO3 and AgNP:LN is investigated, respectively. As shown in Fig. 7(a), it is obvious that pure LiNbO3 crystal demonstrates strong two-photon absorption response in Z-scan measurements with an open aperture at energy of 100 nJ, 150 nJ and 200 nJ. The nonlinear absorption coefficient β can be obtained by fitting the open-aperture Z-scan results using Eq. (3):
where is the excitation intensity, is the distance along the laser propagation direction, is the linear absorption coefficient, β is the nonlinear absorption coefficient. This equation can be solved as follows:where , is the light intensity at the focus, is the effective thickness of the pure LiNbO3, is the beam’s diffraction length., is the thickness of LiNbO3 [66]. The fitting results (error of approximately ± 10%) are shown in Table 1. For Ag implanted samples, the nonlinear optical responses are complex because of the synergistic effect between Ag NPs and LiNbO3. Here, Sample 2 is employed as a typical example. As seen in Fig. 7(b), as the sample moves to the focus of laser, the transmittance increases slightly with the increase of the incident energy, whereafter, it decreases significantly. Although it is common in some cases of nonlinear optical materials, the situation is quite different in our case [67]. For one thing, the nonlinear optical responses of LiNbO3 substrate show a non-ignorable effect during the process of the measurement of AgNP:LN. For another thing, the thickness between substrate and NPs has a huge difference which makes it cannot be seen as a single nonlinear material. Based on the above considerations, we proposed a simple model with two layers of opposite nonlinear optical responses. Without considering the interaction between the nanoparticle layer and the substrate, the nonlinear optical response of AgNP:LN can be seen a synergic effect between the saturable absorption of Ag NPs and two-photon absorption of LiNbO3 substrate. On account of this model, the measured nonlinear optical response results can be divided into two curves which represent the nonlinear properties of Ag NPs and LiNbO3 substrate (Fig. 7(c)), respectively. It becomes easier to investigate the nonlinear optical response of embedded NPs in LiNbO3 crystal. In general, the saturation intensity can be obtained by fitting the nonlinear optical response curve with equation:where is the saturation intensity [68]. As shown in Table 1, is calculated to be 48.04 GW/cm2 at different energies, which indicates the significant potential in photonic devices. In addition, the nonlinear absorption coefficient βeff of LiNbO3 in AgNP:LN can also be obtained utilizing the Eqs. (3) and (4), which is shown in Table 1. Comparing to the normalized transmittance of pure LiNbO3 in Fig. 7(a), the third-order nonlinear optical response of substrate in AgNP:LN shown in Fig. 7(b) weakens, which is due to the absorption of Ag NPs and the decrease of light intensity on substrate. In order to reveal the process of analysis more clearly, Figs. 7(d)-7(f) show the separation of nonlinear response of Sample 2 at energy of 100 nJ, 150 nJ, 200 nJ, respectively. The dotted lines represent the saturable absorption of Ag NPs and corresponding two-photon absorption of substrate, separately. In addition to the superior nonlinear optical response of Sample 2, broadband saturable absorption of Ag NPs can be expected by increasing the ions fluences for the pulsed laser generation. The open-aperture Z-scan experiment was carried out and Fig. 8(a) shows the variation of the nonlinear transmittance with the increase of implanted fluence under pulse energy of 100 nJ. As shown, there is only a valley when the fluence is 1 × 1016 ions/cm2, indicating the dominant role of two-photon absorption of substrate. As fluence increases, peak appears owing to the dominant effect of saturable absorption of Ag NPs. With the increase of implantation fluence, the nonlinearity of the sample increases. However, the transmittance of the sample decreases with the increase of ions fluence as illustrated in Fig. 5(c). When the fluence is up to 1 × 1017 ions/cm2 (Sample 4), even though it has large nonlinearity but it is not suitable as a saturable absorber to generate pulsed laser, because Sample 4 is almost an opaque at the visible wavelength band. In addition, the transmittance of Sample 3 is also not high, and the laser performance is not good. Hence, after several times’ attempts, it has been proved that Sample 2 possesses the suitable nonlinear properties and transmittance and it is suitable as a SA for pulsed laser generation.Fig. 7 (a) Measured and fitting results of nonlinear transmittance of pure LiNbO3 at different energies. (b) Measured results of Sample 2 at 100 nJ, 150 nJ, 200 nJ. (c) Divided saturable absorption peaks of Ag NPs and two-photon absorption of LiNbO3 substrate from Sample 2 at 100 nJ, 150 nJ, 200 nJ. Separation of the results of open-aperture Z-scan of Sample 2 at energy of (d) 100 nJ, (e) 150 nJ, (f) 200 nJ.
