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Abstract
Hybrid waveguides consisting of two-dimensional layered materials pad on the surface of optical waveguides suffer from a nonuniform and loose contact between the two-dimensional material and the waveguide, which can reduce the efficiency of the pulsed laser. Here, we present high-performance passively Q-switched pulsed lasers in three distinct structures of monolayer graphene-Nd:YAG hybrid waveguides irradiated by energetic ions. The ion irradiation enables the monolayer graphene a tight contact and strong coupling with the waveguide. As a result, Q-switched pulsed lasers with narrow pulse width and high repetition rate are obtained in three designed hybrid waveguides. The narrowest pulse width is 43.6 ns, provided by the ion-irradiated Y-branch hybrid waveguide. This study paves the way toward developing on-chip laser sources based on hybrid waveguides by using ion irradiation.
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1. Introduction
Due to miniaturization, enhanced optical gain, and low pump threshold, passively Q-switched pulsed laser based on optical waveguides is one of the most promising compact and robust laser sources for future on-chip integrated devices, which has a broad range of applications ranging from materials processing to nonlinear optics and sensing [1–3]. Waveguides with diverse configurations such as planar or channel, photonic-lattice-like or Y-branch, and standard or cladding have been employed as a necessary laser gain medium for the generation of pulsed lasers [4–9]. Among those configurations, a cladding structure constructs a gradient refractive index increasing from the outer layer to the guiding core, providing higher optical confinement and coupling efficiency in the core. For example, the surface cladding waveguides prepared by ion irradiation show higher intensity density and enhanced laser performances in comparison to the corresponding monolayer waveguides [10]. Benefiting from the tiny guiding core of cladding structures, superior Q-switched pulsed waveguide lasers have been achieved in various cladding-like waveguides [11–13].
Since its first discovery, graphene has attracted strong interest in photonics [14,15]. Due to the ultrathin layered structure, ultra-wide working bandwidth as well as ultrafast recovery time, graphene is regarded as a promising chip-scale broadband saturable absorber (SA) in ultrafast laser generation, which plays a major role in system miniaturization [16,17]. In the past few years, graphene has been widely applied to realize passively Q-switched and mode-locked waveguide lasers based on diverse waveguide structures. For instance, pulsed waveguide lasers can be generated using a direct-field-interaction configuration of the graphene attached to the end face of a buried waveguide [18–20]. Such a cavity involves full optical power when the graphene interacts with waveguide light, leading to a low laser damage threshold of the SA. For surface waveguides, a hybrid waveguide can be formed by coating graphene on the top of waveguides, where the graphene interacts with light via an evanescent field [17,21–23]. Owing to the low intensity of the evanescent wave, this configuration not only increases the damage threshold of graphene but also provides a compact integrated cavity. However, the weak optical absorption of monolayer graphene (2.3%) leads to insufficient interaction with evanescent waves when using a short waveguide cavity. In addition, the evanescent field is sensitive to distance. Monolayer graphene used in this scheme suffers from loose contact with the waveguide because of intrinsic wrinkles and ripples, further hampering the coupling of the graphene with the evanescent field of the waveguide modes [24]. Although the monolayer graphene is ideal for reducing the volume of lasers, the limited interaction length with the evanescent wave leads to difficulties in saturating monolayer graphene or the long interval required for saturation, hindering the realization of short pulses. To date, passively Q-switched waveguide lasers based on monolayer graphene interacting with laser modes via the evaporative field are rarely reported. Q-switched pulses with a pulse width of 124 ns have been achieved only in a Yb:Y2O3 planar waveguide [25]. It has not been investigated in channel hybrid waveguides, which can present an enhanced evanescent field. Therefore, in order to improve the performance of Q-switched pulsed lasers (e.g., short duration, high peak power) of the hybrid waveguides while pursuing device compactness, urgent demands have emerged for finding ways to increase the interaction strength of monolayer graphene with guided light in the evanescent-field-interaction configuration.
The energetic ion has been proven to be an effective technology to modify the properties of two-dimensional layered materials and optimize the performance of related devices due to an abundant supply of irradiation conditions, including ion species, energy, and fluence. For example, the ion beam can induce defects in layered nanomaterials to tailor their electronic structures and optical properties [26–28]. More importantly, some research works have illustrated that high-energy ion beams could enhance contact between graphene nanosheets and substrates, resulting in significantly improved device performances [29,30]. These studies make ion irradiation promising for modulating the distance and coupling between monolayer graphene and the optical waveguide. To the best of our knowledge, the use of ion irradiation techniques to enhance the contact of monolayer graphene with optical waveguides and improve the performance of waveguide lasers has not been explored.
