Open Access
Add to BibSonomy
Abstract
A high-efficiency Raman conversion from 1.987 µm to 2.177 µm is demonstrated experimentally in 45 m GeO2-doped silica fiber, adopting a dissipative soliton resonance (DSR) rectangular pulse as the pump. Over the entire spectral distribution, the spectral purity of the first-order Raman pulse is up to 96.8%, suggesting a nearly complete pump depletion before the onset of cascaded Raman shifts. The corresponding pump-to-Raman conversion efficiency of 67.4% is the highest up to date in this spectral region. Meanwhile, a large Raman pulse energy of 1.03 µJ was obtained at the repetition rate near MHz level, corresponding to 0.893 W average power. In the total output, the Raman-dominated spike has a Full Width Half Maximum (FWHM) of 1.18 ns far narrower than DSR’s pulse duration of 10.25 ns. The results indicate that DSR is a promising candidate for developing efficient Raman nanosecond pulse fiber laser in mid-infrared (MIR) region.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
Driven by the needs of laser wavelength diversity in numerous applications (e.g. polymer processing [1], gas detection [2], military countermeasures [3], biomedical sector [4], etc), the rapid development of MIR short pulse fiber lasers has been made. Therein, rare-earth-doped (Tm3+, Ho3+, Er3+, Dy3+) fiber lasers played a crucial role in the wavelength extension of MIR short pulses. Combining with various pulse modulation techniques, their operating wavelengths have been successfully expanded to ∼2.1 µm [5,6] and 2.7∼3.7 µm [7,8]. However, due to the emission bandwidth limitation of rare-earth-doped fibers, these lasers cannot provide the short pulses in 2.1∼2.7 µm waveband to satisfy some special demands for above applications. Fortunately, Raman fiber laser (RFL) (first reported by R. H. Stolen in 1972 [9]), a nonlinear laser based on the stimulated Raman scattering (SRS) phenomenon inside the fiber, provides a feasible way to attack the mentioned issue. In virtue of a befitting pump and fiber combination, it enables the laser wavelengths to be shifted towards our desired position within the fiber’s transmission window. Along with the researches on physical mechanism, fiber materials and key techniques going deep, RFLs have advanced greatly in power raising [10,11], spectral quality improvement [12], wavelength extension [13,14] and so on. In MIR spectral region, a 3.7 W continuous wave (CW) fluoride glass RFL at 2.23 µm [11] and a quasi-CW chalcogenide glass RFL with the longest wavelength of 3.77 µm [13] have been reported respectively. Gauthier et al. demonstrated a tunable ultrafast pulse source reaching up to 4.8 µm [14], relying on a special SRS regime (soliton self-frequency shift) in InF3 fiber. These highlighted the great potential of the RFLs for developing the laser wavelength diversity.
To date, a few efforts have been deployed to investigate MIR nanosecond short pulse RFLs at >2.1 µm, through the SRS effect in soft glass fibers and GeO2-doped silica fibers. Most recently, based on nanosecond pulse pumping, the maximum cascaded Raman shifts at 3.425 µm and at 2.438 µm have been implemented in As2S5 fiber [15] and in fluorotellurite fiber [16] respectively. Nevertheless, their mechanical robustness and power scaling is still a quite tough nut. In contrast, GeO2-doped silica fiber is significantly more favored, attributing to low transmission loss, strong resistance to damage, ease of all-fiber integration, etc. Using GeO2-doped fiber, the first demonstration on all-fiber MIR Raman pulse laser was