Table 1. Nonlinear parameters at different pulse energies.
Fig. 8 (a) Results of open-aperture Z-scan of samples with different fluences at 100 nJ. (b) The output power of 639 nm Q-switched laser as a function of launched power. (c) Emission spectrum at 639nm. Insert shows the typical pulse train.
Corresponding characterization of Q-switched pulsed lasing is shown in Figs. 8(b) and 8(c). Figure 8(b) shows the average output power as a function of incident power. As the incident power increases linearly to the maximum of 938 mW, the output power reaches the maximum value of 6.48 mW, with the threshold of 756 mW and slope efficiency of 3.8%. Figure 8(c) manifests the central wavelength of the pulsed laser is 639 nm, which corresponds to the emission line of Pr3+ ion fluorescence transition band 3P0→3F2. Insert depicts the typical pulse train of the Q-switched pulsed lasing. The minimum of pulse duration is 0.963 μs, and maximum repetition rate is 137 kHz.
Although the transmittance of samples is low at the visible wavelength band, the transmittance is high at near-infrared. Figures 9(a) and 9(b) show the open-aperture Z-scan results of Samples 1-4 at 1030 nm under the pulse energy of 90 nJ. Tailoring of optical nonlinearities of LiNbO3 crystals can be further achieved by using different fluences of implanted Ag ions. As shown in Fig. 9(a), as the implanted ions are at a low range of fluence (Samples 1-3), there is no obvious saturable nonlinearity. However, as the fluence is up to 1 × 1017 ions/cm2 (Sample 4), the saturable absorption appears, as shown in Fig. 9(b). A stable Q-switched pulsed laser at wavelength of 1064 nm has been implemented by using Sample 4 as a SA into a laser-written Nd:YVO4 waveguide system with the excitation of 808 nm [69]. Figure 9(c) shows the average output power as a function of incident power. The maximum output power is up to 288.57 mW and the lasing threshold is 161.84 mW. The slope efficiency is 31.51%. In a waveguide, the pump and laser modes are tightly confined within the waveguide core, facilitating a lower lasing threshold and improved slope efficiency, which are critical parameters in solid state laser systems [44,70]. Figure 9(d) indicates that the central wavelength of the pulsed laser is 1064 nm, which corresponds to the transition 4F3/2→4I11/2 of Nd3+ ions. Insert displays the typical pulse train of the Q-switched pulsed laser. In comparison with the systems based on Au NPs embedded LiNbO3 SA, the 1 μm Q-switched waveguide laser based on AgNP:LN SA exhibits better performance [41]. More specifically, for TE polarized lasing, under the same pump power (e.g. 550 mW), the 1 μm Q-switched waveguide laser based on AgNP:LN SA possesses much higher output power (~175 mW), peak power (~600 mW), and pulse energy (~38 nJ), which is superior to the similar system based on the SA of Au NPs embedded LiNbO3, in which the output power (~60 mW), peak power (~140 mW), and pulse energy (~7.5 nJ) are considerably lower. This may be partly due to the higher fluence of Ag ions and the saturation intensity modification from the higher-concentration Ag NPs. This work has expanded the applications of LiNbO3 with NPs as a broadband saturable absorber in the aspect of pulsed lasing and photonics.
