Open Access
Add to BibSonomy
Abstract
We firstly report a high pulse repetition rate (101.4 MHz) nonlinear post-compression based on the normal dispersion fiber (NDF) operating in 2-µm wavelength region. With only one-stage NDF-based nonlinear pulse compressor, the 2-µm ultrafast laser pulses are compressed from ∼460 fs down to 70 fs, corresponding to ∼10.4 optical oscillation cycle. With two-stage nonlinear pulse compressor, the input ultrafast laser pulses are further compressed to 28.3 fs (∼4.3 optical oscillation cycle). In each case, the average power of the compressed 2-µm laser pulses exceeds 1 W, which is believed to be the highest average power never achieved at ∼100-MHz pulse repetition rate. The efficiencies of the one-stage and two-stage nonlinear pulse compressors are 64% and 47% respectively.
© 2023 Optica Publishing Group under the terms of the Optica Open Access Publishing Agreement
1. Introduction
2-µm ultrafast fiber lasers have wide application fields, such as the gas detection [1], industrial material processing [2–4], medical surgery [5] and driving mid-IR OPO or OPA [6]. Especially, few-cycle 2-µm laser pulses enable to drive the water-window X-ray tabletop coherent light source [7] and realize the generation of attosecond coherent light pulse [8]. Up to now, the shortest pulse duration directly generated from the 2-µm mode-locking fiber oscillator is limited around ∼50-fs (∼7.5 cycle) with an average power of only tens of milliwatts [9]. Using nonlinear pulse amplification can increase the average power of 2-µm ultrafast laser pulse, but could not fully conquer the spectrum narrowing effect, which results in a long laser pulse duration at the level of sub-hundred or even few hundred femtoseconds [10–12], hardly to reach ten optical oscillation cycles regime or below.
Nonlinear pulse compression, relying on nonlinear spectrum broadening process in the gas-filled hollow core fiber (HCF) or highly nonlinear fiber (HNLF) of a fiber ultrafast laser, has been proven to be an efficient way to realize few-cycle laser pulse [13,14]. Figure 1 summarizes the previously reported nonlinear pulse compressors operating in the 2-µm wavelength region, which are based on either gas-filled HCF or HNLF. With the HCF, the achieved shortest pulse duration is 4.5 fs [15] and the average power has exceeded 100 W [16]. The efficiencies of the HCF-based nonlinear pulse compressors are mostly above 50% (see Fig. 1(c)). While the requirement of a large pulse energy mainly in the millijoule level for efficient spectrum broadening in the nonlinearity noble gas makes the input pulse repetition rate below megahertz (MHz) level (see Fig. 1(d)). Due to the relatively large nonlinearity, the HNLF is applicable for the nonlinear pulse compression of small energy pulse with a high pulse repetition. Basically, there are two types of HNLF, which are respectively featured with a large mode field diameter (MFD) of >10-µm and a small MFD of <4-µm. Just as the HCF, the former one requires input laser pulse with the pulse energy of microjoule level when being used in the nonlinear pulse compressor (see Fig. 1(d)). Using the large MFD-HNLF, the shortest pulse duration of 13 fs [21] (see Fig. 1(a)) and the highest average power of 24.5 W have been realized with a high pulse compression ratio close to 18 [22] (see Fig. 1(b)). The efficiencies of the large MFD-HNLF based nonlinear pulse compressors are large than 60% (see Fig. 1(c)). Small MFD-HNLF is suitable for the nonlinear pulse compression of nanojoule input laser pulse with a high repetition rate up to hundreds of MHz level. Utilizing one-stage small MFD-HNLF, the highest pulse repetition rate of 500-MHz is realized with a pulse duration of 58-fs [23]. The highest efficiency of 82% has been realized in a 100-MHz one-stage small MFD-HNLF nonlinear pulse compressor [24]. Multi-stage nonlinear pulse compressions with small MFD-HNLF are also reported, for example, the 27-fs 2-µm laser pulses with 80-MHz pulse repetition rate are generated with the efficiency of 60% by employing triple-stage small MFD-HNLF-based nonlinear pulse compressor [25].
Fig. 1. The summarized results of the fiber nonlinear pulse compressors in 2-µm wavelength region [16–29]. HNLF: highly nonlinear fiber, HCF: hollow core fiber, NDF: normal dispersion fiber, MFD: mode field diameter. Pulse compression ratio: the ratio between the pulse duration of the input laser pulse and that of the compressed laser pulse. Pink line: average power.