In this work, we design three types graphene-Nd:YAG hybrid waveguides irradiated by high-energy carbon ion beams. The passively Q-switched pulse laser performances of hybrid waveguides before and after ion irradiation are systematically studied and compared. In comparison with the hybrid waveguide laser systems without ion irradiation, the ion-irradiated systems have a shorter duration, higher pulse energy, and enhanced slope efficiency. This work demonstrates that ion irradiation is an effective tool for resolving the issue of the interaction strength of monolayer graphene with the evanescent wave, providing an attractive means to realize high-performance micro- and nano-photonic devices.
2. Sample preparation
The Nd:YAG crystal (doped by 1 at.% Nd3+ ions) is cut into dimensions of 10 × 10 × 2 mm3 with one 10 × 10 mm2 facet and two 10 × 2 mm2 facets optically polished. Figure 1(a) displays the preparation steps of three hybrid waveguides. Firstly, the biggest polished surface (10 × 10 mm2) of crystals is successively irradiated by carbon (C3+) ions at energy (fluence) of 6.5 MeV (1 × 1015 ion/cm2) and 17 MeV (2 × 1014 ion/cm2), which is performed at the Ion Beam Centre of Helmholtz-Zentrum Dresden-Rossendorf, Germany. The carbon beam direction is tilted by 7° off the normal axis of the crystal surface to avoid the channeling effect. As a result, a planar cladding waveguide with a thickness of nearly 10 µm can be formed on the crystal near-surface region. Secondly, a Ti:Sapphire regenerative amplifier (Spitfire, Spectra Physics, USA), which delivers 795 nm pulses with a duration of 120 fs and a repetition rate of 1 kHz, is employed to fabricate channel cladding waveguides on the planar waveguide layer, as can be seen from step 2. During the laser-writing process, the incident laser beam with a pulse energy of 0.6 µJ is focused through the largest crystal surface (10 × 10 mm2) by a 40 × microscope objective (NA = 0.65). The crystal is scanned at a constant velocity of 0.5 mm/s in the direction paralleled to the 10-mm edge, producing a laser-damage track along the crystal. A few parallel scans are performed, with a lateral separation of 3 µm, at different depths beneath the crystal surface to obtain the desired channel waveguides. To investigate how the waveguide structure influences the performance of the pulsed laser, we design three different channel waveguides in Nd:YAG crystal: a half-ring straight waveguide, a rectangular straight waveguide, and a rectangular Y-branch waveguide. Furthermore, another intention of choosing those structures is to verify the effectiveness and wide applicability of ion irradiation for optimizing hybrid waveguide lasers with different geometries (i.e., half-ring and rectangular) borrowed from the structures commonly used to generate pulsed waveguide lasers based on evanescent-field interaction [7,12]. Finally, a monolayer graphene (produced by the chemical vapor deposition and supplied by 6Carbon Technology, China) with a size of slightly less than 10 × 10 mm2 is transferred on the surface of channel waveguides to constitute hybrid waveguides and subsequently irradiated by C3+ ions at an energy of 7.5 MeV and a fluence of 1 × 1015 ions/cm2 at Peking University. The irradiated graphene-Nd:YAG hybrid waveguides are named W1 for the half-ring straight waveguide, W2 for the rectangular straight waveguide, and W3 for the rectangular Y-branch waveguide, respectively. For comparison under the same waveguide preparation conditions, the irradiated graphene is cleaned off waveguides after the laser experiment. Then, new monolayer graphene with the same size is transferred on the waveguide again to form reference hybrid waveguides, i.e., the hybrid waveguides without ion irradiation, named W10, W20, and W30, respectively.
Fig. 1. (a) Schematic diagram of the fabrication process of hybrid waveguides under ion irradiation. Step 1: ion irradiation for a planar cladding waveguide. Step 2: ultrafast laser writing for channel cladding waveguides. Step 3: monolayer graphene coated on the surface of waveguides and irradiated by carbon ions. (b) Optical microscope images of channel cladding waveguides.