Fig. 9 Open-aperture Z-scan results of (a) Samples 1-3 and (b) Sample 4 under 340 fs at 1030 nm. (c) The output power as a function of launched power of Q-switched pulsed laser. (d) Emission spectrum at 1064 nm. Insert shows the typical pulse train.
4. Conclusions
In conclusion, we report on the synthesis of Ag NPs embedded in LiNbO3 by using direct Ag ion implantation. The nonlinear optical response of the AgNP:LN system has been investigated by Z-scan technique and analyzed by the tailoring of the optical nonlinearity of LiNbO3. The broadband saturable absorption response of the AgNP:LN is demonstrated to be a synergistic effect between Ag NPs and substrate. Finally, Q-switched pulsed lasers at both 639 nm and 1064 nm have been implanted by using AgNP:LN as broadband SAs in Pr:LuLiF4 and Nd:YVO4 crystal, achieving the modulation of laser wavelength band by the fluence of implantation ions. This work not only opens a new way to analyze complex nonlinear optical response, but also achieves the tailoring of optical nonlinearities of LiNbO3 crystals by implanting different fluence of Ag ions. The results of Q-switched laser also manifest the significant potential of LiNbO3 with NPs as broadband saturable absorber in the aspect of pulsed lasing and photonics.
Funding
National Natural Science Foundation of China (NSFC) (11535008; 61522510); STCSM Excellent Academic Leader of Shanghai (17XD1403900).
References
1. K. Lengyel, Á. Péter, L. Kovács, G. Corradi, L. Pálfalvi, J. Hebling, M. Unferdorben, G. Dravecz, I. Hajdara, Z. Szaller, and K. Polgár, “Growth, defect structure, and THz application of stoichiometric lithium niobate,” Appl. Phys. Rev. 2(4), 040601 (2015). [CrossRef]
2. C. Paillard, X. Bai, I. C. Infante, M. Guennou, G. Geneste, M. Alexe, J. Kreisel, and B. Dkhil, “Photovoltaics with ferroelectrics: current status, and beyond,” Adv. Mater. 28(26), 5153–5168 (2016). [CrossRef] [PubMed]
3. A. Bartasyte, S. Margueron, T. Baron, S. Oliveri, and P. Boulet, “Toward high-quality epitaxial LiNbO3 and LiTaO3 thin films for acoustic and optical applications,” Adv. Mater. Interfaces 4(8), 1600998 (2017). [CrossRef]
4. G. Poberaj, H. Hu, W. Sohler, and P. Günter, “Lithium niobate on insulator (LNOI) for micro-photonic devices,” Laser Photonics Rev. 6(4), 488–503 (2012). [CrossRef]
5. J. Chiles and S. Fathpour, “Mid-infrared integrated waveguide modulators based on silicon-on-lithium-niobate photonics,” Optica 1(5), 350 (2014). [CrossRef]
6. D. Brüske, S. Suntsov, C. E. Rüter, and D. Kip, “Efficient ridge waveguide amplifiers and lasers in Er-doped lithium niobate by optical grade dicing and three-side Er and Ti in-diffusion,” Opt. Express 25(23), 29374–29379 (2017). [CrossRef]
7. D. Z. Wang, D. H. Sun, X. L. Kang, Y. H. Sang, B. X. Yan, H. Liu, and Y. Bi, “Periodically poled self-frequency-doubling green laser fabricated from Nd:Mg:LiNbO3 single crystal,” Opt. Express 23(14), 17727–17738 (2015). [CrossRef] [PubMed]