reported in 2008 [17]. Pumped by 1.53 µm gain-modulated nanosecond pulses, Rakich et al. achieved the pump-to-Raman conversion of 37% at 2.15 µm and 16% at 2.43 µm. Subsequently, aiming at the power scaling and the wavelength extension, Jiang et al. realized the second-order Raman shifts from 2.008 µm to 2.43 µm and from 2.04 µm to 2.48 µm with the help of a 100 ns Q-switched pulse pumping [18]. Due to the Raman gain saturation and emission noise caused by the generation of the cascaded Raman shifts, the efficiencies (average powers) of the first-order Raman pulses were just 19.2% (0.35W) at 2.2 µm and 20.3% (0.38 W) at 2.24 µm. By adjusting fiber length to restrain the cascaded Raman shifts, the average power of Raman pulse at 2.2 µm was scaled up to the watt level, corresponding to the Raman conversion efficiency of 35.9% [19]. Whereas, the Raman gain reduction caused a large pump remnant (>1 W) in the total output. Moreover, the Raman shift from 2.2 µm to 2.43 µm was not prevented entirely. Recently, Du et al. illustrated a novel 2166 nm Raman pulse resonator where the pulse duration can be tuned from 0.9 ns to 4.4 ns, using 22 m Ge-core fiber pumped by 1981nm noise-like pulse and the cavity matching scheme [20]. In this system, the unwanted component was suppressed well. It was a pity that the pulse average power (energy) was only 52.65 mW (12.15 nJ). From the results above, it was evident that previous works one-sidedly focused on MIR Raman pulse generation or power raising based on nanosecond Gaussian pulse pumping. But the impacts of pump pulse shape on the Raman conversion efficiency at desired wavelengths was neglected.
Actually, some early studies on the wavelength conversion in visible or near-infrared region have verified that rectangular pulse was superior to promote pump energy transfer [21–24], comparing to Gaussian pump pulse. Since it offered the nearly consistent Raman gain across the temporal profile. Traditional rectangular short pulses were mainly generated by diode-seeded pulse-shaping techniques [25,26]. However, limited by the existing fabrication and high cost, they have been hardly applied in MIR spectral region. Recently, a novel wave-breaking-free rectangular pulse called DSR with MHz-level repetition rate appeared in all-fiber 1-, 1.5- and 2-µm mode-locking oscillators [27–29]. In contrast to other mode-locked pulses (e.g. conventional soliton, stretched pulse, noise-like pulse, etc.), DSR has adjustable pulse duration at a constant peak power, high pulse energy comparable to the Q-switched or gain-modulated pulses, etc. More significantly, DSR dispensed with the use of pulse-shaping system in the pulse generator and amplifier [25,29]. These outstanding features motivated us to explore DSR’s potential in efficient MIR Raman pulse generation which has never been investigated.
Herein, we experimentally report a 2.177 µm efficient all-fiber-integrated Raman pulse laser consisting of a 1.987 µm DSR-based Tm-doped fiber laser pumping and 45 m Ge-core Raman silica fiber. DSR’s output characteristics both in the Tm-doped fiber oscillator and amplifier were investigated in detail. By appropriately adjusting DSR’s pulse duration and peak power, the maximum pump-to-Raman conversion efficiency of 67.4% was achieved with the Raman output power of 0.893 W. In the total output, the laser spectrum exhibited a Raman spectral purity of up to 96.8% and the Raman-dominated spike had a FWHM of 1.18 ns. In this case, the Raman pulse energy was calculated to be 1.03 µJ, corresponding to the repetition rate of 865.1 kHz.