Figure 1(b) presents the microscopic images of the cross sections and the top view of each surface channel cladding waveguide (referred to W10-W30). As one can see from the input facet and output facet images, W10 has a half-ring cross-section with a diameter of 50 µm. W20 has a rectangular cross profile of 30 × 30 µm2. In particular, W30 is made up of a rectangular straight waveguide (30 × 30 µm2) divided into two divergent identical waveguides (30 × 30 µm2). The length of the straight waveguide and splitting waveguide is 3.5 mm and 6.5 mm, respectively. The distance between the two exits of the Y-branch is 190 µm. It needs to be emphasized that the cross sections of the three waveguides have cladding-like distributions. The outer cladding is laser-damage tracks. The inner cladding is located between the irradiated and ultrafast laser writing regions. And the core is the region irradiated by carbon ions, which exhibits a larger color change, implying a rise in refractive index. The propagation losses of the channel waveguides are studied at 1064 nm using an end-face coupling system as well as determined by direct measurement of the laser powers from the input and output end-faces. The half-ring straight waveguide, rectangular straight waveguide, and rectangular Y-branch waveguide show a propagation loss of around 1.51, 1.69, and 2.78 dB along the TE polarization while around 1.58, 1.67, and 2.88 dB along the TM polarization, respectively.
The monolayer graphene film placed on the surface of the Y-branch waveguide is optically imaged in Fig. 2(a), demonstrating the high homogeneity of the as-transferred sample. The evidence for the high-quality monolayer graphene can be found in the Raman spectrum excited by a 514 nm laser in Fig. 2(b). The intensity ratio of 2D peak to G peak is 2.1 (I2D/IG), implying the nature of monolayer graphene [31]. In addition, the D peak (1353 cm-1) associated with defects and disorder has negligible intensity, which indicates the highly crystalline of the as-prepared monolayer graphene.
Fig. 2. (a) Optical imaging of monolayer graphene film on the surface of Nd:YAG waveguides. (b) Raman spectrum of monolayer graphene measured at the rectangular region in (a).
3. Passively Q-switched waveguide laser
To investigate the pulsed laser performance of the fabricated hybrid waveguides, we carry out an end-face coupling experiment with the setup schematically shown in Fig. 3(a). A linearly polarized laser from a tunable CW Ti:sapphire laser (Coherent MBR-110) is employed as a pump light with a wavelength centered at 808 nm. To couple the pump laser into the channel waveguides efficiently, two plano-convex lenses with focal lengths of 50 mm and 25 mm are used. They produce approximately 50- and 25-µm focal spot sizes at 808 nm, respectively. The 25-µm focal spot size is better matched to the thickness of the channel waveguides (∼ 30 µm). Thus, the 25-mm plano-convex lens is ultimately used as the incoupling lens. To form a compact Fabry-Pérot cavity, an input mirror (with a transmission of 99% at ∼808 nm and a reflectivity >99.9% at ∼1064 nm) and an output mirror (with a transmission of 85% at ∼1064 nm and a reflectivity >99% at ∼808 nm) are adhered to the input and output end facets of the waveguide, respectively. Here, channel waveguides serve as gain media. Monolayer graphene before and after ion irradiation is used as SA and coupled with the waveguide mode by the evanescent field. The generated pulse lasers are collected by a 20 × microscope objective lens (NA = 0.4) and detected by a spectrometer, an infrared CCD, a power meter, and an oscilloscope, respectively.
Fig. 3. (a) Schematic diagram of the experimental setup for passively Q-switched waveguide laser. (b) Emission spectrum of passively Q-switched waveguide laser.
The passively Q-switched pulse lasers along TE and TM polarization are obtained in all waveguide configurations (W1-W3 and W10-W30) with an oscillation wavelength of 1062 nm, as shown in Fig. 3(b). Notably, due to ion irradiation further enhancing the optical confinement of the Nd:YAG waveguide along the TE polarization direction, the lasing performance of ion-irradiated hybrid waveguides along TE polarization is superior to that of the laser along TM polarization. Our results for the lasers below are measured along the TE polarization. The intensity of the laser modes detected by the infrared CCD are normalized for each measurement.