8. A. J. Mercante, P. Yao, S. Shi, G. Schneider, J. Murakowski, and D. W. Prather, “110 GHz CMOS compatible thin film LiNbO3 modulator on silicon,” Opt. Express 24(14), 15590–15595 (2016). [CrossRef] [PubMed]
9. J. Macario, P. Yao, S. Shi, A. Zablocki, C. Harrity, R. D. Martin, C. A. Schuetz, and D. W. Prather, “Full spectrum millimeter-wave modulation,” Opt. Express 20(21), 23623–23629 (2012). [CrossRef] [PubMed]
10. A. Rao and S. Fathpour, “Compact lithium niobate electrooptic modulators,” IEEE J. Sel. Top. Quantum Electron. 24(4), 3400114 (2018). [CrossRef]
11. A. Rao, A. Patil, P. Rabiei, A. Honardoost, R. DeSalvo, A. Paolella, and S. Fathpour, “High-performance and linear thin-film lithium niobate Mach-Zehnder modulators on silicon up to 50 GHz,” Opt. Lett. 41(24), 5700–5703 (2016). [CrossRef] [PubMed]
12. J. Thomas, M. Heinrich, P. Zeil, V. Hilbert, K. Rademaker, R. Riedel, S. Ringleb, C. Dubs, J.-P. Ruske, S. Nolte, and A. Tünnermann, “Laser direct writing: Enabling monolithic and hybrid integrated solutions on the lithium niobate platform,” Phys. Status Solidi., A Appl. Mater. Sci. 208(2), 276–283 (2011). [CrossRef]
13. A. Sergeyev, R. Geiss, A. S. Solntsev, A. A. Sukhorukov, F. Schrempel, T. Pertsch, and R. Grange, “Enhancing guided second-harmonic light in lithium niobate nanowires,” ACS Photonics 2(6), 687–691 (2015). [CrossRef]
14. E. Saglamyurek, N. Sinclair, J. Jin, J. A. Slater, D. Oblak, F. Bussières, M. George, R. Ricken, W. Sohler, and W. Tittel, “Broadband waveguide quantum memory for entangled photons,” Nature 469(7331), 512–515 (2011). [CrossRef] [PubMed]
15. A. S. Solntsev, T. Liu, A. Boes, T. G. Nguyen, C. W. Wu, F. Setzpfandt, A. Mitchell, D. N. Neshev, and A. A. Sukhorukov, “Towards on-chip photon-pair bell tests: Spatial pump filtering in a LiNbO3 adiabatic coupler,” Appl. Phys. Lett. 111(26), 261108 (2017). [CrossRef]
16. H. Jin, F. M. Liu, P. Xu, J. L. Xia, M. L. Zhong, Y. Yuan, J. W. Zhou, Y. X. Gong, W. Wang, and S. N. Zhu, “On-chip generation and manipulation of entangled photons based on reconfigurable lithium-niobate waveguide circuits,” Phys. Rev. Lett. 113(10), 103601 (2014). [CrossRef] [PubMed]
17. E. Yraola, P. Molina, J. L. Plaza, M. O. Ramírez, and L. E. Bausá, “Spontaneous emission and nonlinear response enhancement by silver nanoparticles in a Nd3+-doped periodically poled LiNbO3 laser crystal,” Adv. Mater. 25(6), 910–915 (2013). [CrossRef] [PubMed]
18. Y. Sun, Y. Bai, D. Li, L. Hou, B. Bai, Y. Gong, L. Yu, and J. Bai, “946 nm Nd: YAG double Q-switched laser based on monolayer WSe2 saturable absorber,” Opt. Express 25(18), 21037–21048 (2017). [CrossRef] [PubMed]