2. Experimental setup
As shown in Fig. 1, Raman pulse fiber laser is mainly composed of a DSR-based Tm-doped fiber laser system as the pump and a piece of Raman fiber. In the Tm-doped fiber laser system, a typical nonlinear polarization evolution (NPR) mode-locking Tm-doped fiber oscillator seed was built to generate the DSR pulse. A 793 nm laser diode with 12 W maximum output power was used to pump 3 m Tm-doped fiber (CorActive, DCF-TM-10/128) through a fiber pump combiner. The total pump absorption of up to 92% provided the laser gain enough for realizing the generation of DSR pulse. To excite the peak power clamping effect (PPCE) required for the DSR formation, ∼230 m SMF28e fiber was adopted to enhance the nonlinear effect in the cavity. The polarization independent isolator (PI-ISO) was employed to guarantee unidirectional laser operation. 45° tilted fiber grating (TFG) was combined with the polarization controllers (PCs) on its both sides, acting as an artificial saturable absorber to induce NPR effect. By controlling the PCs to finely adjust intracavity polarization, the DSR mode-locking performance could be further optimized. In the oscillator with 239 m cavity length, cavity net dispersion was around -19.13 ps2 at 1.98 µm. This indicated that DSR was generated at a large anomalous dispersion regime. 7/3 fiber output coupler provided 30% DSR signal for the follow-up work. In order to monitor DSR state in real time, the laser output was divided into 2 parts with the help of a 1/9 fiber coupler. Therein, 90% portion was served as the seed signal of the one-stage Tm-doped fiber amplifier. In the amplifier, the PI-ISO and the pump-to-gain structure used here were similar to the oscillator but a longer Tm-doped fiber (4.5 m) was used to enhance the laser gain. Another PC was adopted to optimize the polarization direction of the seed signal. The most crucial Raman gain fiber is 45 m highly GeO2-doped silica fiber (Nufern) with 2.4 µm fiber core diameter. For the laser output, the spectral profile was measured by a spectrum analyzer (Yokogawa AQ6375) with 0.05 nm high resolution and 1.2∼2.4 µm wide spectrum range. An InGaAs photodetector (EOT ET-5000F) with a fast response time of 28 ps was used to detect temporal signal and the radio frequency (RF) spectrum, by connecting with a 6 GHz digital oscilloscope (R&S RTO) and an RF spectrum analyzer (YIAI AV4033A) respectively.
Fig. 1. Experimental setup of efficient all-fiber Raman pulse laser based on the DSR pumping. LD: laser diode, DC-TDF: double cladding Tm-doped fiber, OC: optical coupler, PI-ISO: polarization-insensitive isolator, 45° TFG: 45° tilted fiber grating, PC: polarization controller.
3. Experimental results and discussion
3.1 DSR pulse generation and amplification
In the oscillator, CW operation was observed when the pump power reached 0.59 W. Such high laser threshold was mainly due to the large intracavity loss originating from high laser output ratio and long cavity length. By adjusting the PCs’ position carefully, the DSR mode-locking operation was achieved at the pump power of 1.46 W. In the cavity, the theoretical time required for the DSR formation is usually at µs∼ms scale [30,31]. The evolutions of DSR’s temporal and spectral profile with respect to the pump power were demonstrated in Figs. 2(a) and 2(b) respectively. In Fig. 2(a), the DSR’s amplitude kept unchanged but the pulse duration could be tuned linearly from 2.34 ns to 14.08 ns as the pump power enhancement. The fitting slope with respect to the pump power is 3.34 ns/W, characterizing the performance of pulse duration tuning. The spectra in Fig. 2(b) illustrate that DSR has a center wavelength of 1986.6 nm. The spectral 3-dB bandwidth varied from 10.8 nm to 14.3 nm by reason of slightly spectral broadening (∼3.5 nm) induced by self-phase modulation (SPM) effect. Figure 2(c) shows that the pulse peak power is clamped at ∼5.4 W. At the maximum pump power, the pulse energy reached 78.43 nJ with the output average power of 67.85 mW and the pulse duration of 14.08 ns. At this state, a signal-to-noise ratio of up to 61.5 dB and the fundamental repetition rate of 865.1 kHz were obtained from Fig. 2(d). In the inset, the measured pulse separation (1.16 µs) was coincident with the theoretically intracavity round-trip time, indicating that the oscillator operated at a fundamental continuous-wave mode-locking (CWML) state.
Fig. 2. DSR’s output characteristics. (a) The evolution of DSR’s temporal profile versus 793 nm pump power. (b) Output spectra corresponding to (a). (c) Pulse duration, average power, pulse energy and peak power as functions of the pump power. (d) At the maximum pump power, narrow RF spectrum at the fundamental repetition rate (RBW: 40 Hz), inset: wideband RF spectrum in 500 MHz spanning range (RBW: 3 kHz) (top) and the corresponding pulse train (bottom).