3.1 Passively Q-switched laser operated in the half-ring straight waveguide
The passively Q-switched laser performance based on the half-ring straight waveguide (W1 and W10) has been demonstrated in Fig. 4. Figure 4(a) presents the output power as a function of pump power. According to the linear fitting curves, the lasing thresholds of the pulsed laser generated by W1 and W10 are calculated to be 152 mW and 98 mW, respectively. Meanwhile, the output power reaches the maximum at 138 mW (W1) and 104 mW (W10) at the pump power of 455 mW and 472 mW, corresponding to the slope efficiency of 43% and 28%, respectively. Figure 4(b) shows the single pulse train under the maximum pump power, in which the minimum pulse duration is 47.6 ns (67.1 ns) for W1 (W10). Furthermore, the measured laser modes of both laser systems exhibit a multi-mode profile, as shown in the inset of Fig. 4(b). Figures 4(c), 4(d), 4(e), and 4(f) depict the dependence of pulse duration, repetition rate, pulse energy, and peak power as a function of pump power. As the increase of the pump power, the duration of W1 (W10) rapidly decreases from 390 ns (206 ns) to 47.6 ns (67.1 ns). The variation of the repetition rate of W10 follows the same tendency as that of W1, with a maximum repetition rate of 3.1 MHz. Moreover, the maximum single pulse energy of the two pulsed lasers reaches 44.5 nJ (W1) and 33.6 nJ (W10), corresponding to a maximum peak power of 935 mW and 679 mW, respectively. Based on these results, it can be concluded that the passively Q-switched waveguide laser based on W1 has much higher slope efficiency, shorter duration, higher pulse energy, and higher peak power compared to W10, which demonstrates the enhanced laser performance of monolayer graphene-Nd:YAG hybrid waveguide irradiated by the ion beam.
Fig. 4. Passively Q-switched laser generated from W1 and W10. (a) Output power versus pump power. (b) Recorded single train of the pulse laser. Inset is the laser mode. (c) Pulse duration versus pump power. (d) Repetition rate versus pump power. (e) Pulse energy versus pump power. (f) Peak power versus pump power.
3.2 Passively Q-switched laser operated in the rectangular straight waveguide
Figure 5 describes the output characteristics of passively Q-switched lasers generated in rectangular straight waveguides (W2 and W20).
Fig. 5. Passively Q-switched laser generated from W2 and W20. (a) Output power versus pump power. (b) Recorded single train of the pulse laser. Inset is the laser mode. (c) Pulse duration versus pump power. (d) Repetition rate versus pump power. (e) Pulse energy versus pump power. (f) Peak power versus pump power.
As shown in Fig. 5(a), when the pump power exceeds 109 mW and 146 mW, steady pulsed lasers are achieved in W2 and W20, respectively. Pulsed lasers based on W2 exhibit relatively higher output power (93 mW) and slope efficiency (27%) compared to W20. The single pulse train in Fig. 5(b) shows that the minimum pulse duration of the two lasers remains essentially the same. The inset of Fig. 5(b) displays the laser mode profiles, in which a multi-mode distribution is shown. Figure 5(c) shows the variation of the pulse duration for the rectangular straight waveguide, similar to the half-ring straight waveguide system, where the duration first decreases rapidly with increasing pump power and then stabilizes at approximately 50 ns. In addition, Fig. 5(d)–5(f) depict the repetition rate, pulse energy, and peak power versus pump power, respectively, in which the maximum repetition rate produced in W2 is 3.0 MHz, corresponding to a pulse energy of 30.8 nJ and a peak power of 581 mW. For W20, the value is 2.7 MHz, 16.5 nJ, and 305 mW, respectively. From the above results, it is obvious to see that the laser performance of W2 is better than that of W20, confirming the effectiveness of ion irradiation for optimizing hybrid waveguide lasers.
3.3 Passively Q-switched laser operated in a rectangular Y-branch waveguide
At last, passively Q-switched lasers based on a Y-branch hybrid waveguide (W3 and W30) are realized.
As can be seen from Fig. 6(a), the pump threshold, the output power, and the slope efficiency of Y-branch waveguide lasers have been greatly improved after ion irradiation. For W3, as the pump power increases to 128 mW, the Q-switched pulse starts to appear. At the same time, the output power increases approximately linearly with the increase of pump power, resulting in a slope efficiency of 20%. According to the single pulse sequence in Fig. 6(b), it can be seen that the pulse width of the irradiated system is remarkably narrower than that of the non-irradiated hybrid waveguide laser. The inset of Fig. 6(b) displays the measured mode profiles of both lasers under the same pumping conditions, showing the multi-mode distribution. It is noteworthy that the guided modes of the pulse laser based on the Y-branch waveguide are excited not only in the branches but also in the planar region between the branches. This phenomenon has not been observed in other Y-branch waveguide pulse lasers, whether the SA interacts with the waveguide mode via an evanescent field or direct field [7,32]. Moreover, as illustrated in Fig. 6(c), the pulse duration of the waveguide laser based on W3 and W30 decreases with increasing pump power. The W3 laser system exhibits a significantly shorter pulse width with a minimum of 43.6 ns. It can be concluded from Fig. 6(d), 6(e), and 6(f) that the pulsed laser based on the irradiated SA has a larger repetition frequency, pulse energy, and peak power, with the maximum values of 3.1 MHz, 24.1 nJ, and 553 mW, respectively. Therefore, in contrast to W30, the Q-switched waveguide laser in W3 has superior performance. This further confirms the ability of the ion beam technology to modulate the laser performance of hybrid waveguides.