19. A. S. Mayer, C. R. Phillips, C. Langrock, A. Klenner, A. R. Johnson, K. Luke, Y. Okawachi, M. Lipson, A. L. Gaeta, M. M. Fejer, and U. Keller, “Offset-free gigahertz midinfrared frequency comb based on optical parametric amplification in a periodically poled lithium niobate waveguide,” Phys. Rev. Appl. 6(5), 054009 (2016). [CrossRef]
20. L. Novotny and N. Van Hulst, “Antennas for light,” Nat. Photonics 5(2), 83–90 (2011). [CrossRef]
21. J. M. Lee, J. Lim, N. Lee, H. I. Park, K. E. Lee, T. Jeon, S. A. Nam, J. Kim, J. Shin, and S. O. Kim, “Synergistic concurrent enhancement of charge generation, dissociation, and transport in organic solar cells with plasmonic metal-carbon nanotube hybrids,” Adv. Mater. 27(9), 1519–1525 (2015). [CrossRef] [PubMed]
22. X. Lan and Q. Wang, “Self-assembly of chiral plasmonic nanostructures,” Adv. Mater. 28(47), 10499–10507 (2016). [CrossRef] [PubMed]
23. N. J. Halas, S. Lal, S. Link, W. S. Chang, D. Natelson, J. H. Hafner, and P. Nordlander, “A plethora of plasmonics from the laboratory for nanophotonics at rice university,” Adv. Mater. 24(36), 4842–4877 (2012). [CrossRef] [PubMed]
24. H. Chen, L. Shao, Q. Li, and J. Wang, “Gold nanorods and their plasmonic properties,” Chem. Soc. Rev. 42(7), 2679–2724 (2013). [CrossRef] [PubMed]
25. P. A. Hernley, S. A. Chavez, J. P. Quinn, and S. Linic, “Engineering the optical and catalytic properties of co-catalyst/semiconductor photocatalysts,” ACS Photonics 4(4), 979–985 (2017). [CrossRef]
26. S. Sarina, E. R. Waclawik, and H. Zhu, “Photocatalysis on supported gold and silver nanoparticles under ultraviolet and visible light irradiation,” Green Chem. 15(7), 1814 (2013). [CrossRef]
27. X. Liu, Q. Guo, and J. Qiu, “Emerging low-dimensional materials for nonlinear optics and ultrafast photonics,” Adv. Mater. 29(14), 1605886 (2017). [CrossRef] [PubMed]
28. S. Wang, Y. Zhang, J. Xing, X. Liu, H. Yu, A. D. Lieto, M. Tonelli, T. C. Sum, H. Zhang, and Q. Xiong, “Nonlinear optical response of Au nanorods for broadband pulse modulation in bulk visible lasers,” Appl. Phys. Lett. 107(16), 161103 (2015). [CrossRef]
29. D. Wu, J. Peng, Z. Cai, J. Weng, Z. Luo, N. Chen, and H. Xu, “Gold nanoparticles as a saturable absorber for visible 635 nm Q-switched pulse generation,” Opt. Express 23(18), 24071–24076 (2015). [CrossRef] [PubMed]
30. Y. H. Lin, S. F. Lin, Y. C. Chi, C. L. Wu, C. H. Cheng, W. H. Tseng, J. H. He, C. I. Wu, C. K. Lee, and G. R. Lin, “Using n- and p-type Bi2Te3 topological insulator nanoparticles to enable controlled femtosecond mode-locking of fiber lasers,” ACS Photonics 2(4), 481–490 (2015). [CrossRef]
31. X. Wang, Z. Luo, H. Liu, M. Liu, A. Luon, and W. Xu, “Microfiber-based gold nanorods as saturable absorber for femtosecond pulse generation in a fiber laser,” Appl. Phys. Lett. 105(16), 161107 (2014). [CrossRef]
32. J. Davenas, A. Perez, P. Thevenard, and C. H. S. Dupuy, “Correlation between absorption bands and implanted alkali ions in LiF,” Phys. Status Solidi 19(2), 679–686 (1973). [CrossRef]