Figure 3(a) illustrates the output average power of the amplified DSR at different pulse durations when the launched 793 nm pump power increases from 2.21 W to 6.15 W. At the pump power of 6.15 W, the maximum output power ranging from 0.95 W to 1.83 W could be obtained with the pulse duration increment in which the seed power fed into the amplifier was varied from 9 mW to 61 mW. Accordingly, the slope efficiency also experienced a notable change from 18.9% to 35.8%. At the pump power of 6.15 W, the amplified pulse energy and peak power as a function of the pulse duration is presented in Fig. 3(b). The maximum pulse energy of 1.1 µJ∼2.11 µJ and the corresponding peak power of 470 W∼150 W were obtained, when DSR’s pulse duration was broadened from 2.34 ns to 14.08 ns. In the inset of Fig. 3(b), the waveforms of the DSR at the pulse duration of 10.25 ns were compared before and after the amplification. It was evident that no pulse distortion or broadening occurred in the amplifier since these peak power levels were not high enough to trigger any detrimental nonlinear effects. This is extremely in favor of the succeeding Raman pulse generation.
Fig. 3. Output characteristics of the amplified DSR pulse. (a) Output average power versus the pump power. (b) At 6.15 W pump power, amplified pulse energy and peak power versus DSR’s pulse duration (inset: the comparison of DSR temporal profiles before and after the amplification, note: the pulse duration is 10.25 ns).
3.2 Efficient Raman pulse generation
In the experiment, the dependence of the first-order Raman spectrum evolution on the pulse duration of the DSR at the maximum peak power was investigated in linear scale, as displayed in Fig. 4(a). Actually, the maximum peak power of the launched DSR at the pulse duration of 2.34 ns∼14.08 ns was decreased to 380 W∼120 W, due to the large coupling loss of ∼19.4% caused by fibers’ mode field mismatch. It is clear that when DSR’s pulse duration is less than 6.7 ns, the dramatically spectral broadening, asymmetry and even distortion will occur. This is caused by the combined effect of SPM, cross-phase modulation (XPM) and pump depletion at a higher pump peak power (>207 W). Meanwhile, the power scaling of Raman pulse was also limited by the lower pump power. In comparison, the DSR with more storage energy and suitable peak power achieved an efficient energy transfer, when its pulse duration was tuned to 9.7 ns and 11.17 ns. At the pulse duration of >11.17 ns, the pump residual was excessive and the amplitude of Raman peak degraded significantly. It illustrated that DSR’s available peak power by this time was not enough to support the maximization of pump-to-Raman conversion. The result indicates that a trade-off between the pulse energy and the peak power of the DSR is essential to optimal pump-to-Raman conversion. In essence, this is also a balance on the limitation of Raman gain saturation and the maximization of pump depletion during the first-order Raman emission buildup [32]. Therefore, by carefully adjusting DSR’s pulse duration and peak power, we eventually found that more efficient Raman conversion was promising when the pump pulse duration was set at 10.25 ns. Based on the amplified spontaneous Raman emission (ASRE) regime in the GeO2-doped fiber, the total output spectra versus pump peak power were displayed in Fig. 4(b). Attributing to the DSR’s steep edges, the SRS was built rapidly from the spontaneous Raman scattering noise. The well-marked first-order Raman shift from 1986.6 nm to 2176.5 nm was observed since the pump peak power exceeded 80 W. The Raman peak intensity almost grew exponentially as the pump peak power increased. According to the spectral distribution in the total output, the first-order Raman component exhibited a spectral purity of up to 96.8% when DSR’s peak power reached 149.4 W. The corresponding spectral FWHM of Raman component was measured to be 24.9 nm. At this point, no higher-order Raman shifts were observed. This suggests that DSR in our laser system enables the nearly complete pump depletion and the most available energy has been transferred to the first-order Raman pulse before the generation of cascaded Raman shifts. To our knowledge, the spectral purity of this Raman pulse pumped by the DSR is the highest among the reports on MIR Raman short pulse fiber lasers till now [17–19].