Fig. 6. Passively Q-switched laser generated from W3 and W30. (a) Output power versus pump power. (b) Recorded single train of the pulse laser. Inset is the laser mode. (c) Pulse duration versus pump power. (d) Repetition rate versus pump power. (e) Pulse energy versus pump power. (f) Peak power versus pump power.
4. Discussion
Based on the passively Q-switched waveguide laser results, it can be found that:
- (A) High-energy ion irradiation can improve the lasing performance of the three hybrid waveguides to different degrees. The optical properties of the Q-switched pulses of the hybrid waveguide are determined by the interaction strength between the guiding mode and the monolayer graphene. While the evanescent field of the guiding mode shows exponential decay on the waveguide surface. The closer the SA is to the waveguide surface, the more laser is absorbed. Before ion irradiation, the monolayer graphene and the waveguide are separated by a significant distance due to the presence of a large number of wrinkles and folds in graphene, resulting in a poor interaction between the graphene and the guided light through an evanescent field, as illustrated in Fig. 7(a). As a result, this laser system provides a low laser output power as well as a broad pulse width. In contrast, when the hybrid waveguide is irradiated with high-energy carbon ions, the high-energy ions transfer energy to graphene, resulting in numerous near-surface atoms in graphene being excited and gaining momentum in the direction of the incident ions [30,33]. Hence, graphene is flattened and tightly squeezed on the waveguide surface, as shown in Fig. 7(b). We believe that the compressed monolayer graphene interacts strongly with the evanescent field, which greatly enhances the optical performance of the Q-switched pulsed lasers in the hybrid waveguide.
- (B) Compared to the straight waveguides, the Y-branch hybrid waveguide exhibits the greatest improvement in lasing performance in terms of typical parameters, such as output power (the maximum values are lifted 4.5 times), pulse duration as well as pulse energy. The mode profile of W3 described in Section 3.3 exhibits a strong mixed mode in the planar region between the branches, implying that the laser in the planar waveguide is also more coupled into the SA, as illustrated by the schematic diagram in Fig. 7(c). Therefore, when the irradiated Y-branch hybrid waveguide is pumped, pulsed laser oscillations are present not only in both branches but also in the planar portion between the branches. However, the surface size of the straight waveguides is always the same before and after the ion irradiation. Consequently, pulsed waveguide lasers based on Y-branching structures are more sensitive to ion irradiation than lasers based on two types of straight waveguides.
- (C) The pump threshold decreases for the two rectangular waveguides after ion irradiation, while the pump threshold for the half-ring waveguide increases to 152 mW. The reason for the increasing threshold we attribute to the loss caused by the larger cross-section size of the half-ring waveguide. The large cross-sectional size of this waveguide makes it less affected by the absorption loss induced by graphene after ion irradiation. In contrast, for rectangular straight and Y-branch waveguides with relatively small dimensions, graphene absorption plays a dominant role in the losses. Nevertheless, the half-ring waveguide with larger radii shows excellent laser performance in terms of the maximum output power (138 mW) and slope efficiency (43%), according to the comparison of the pump-output dependences of irradiated three hybrid waveguide lasers in Fig. 7(d). Those values are higher than 93 mW and 27% for W2 as well as 75 mW and 20% for W3. In addition, at a pump power of 455 mW, the minimum pulse duration of 47.6 ns for W1 is slightly smaller than that of W2 (53.0 ns) and slightly wider than that of W3 (46.1 ns), as displayed in Fig. 7(e). The minimum pulse width obtained from W3 is caused by the additional optical absorption provided by its planar region since the pulse duration is inversely proportional to the modulation depth (absorption loss) of the SA. These results show that by adjusting the cross-sectional dimensions of the surface Y-branch waveguide and the distance between the two branches, it is possible to make the waveguide capable of supporting a large peak power of the laser and significantly narrow pulse width.