33. H. S. Alkhaldi, F. Kremer, P. Mota-Santiago, A. Nadzri, D. Schauries, N. Kirby, M. C. Ridgway, and P. Kluth, “Morphology of ion irradiation induced nano-porous structures in Ge and Si1-xGex,” J. Appl. Phys. 121(11), 115705 (2017). [CrossRef]
34. X. Ou and S. Facsko, “Crystalline nanostructures on Ge surfaces induced by ion irradiation,” Nucl. Instrum. Meth. B 341, 13–16 (2014). [CrossRef]
35. M. C. Ridgway, R. Giulian, D. J. Sprouster, P. Kluth, L. L. Araujo, D. J. Llewellyn, A. P. Byrne, F. Kremer, P. F. P. Fichtner, G. Rizza, H. Amekura, and M. Toulemonde, “Role of thermodynamics in the shape transformation of embedded metal nanoparticles induced by swift heavy-ion irradiation,” Phys. Rev. Lett. 106(9), 095505 (2011). [CrossRef] [PubMed]
36. P. Mota-Santiago, F. Kremer, A. Nadzri, M. C. Ridgway, and P. Kluth, “Elongation of metallic nanoparticles at the interface of silicon dioxide and silicon nitride,” Nucl. Instrum. Meth. B 409, 328–332 (2017). [CrossRef]
37. S. Wolf, J. Rensberg, A. Johannes, R. Thomae, F. Smit, R. Neveling, M. Moodley, T. Bierschenk, M. Rodriguez, B. Afra, S. Bin Hasan, C. Rockstuhl, M. Ridgway, K. Bharuth-Ram, and C. Ronning, “Shape manipulation of ion irradiated Ag nanoparticles embedded in lithium niobate,” Nanotechnology 27(14), 145202 (2016). [CrossRef] [PubMed]
38. X. Ou, R. Kögler, X. Wei, A. Mücklich, X. Wang, W. Skorupa, and S. Facsko, “Fabrication of horizontal silicon nanowire arrays on insulator by ion irradiation,” AIP Adv. 1(4), 042174 (2011). [CrossRef]
39. Z. Li and F. Chen, “Ion beam modification of two-dimensional materials: Characterization, properties, and applications,” Appl. Phys. Rev. 4(1), 011103 (2017). [CrossRef]
40. A. L. Stepanov, “Nonlinear optical properties of implanted metal nanoparticles in various transparent matrixes: a review,” Rev. Adv. Mater. Sci. 27(2), 115–145 (2011).
41. C. Pang, R. Li, Z. Li, N. Dong, C. Cheng, W. Nie, R. Böttger, S. Zhou, J. Wang, and F. Chen, “Lithium niobate crystal with embedded au nanoparticles: a new saturable absorber for efficient mode-locking of ultrafast laser pulses at 1 µm,” Adv. Opt. Mater. 6(16), 1800357 (2018). [CrossRef]
42. C. Grivas, “Optically pumped planar waveguide lasers, Part I: fundamentals and fabrication techniques,” Prog. Quantum Electron. 35(6), 159–239 (2011). [CrossRef]
43. S. Hakobyan, V. J. Wittwer, K. Hasse, C. Kränkel, T. Südmeyer, and T. Calmano, “Highly efficient Q-switched Yb:YAG channel waveguide laser with 5.6 W of average output power,” Opt. Lett. 41(20), 4715–4718 (2016). [CrossRef] [PubMed]
44. R. Mary, G. Brown, S. J. Beecher, F. Torrisi, S. Milana, D. Popa, T. Hasan, Z. Sun, E. Lidorikis, S. Ohara, A. C. Ferrari, and A. K. Kar, “1.5 GHz picosecond pulse generation from a monolithic waveguide laser with a graphene-film saturable output coupler,” Opt. Express 21(7), 7943–7950 (2013). [CrossRef] [PubMed]