Fig. 4. Output spectra versus (a) DSR’s pulse duration at maximum incident peak power, (b) incident DSR peak power at 10.25 ns (inset: the spectrum at maximum pump peak power). Note: the noise here refers to the amplified pump noise and the amplified quantum noise that initiates the Raman scattering.
Figure 5(a) demonstrates the laser output power as a function of the incident DSR average power. The average power of Raman pulse was obtained by the method of spectral integration since no befitting bandpass filter could help to extract it from the overall output signal. It is obvious that approximately 0.74 W incident power is required to initiate the first-order Raman shift. As the incident power increased, the output power of the first-order Raman pulse would increase rapidly until the Raman gain got saturated. When the pump power reached 1.325 W, the maximum Raman conversion efficiency of 67.4% and the Raman average power of 0.893 W were achieved in the total output of 0.923 W. In this case, the Raman pulse energy was calculated to be ∼1.03 µJ, according to the repetition rate of 865.1 kHz. At the maximum pump power (1.325 W), the temporal profile of the overall output pulse including a small amount of residual pump was recorded in Fig. 5(b). The output pulse has a broad pedestal and a narrow spike on its trailing edge, which is resulted from a combination of group-velocity dispersion (GVD) and XPM [33]. In theory, for the dispersion-less case, the Raman pulse shape will be consistent with the pump temporal profile [34]. However, in the normal GVD regime, the Raman pulse propagated faster than the pump pulse along the fiber [35]. As a result, the XPM-induced strong chirp was imposed eventually on the trailing edge of the Raman pulse [36–38]. This gave rise to the asymmetric temporal changes and the spike feature as seen in Fig. 5(b). Since the ratio of the DSR residual over the total output has been less than 3.2%, it can be deduced that the spike was dominated by Raman pulse according to the wavelength dependence of the intensity. Owing to the noise shaping before the initiation of the second-order Raman pulse [39], the Raman-dominated spike exhibits a Gaussian profile. Its FWHM is estimated to be 1.18 ns, which is far narrower than initial pump pulse duration. Because of the asymmetric temporal profile, the genuine Raman pulse duration cannot be characterized accurately by the FWHM. Consequently, the corresponding pulse peak power was not obtained.
Fig. 5. (a) The average powers of residual DSR and noise, the first-order Raman pulse, the total output. (b) The total output temporal profile at the maximum pump power. Note: the noise here refers to the amplified pump noise and the amplified quantum noise that initiates the Raman scattering.
In this work, the effectiveness of DSR in the improvement of pump-to-Raman conversion performance was validated successfully. Meanwhile, we achieved the first-order Raman pulse with high spectral purity at 2.177 µm. Comparing to the cases pumped by electrically gain-modulated and actively Q-switched pulses [17,18], our DSR-based Raman fiber laser system is free from the external modulators and the pulse-shaping elements to control the pump. This largely helped to simplify the system constructure and reduce the fabricating cost. In addition, the Raman pulse possesses a large pulse energy at the repetition rate near MHz level. Higher repetition rate can be obtained by adjusting the cavity length or exciting the harmonic mode-locking operation under the DSR condition [40]. As a result, it has great potential for the practical applications including optical frequency comb, high-speed optical sampling, precision metrology in the MIR spectral region. The further power scaling and wavelength extension of efficient Raman pulses could be realized, by building a DSR-based multistage amplifier and adopting novel nonlinear fibers with higher Raman gain and larger Raman shifting amount.
4. Conclusion
In conclusion, we explored the effectiveness of DSR pulse as the pump on generating MIR Raman nanosecond pulse in an all-fiber laser system. Exploiting the ASRE regime in 45 m Ge-core highly nonlinear silica fiber, a significant first-order Raman shift from 1.987 µm to 2.177 µm was generated at the repetition rate of 865.1 kHz. The first-order Raman component presented a spectral purity of up to 96.8% over the entire output spectrum, indicating that the most DSR’s available energy has been transferred successfully. In this case, the maximal pump-to-Raman conversion efficiency of 67.4% was obtained, corresponding to the Raman output power of 0.893 W and pulse energy of 1.03 µJ. Due to the combined effect of GVD and XPM, the output pulse presented an asymmetric temporal profile with a broad pedestal and a narrow Raman-dominated spike on its trailing edge. The further power scaling and the wavelength extension of MIR Raman pulses based on the DSR pumping could resort to a multistage amplifier or the novel nonlinear fibers which is also our following work.