Fig. 7. (a), (b) Schematic illustration showing the coupling of graphene and evanescent wave before and after carbon ion irradiation. (c) Schematic top view of passively Q-switched laser generated by W1-W3. (d) Output power as a function of pump power obtained from W1-W3. (e) Pulse trains of W1-W3.
To date, several works related to monolayer graphene SA in different waveguide laser configurations have been reported, which are summarized in Table 1. Regarding Q-switch lasers based on the direct-field interaction of graphene with waveguide laser, a Y-branch waveguide was employed in Yb:YAG crystal to generate 42 ns/178 nJ (duration/energy) pulses [32]. A relatively wider pulse width and lower pulse energy were acquired using a circular straight Nd:YVO4 waveguide, yet a higher repetition rate of 8.897 MHz was produced [34]. However, it is noteworthy that the greatest performance of both these lasers was realized at a high pump power. As for the laser tuned by monolayer graphene via an evanescent field, a Q-switched pulse with maximum pulse energy of 83 nJ, corresponding to a pulse width of 124 ns and a repetition rate of 1.64 MHz, was confirmed in a Yb:Y2O3 planar waveguide at a pump power of 1052 mW [25]. In contrast, utilizing irradiated graphene-Nd:YAG hybrid waveguides, we have achieved both a relatively short duration and a high repetition rate. Moreover, the maximum pulse energy of 44.5 nJ (based on the half-ring straight waveguide) is obtained at a lower pump power (less than 500 mW). Combining a pulse duration of 43.6 ns and a repetition rate of 3.1 MHz, our Q-switched Y-branch waveguide laser outperforms the previously reported Y-branch waveguide laser using 6-8 layers of graphene absorbing laser via an evanescent-field interaction [7]. Notably, the output power in our work is not saturated at high pump power. Therefore, the results of the Q-switched lasers mentioned in Section 3 are limited by the pump power of the pump source. Higher pulse energies (E = Poutput/RR) and higher peak powers (PPeak = E/FWHM) can be delivered if the pump power is increased further, where Poutput and PPeak are the output power and peak power, respectively.
Table 1. Comparisons of Q-switched pulsed waveguide laser by direct and evanescent-field interaction with monolayer graphenea
To the best of our knowledge, we enhance the coupling between monolayer graphene and evanescent waves for the first time in a hybrid waveguide utilizing ion irradiation. The optimized Q-switched pulsed lasers are provided in three ion-irradiated hybrid waveguides, demonstrating the potential of ion beams to enhance on-chip integrated lasers. From the discussion above, we can determine that W1 has the best laser performance, although its minimum pulse duration is not the shortest. Moreover, W3 has the smallest pulse width, but the other laser parameters are not as good as the corresponding straight waveguide laser systems. All waveguides show multimode lasers. The values of the maximum repetition rate of the three irradiated laser systems are quite comparable (about 3.1 MHz). Benefiting from the involvement of partial intracavity optical power, pulsed waveguide lasers under an evanescent-field-interaction scheme offer miniaturized laser sources while indirectly raising the laser damage threshold of the SA. The combination of flexible optical waveguide structures, a wide variety of 2D materials, and ion beam conditions is expected to further present Q-switched lasers with higher peak power and mode-locked lasers in the spectral range from visible to mid-infrared, providing diverse laser sources for on-chip integrated systems.
5. Conclusion
In conclusion, we have experimentally designed three hybrid waveguide structures irradiated by heavy ion beams and achieved optimized passively Q-switched pulse lasers. The hybrid waveguide laser system applies Nd:YAG channel waveguide as a gain medium and monolayer graphene as a SA, operating at 1-micron wavelength, in the megahertz-range repetition rates. The pulse lasers based on irradiated hybrid waveguide exhibit greater slope efficiency (twice as high as that of the unirradiated system), shorter duration, and peak power. The best slope efficiency of 42% and the maximum pulse energy of 44.5 nJ are generated from the irradiated half-ring waveguide cavity. While the minimum pulse duration of 43.6 ns is obtained in the irradiated Y-branch waveguide. The obtained results suggest that it is hopeful to realize a mode-locked waveguide laser by designing the ion beam irradiated hybrid waveguide under reasonable ion beam conditions. This work provides a feasible solution for optimizing near-infrared integrated pulsed light sources.
Funding
National Natural Science Foundation of China (12205167).
Acknowledgments
The authors acknowledge Prof. F. Chen and Mr. Q. Lu from Shandong University for their kind help with crystal processing and lasing performance characterization.
Disclosures
The authors declare that there are no conflicts of interest related to this article.
Data availability
Data will be made available on request.
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