45. G. Salamu, F. Jipa, M. Zamfirescu, and N. Pavel, “Laser emission from diode-pumped Nd:YAG ceramic waveguide lasers realized by direct femtosecond-laser writing technique,” Opt. Express 22(5), 5177–5182 (2014). [CrossRef] [PubMed]
46. Z. Li, Y. Zhang, C. Cheng, H. Yu, and F. Chen, “6.5 GHz Q-switched mode-locked waveguide lasers based on two-dimensional materials as saturable absorbers,” Opt. Express 26(9), 11321–11330 (2018). [CrossRef] [PubMed]
47. G. Palmer, S. Gross, A. Fuerbach, D. G. Lancaster, and M. J. Withford, “High slope efficiency and high refractive index change in direct-written Yb-doped waveguide lasers with depressed claddings,” Opt. Express 21(14), 17413–17420 (2013). [CrossRef] [PubMed]
48. C. Khurmi, N. B. Hébert, W. Q. Zhang, S. Afshar V, G. Chen, J. Genest, T. M. Monro, and D. G. Lancaster, “Ultrafast pulse generation in a mode-locked Erbium chip waveguide laser,” Opt. Express 24(24), 27177–27183 (2016). [CrossRef] [PubMed]
49. Z. Li, N. Dong, Y. Zhang, J. Wang, H. Yu, and F. Chen, “Mode-locked waveguide lasers modulated by rhenium diselenide as a new saturable absorber,” APL Photonics 3(8), 080802 (2018). [CrossRef]
50. S. Y. Choi, T. Calmano, F. Rotermund, and C. Kränkel, “2-GHz carbon nanotube mode-locked Yb:YAG channel waveguide laser,” Opt. Express 26(5), 5140–5145 (2018). [CrossRef] [PubMed]
51. T. L. Huang, H. C. Liang, K. W. Su, and Y. F. Chen, “Exploring the Emergence of the Self-Q-Switching in Diode-Pumped Yb:KGW Monolithic Lasers,” IEEE J. Sel. Top. Quantum Electron. 24(5), 1601106 (2018). [CrossRef]
52. P. H. Tuan, C. C. Chang, F. L. Chang, C. Y. Lee, C. L. Sung, C. Y. Cho, Y. F. Chen, and K. W. Su, “Modelling end-pumped passively Q-switched Nd-doped crystal lasers: manifestation by a Nd:YVO4/Cr4+:YAG system with a concave-convex resonator,” Opt. Express 25(3), 1710–1722 (2017). [CrossRef] [PubMed]
53. W. Li, J. Wu, X. Guan, Z. Zhou, H. Xu, Z. Luo, and Z. Cai, “Efficient continuous-wave and short-pulse Ho3+-doped fluorozirconate glass all-fiber lasers operating in the visible spectral range,” Nanoscale 10(11), 5272–5279 (2018). [CrossRef] [PubMed]
54. A. Härkönen, S. Suomalainen, A. Rantamäki, J. Nikkinen, Y. Wang, U. Griebner, G. Steinmeyer, and M. Guina, “1.34 μm VECSEL mode-locked with a GaSb-based SESAM,” Opt. Lett. 43(14), 3353–3356 (2018). [CrossRef] [PubMed]
55. N. Ming, S. Tao, W. Yang, Q. Chen, R. Sun, C. Wang, S. Wang, B. Man, and H. Zhang, “Mode-locked Er-doped fiber laser based on PbS/CdS core/shell quantum dots as saturable absorber,” Opt. Express 26(7), 9017–9026 (2018). [CrossRef] [PubMed]
56. A. Martinez, M. AI Araimi, A. Dmitriev, P. Lutsyk, S. Li, C. Mou, A. Rozhin, M. Sumetsky, and S. Turitsyn, “Low-loss saturable absorbers based on tapered fibers embedded in carbon nanotube/polymer composites,” APL Photonics 2(12), 126103 (2017).