Funding
National Natural Science Foundation of China (61421002, 62005040, U20A20210); Fundamental Research Funds for the Central Universities (ZYGX2019Z012, ZYGX2020KYQD003, ZYGX2021YGCX014); Sichuan Province Science and Technology Support Program (21YYJC2977).
Acknowledgments
We would like to thank Yazhou Wang for the discuss and the advice on the design of our DSR-based Tm-doped fiber ring oscillator.
Disclosures
The authors declare that there are no conflicts of interest related to this article.
Data availability
Data underlying the results presented in this paper are not publicly available at this time but may be obtained from the authors upon reasonable request.
References
1. M. Yumoto, N. Saito, T. Lin, R. Kawamura, A. Aoki, Y. Izumi, and S. Wada, “High-energy, nanosecond pulsed Cr: CdSe laser with a 2.25-3.08 µm tuning range for laser biomaterial processing,” Biomed. Opt. Express 9(11), 5645–5653 (2018). [CrossRef]
2. S. Wolf, T. Trendle, J. Kiessling, J. Herbst, K. Buse, and F. Kühnemann, “Self-gated mid-infrared short pulse upconversion detection for gas sensing,” Opt. Express 25(20), 24459–24468 (2017). [CrossRef]
3. H. H. P. T. Bekman, J. C. van den Heuvel, F. J. M. van Putten, and R. Schleijpen, “Development of a mid-infrared laser for study of infrared countermeasures techniques,” Proc. SPIE 5615, 27–38 (2004). [CrossRef]
4. S. Sato, M. Ogura, M. Ishihara, S. Kawauchi, T. Arai, T. Matsui, A. Kurita, M. Obara, M. Kikuchi, and H. Ashida, “Nanosecond, high-intensity pulsed laser ablation of myocardium tissue at the ultraviolet, visible, and near-infrared wavelengths: In-vitro study,” Lasers Surg. Med. 29(5), 464–473 (2001). [CrossRef]
5. W. Yao, C. Shen, Z. Shao, Q. Liu, H. Wang, Y. Zhao, and D. Shen, “High-power nanosecond pulse generation from an integrated Tm-Ho fiber MOPA over 2.1 µm,” Opt. Express 26(7), 8841–8848 (2018). [CrossRef]
6. H. Luo, F. Liu, J. Li, and Y. Liu, “High repetition rate gain-switched Ho-doped fiber laser at 2.103 µm pumped by h-shaped mode-locked Tm-doped fiber laser at 1.985 µm,” Opt. Express 26(20), 26485–26494 (2018). [CrossRef]
7. Y. Wang, H. Luo, H. Wu, J. Li, and Y. Liu, “Tunable pulsed dysprosium laser within a continuous range of 545 nm around 3 µm,” J. Lightwave Technol. 40(14), 4841–4847 (2022). [CrossRef]
8. H. Luo, J. Yang, J. Li, and Y. Liu, “Widely tunable passively Q-switched Er3+-doped ZrF4 fiber laser in the range of 3.4-3.7 µm based on a Fe2+: ZnSe crystal,” Photonics Res. 7(9), 1106–1111 (2019). [CrossRef]
9. R. H. Stolen, E. P. Ippen, and A. R. Tynes, “Raman oscillation in glass optical waveguide,” Appl. Phys. Lett. 20(2), 62–64 (1972). [CrossRef]
10. J. Liu, F. Tan, H. Shi, and P. Wang, “High-power operation of silica-based Raman fiber amplifier at 2147 nm,” Opt. Express 22(23), 28383–28389 (2014). [CrossRef]
11. V. Fortin, M. Bernier, D. Faucher, J. Carrier, and R. Vallée, “3.7 W fluoride glass Raman fiber laser operating at 2231 nm,” Opt. Express 20(17), 19412–19419 (2012). [CrossRef]