57. X. Tian, H. Luo, R. Wei, C. Zhu, Q. Guo, D. Yang, F. Wang, J. Li, and J. Qiu, “Low-loss saturable absorbers based on tapered fibers embedded in carbon nanotube/polymer composites,” Adv. Mater. 30(31), 1801021 (2018). [CrossRef] [PubMed]
58. L. Lu, Z. Liang, L. Wu, Y. Chen, Y. Song, S. C. Dhanabalan, J. S. Ponraj, B. Dong, Y. Xiang, F. Xing, D. Fan, and H. Zhang, “Few-layer Bismuthene: Sonochemical Exfoliation, Nonlinear Optics and Applications for Ultrafast Photonics with Enhanced Stability,” Laser Photonics Rev. 12(1), 1700221 (2018). [CrossRef]
59. Q. Bao, H. Zhang, Y. Wang, Z. Ni, Y. Yan, Z. X. Shen, K. P. Loh, and D. Y. Tang, “Atomic-Layer Graphene as a Saturable Absorber for Ultrafast Pulsed Lasers,” Adv. Funct. Mater. 19(19), 3077–3083 (2009). [CrossRef]
60. W. J. Nie, Y. X. Zhang, H. H. Yu, R. Li, R. Y. He, N. N. Dong, J. Wang, R. Hübner, R. Böttger, S. Q. Zhou, H. Amekura, and F. Chen, “Plasmonic nanoparticles embedded in single crystals synthesized by gold ion implantation for enhanced optical nonlinearity and efficient Q-switched lasing,” Nanoscale 10(9), 4228–4236 (2018). [CrossRef] [PubMed]
61. G. Mie, “Articles on the optical characteristics of turbid tubes, especially colloidal metal solutions,” Ann. Phys. 25, 377–445 (1908). [CrossRef]
62. C. H. Kwak, Y. L. Lee, and S. G. Kim, “Analysis of asymmetric Z-scan measurement for large optical nonlinearities in an amorphous As2S3 thin film,” J. Opt. Soc. Am. B 16(4), 600–604 (1999). [CrossRef]
63. M. Bache and R. Schiek, “Review of measurements of Kerr nonlinearities in lithium niobate: the role of the delayed Raman response,” arXiv:1211.1721 (2012).
64. Y. H. Wang, X. X. Yu, F. Liu, and Y. M. Wang, “Nonlinear refraction of lithium niobate crystal doped with different metal nanoparticles,” Mater. Lett. 123, 35–37 (2014). [CrossRef]
65. A. López-Suárez, R. Rangel-Rojo, C. Torres-Torres, A. Benami, L. Tamayo-Rivera, J. A. Reyes-Esqueda, J. C. Cheang-Wong, L. Rodríguez-Fernández, A. Crespo-Sosa, and A. Oliver, “Enhancement of the optical Kerr effect exhibited by an integrated configuration of silicon quantum dots and silver nanoparticles,” J. Phys. Conf. Ser. 274(1), 012145 (2011). [CrossRef]
66. S. Zhang, N. Dong, N. McEvoy, M. O’Brien, S. Winters, N. C. Berner, C. Yim, Y. Li, X. Zhang, Z. Chen, L. Zhang, G. S. Duesberg, and J. Wang, “Direct observation of degenerate two-photon absorption and its saturation of WS2 and MoS2 monolayer and few-layer films,” ACS Nano 9(7), 7142–7150 (2015). [CrossRef] [PubMed]
67. N. Dong, Y. Li, Y. Feng, S. Zhang, X. Zhang, C. Chang, J. Fan, L. Zhang, and J. Wang, “Optical limiting and theoretical modelling of layered transition metal dichalcogenide nanosheets,” Sci. Rep. 5(1), 14646 (2015). [CrossRef] [PubMed]
68. M. Sheik-Bahae, A. A. Said, T. H. Wei, D. J. Hagan, and E. W. Van Stryland, “Sensitive measurement of optical nonlinearities using a single beam,” IEEE J. Quantum Electron. 26(4), 760–769 (1990). [CrossRef]
69. Z. Li, C. Cheng, N. Dong, C. Romero, Q. Lu, J. Wang, J. R. Vázquez de Aldana, Y. Tan, and F. Chen, “Q-switching of waveguide lasers based on graphene/WS2 van der Waals heterostructure,” Photon. Res. 5(5), 406–410 (2017). [CrossRef]
70. Y. Ren, G. Brown, R. Mary, G. Demetriou, D. Popa, F. Torrisi, A. C. Ferrari, F. Chen, and A. K. Kar, “7.8-GHz Graphene-Based 2-μm Monolithic Waveguide Laser,” IEEE J. Sel. Top. Quantum Electron. 21(1), 395–400 (2015). [CrossRef]