12. J. Dong, L. Zhang, H. Jiang, X. Yang, W. Pan, S. Cui, X. Gu, and Y. Feng, “High order cascaded Raman random fiber laser with high spectral purity,” Opt. Express 26(5), 5275–5280 (2018). [CrossRef]
13. M. Bernier, V. Fortin, M. El-Amraoui, Y. Messaddeq, and R. Vallée, “3.77 µm fiber laser based on cascaded Raman gain in a chalcogenide glass fiber,” Opt. Lett. 39(7), 2052–2055 (2014). [CrossRef]
14. J. Gauthier, M. Olivier, P. Paradis, M. Dumas, M. Bernier, and R. Vallée, “Femtosecond tunable solitons up to 4.8 µm using soliton self-frequency shift in an InF3 fiber,” Sci. Rep. 12(1), 15898–14 (2022). [CrossRef]
15. F. Wang, X. Zhou, X. Zhang, X. Yan, S. Li, T. Suzuki, Y. Ohishi, and T. Cheng, “Mid-infrared cascaded stimulated Raman scattering and flat supercontinuum generation in an As-S optical fiber pump at 2 µm,” Appl. Opt. 60(22), 6351–6356 (2021). [CrossRef]
16. Y. Jiao, Z. Jia, X. Guo, Z. Zhao, Y. Ohishi, W. Qin, and G. Qin, “Third-order cascaded Raman shift in all-solid fluorotellurite fiber pumped at 1550 nm,” Opt. Lett. 47(3), 690–693 (2022). [CrossRef]
17. P. T. Rakich, Y. Fink, and M. Soljačić, “Efficient mid-IR spectral generation via spontaneous fifth-order cascaded-Raman amplification in silica fibers,” Opt. Lett. 33(15), 1690–1692 (2008). [CrossRef]
18. H. Jiang, L. Zhang, and Y. Feng, “Silica-based fiber Raman laser at >2.4 µm,” Opt. Lett. 40(14), 3249–3252 (2015). [CrossRef]
19. H. Jiang, L. Zhang, X. Yang, T. Yu, and Y. Feng, “Pulsed amplified spontaneous Raman emission at 2.2 µm in silica-based fiber,” Appl. Phys. B 122(4), 74 (2016). [CrossRef]
20. T. Du, Y. Li, H. Wang, Z. Chen, V. M. Mashinsky, and Z. Luo, “2166 nm all-fiber short-pulsed Raman laser based on germania-core fiber,” Opt. Express 27(24), 34552–34558 (2019). [CrossRef]
21. K. K. Chen, S. Alam, P. Horak, C. A. Codemard, A. Malinowski, and D. J. Richardson, “Excitation of individual Raman Stokes lines in the visible regime using rectangular-shaped nanosecond optical pulses at 530 nm,” Opt. Lett. 35(14), 2433–2435 (2010). [CrossRef]
22. D. Lin, S. Alam, P. S. Teh, K. K. Chen, and D. J. Richardson, “Tunable synchronously-pumped fiber Raman laser in the visible and near-infrared exploiting MOPA-generated rectangular pump pulses,” Opt. Lett. 36(11), 2050–2052 (2011). [CrossRef]
23. Z. Sacks, O. Gayer, E. Tal, and A. Arie, “Improving the efficiency of an optical parametric oscillator by tailoring the pump pulse shape,” Opt. Express 18(12), 12669–12674 (2010). [CrossRef]
24. G. Aoust, A. Godard, M. Raybaut, O. Wang, J.-M. Melkonian, and M. Lefebvre, “Optimal pump pulse shapes for optical parametric oscillators,” J. Opt. Soc. Am. B 33(5), 842–849 (2016). [CrossRef]
25. F. Ghiringhelli, L. M. B. Hickey, and M. N. Zervas, “Adaptive pulse shape control in a diode-seeded nanosecond fiber MOPA system,” Opt. Express 14(23), 10996–11001 (2006). [CrossRef]
26. A. Malinowski, P. Gorman, C. A. Codemard, F. Ghiringhelli, A. J. Boyland, A. Marshall, M. N. Zervas, and M. K. Durkin, “High-peak-power, high-energy, high-average-power pulsed fiber laser system with versatile pulse duration and shape,” Opt. Lett. 38(22), 4686–4689 (2013). [CrossRef]
27. L. Liu, J. H. Liao, Q. Y. Ning, W. Yu, A. P. Luo, S. H. Xu, Z. C. Luo, Z. M. Yang, and W. C. Xu, “Wave-breaking-free pulse in an all-fiber normal-dispersion Yb-doped fiber laser under dissipative soliton resonance condition,” Opt. Express 21(22), 27087–27092 (2013). [CrossRef]
28. Z. Luo, W. Cao, Z. Lin, Z. Cai, A. Luo, and W. Xu, “Pulse dynamics of dissipative soliton resonance with large duration-tuning range in a fiber ring laser,” Opt. Lett. 37(22), 4777–4779 (2012). [CrossRef]
29. Z. Zheng, D. Ouyang, X. Ren, J. Wang, J. Pei, and S. Ruan, “0.33 mJ, 104.3 W dissipative soliton resonance based on a figure-of-9 double-clad Tm-doped oscillator and an all-fiber MOPA system,” Photonics Res. 7(5), 513–517 (2019). [CrossRef]
30. G. Chen, C. Gu, L. Xu, H. Zheng, and H. Ming, “Simulation of nanosecond square pulse fiber laser based on nonlinear amplifying loop mirror,” Chin. Opt. Lett. 9(9), 091405 (2011). [CrossRef]
31. Y. Lyu, X. Zou, H. Shi, C. Liu, C. Wei, J. Li, H. Li, and Y. Liu, “Multipulse dynamics under dissipative soliton resonance conditions,” Opt. Express 25(12), 13286–13295 (2017). [CrossRef]
32. C. Yijiang and A. W. Snyder, “Saturation and depletion effect of Raman scattering in optical fibers,” J. Lightwave Technol. 7(7), 1109–1117 (1989). [CrossRef]
33. M. Santagiustina, P. Balan, and C. D. Angelis, “Combined effects of self-, cross-phase modulation and stimulated Raman scattering in optical fibers,” Opt. Commun. 100(1-4), 197–203 (1993). [CrossRef]
34. B. I. Carman, F. Shimizu, C. S. Wang, and N. Bloembergen, “Theory of Stokes pulse shapes in transient stimulated Raman scattering,” Phys. Rev. A 2(1), 60–72 (1970). [CrossRef]
35. G. P. Agrawal, Nonlinear Fiber Optics (Elsevier, 2013), Chap.1.
36. D. Schadt and B. Jaskorzynska, “Frequency chirp and spectra due to self-phase modulation and stimulated Raman scattering influenced by pulse walk-off in optical fibers,” J. Opt. Soc. Am. B 4(5), 856–862 (1987). [CrossRef]
37. G. P. Agrawal, “Modulation instability induced by cross-phase modulation in optical fibers,” Phys. Rev. A 39(7), 3406–3413 (1989). [CrossRef]
38. J. T. Manassah, “Induced phase modulation of the stimulated Raman pulse in optical fibers,” Appl. Opt. 26(18), 3747–3749 (1987). [CrossRef]
39. E. Landahl, D. Baiocchi, and J. R. Thompson, “A simple analytic model for noise shaping by an optical fiber Raman generator,” Opt. Commun. 150(1-6), 339–347 (1998). [CrossRef]
40. G. Semaan, A. Niang, M. Salhi, and F. Sanchez, “Harmonic dissipative soliton resonance square pulses in an anomalous dispersion passively mode-locked fiber ring laser,” Laser Phys. Lett. 14(5), 055401 (2017). [CrossRef]