Although the small MFD-HNLF is suitable for nonlinear compression of high repetition rate pulses, it suffers from a low laser damage threshold, which limits the average output power to only milliwatt-level (see Fig. 1(d)). Besides that, the small MFD-HNLF based nonlinear pulse compressor shows a pulse compression ratio less than 6-times (see Fig. 1(b)), hindering the direct generation of few-cycle laser pulse from a relatively long input laser pulse. Moreover, the high fabrication cost of HCF and HNLF is also unfavorable for their wide applications in the 2-µm wavelength region. It is well known that the normal dispersion fiber (NDF) is usually employed for dispersion compensation of the ultrafast laser pulse in 2-µm wavelength region [30]. In order to increase the value of positive group velocity dispersion (GVD) in the NDF, the core diameter of the NDF is drastically reduced, which gives it the possibility to increase the intensity of the transmitted ultrafast laser pulse thus strengthen the optical nonlinearity compared with the standard 2-µm single mode fiber. Besides, the positive GVD of the NDF could ensure a strong interpulse coherence of the transmitted ultrafast pulse by avoiding pulse splitting effect, which is typically observed in the single-mode fiber when the self-phase modulation effect occurs in the negative GVD environment [31]. So it is expected to use NDF with a low cost and relatively high damage threshold to nonlinearly compress the high repetition ultrafast laser pulse in the 2-µm wavelength region. But to the best of our knowledge, there is no report on the NDF-based nonlinear pulse compressor at this moment.
In this work, the 2-µm ultrafast laser pulses with the pulse duration of ∼460 fs and a pulse repetition rate of 101.4 MHz are post compressed to 70 fs and further to 28.3 fs by using one- and two-stage NDF-based nonlinear pulse compressors, respectively. The average powers of the compressed 2-µm laser pulses all exceed 1 W, which are believed to be the highest average power never achieved at the pulse repetition rate of ∼100-MHz. The efficiencies of the one-stage and two-stage nonlinear pulse compressors are 64% and 47%, respectively.
2. Experimental results and discussion
Figure 2 presents the schematic diagram of one-stage NDF-based nonlinear pulse compressor. The 101.4-MHz driving laser pulse with the highest average power of 2.14 W is delivered from a Tm-doped fiber chirped pulse amplification (CPA) laser system, in which the 460-fs seed pulse is output from the nonlinear polarization rotation-based Tm-doped fiber mode-locking oscillator. The laser spectrum of the driving laser pulse is centered at 2012nm (see gray line in Fig. 3(b)). The shortest pulse duration of the ultrafast driving laser pulse is 436 fs at the maximum average power, which approaches to the Fourier transform limited (FTL) laser pulse of ∼425 fs. The pulse duration of the input ultrafast laser pulse is adjusted with a grating pair-based pulse compressor. The incident laser beam is collimated and feed into the nonlinear pulse compressor with a fiber collimator after transmitting through a half-wave plate. The one-stage nonlinear pulse compressor consists of a 30-cm long NDF (Nufern, SM2000D) used for spectrum broadening, a 19-cm long polarization maintaining (PM) single-mode fiber (Nufern, PM-SMF-10/130) and a 15-cm long standard single-mode fiber (Corning, SMF-28), which serve as pigtails of the collimators. The parameters of the employed fibers are listed in Table 1 below. Followed the NDF, another collimator is employed for coupling out of the ultrafast laser pulse. A pair of chirped mirror is employed for dispersion compensation of the laser pulse. The chirped mirror has the reflectivity of >99.9% at the wavelength ranging from 2000 to 2200 nm and provides the group delay dispersion (GDD) of -1000 fs2 for the reflected laser pulse. The optical spectrum and the pulse duration of the laser pulse are respectively measured with a spectrometer (APE, WaveScan USB) and an auto-correlator (APE, pulseCheck). The output power is recorded with a power-meter (Thorlabs, S425C).
Fig. 2. The schematic diagram of one-stage NDF-based nonlinear pulse compressor. λ/2: half-wave plate, PMF: polarization maintaining fiber, NDF: normal dispersion fiber, SMF: single-mode fiber.
Fig. 3. (a) The spectral evolution versus output power after the ultrafast laser pulse experiencing one-stage nonlinear pulse compressor. (b) The output spectrum in the linear and log- (inset) coordinates (red line) at the maximum output power. The laser spectrum of the incident laser pulse (gray line).
Table 1. The parameters of the employed fibers in the 2-µm nonlinear pulse compressor
Initially, the ultrafast driving laser pulse is up-chirped from 436 fs to ∼470 fs by introducing a positive group delay dispersion (GDD) of +28000 fs2 before going into the followed nonlinear pulse compressor. An up-chirp input laser pulse could balance the PM fiber-introduced anomalous dispersion of -18000 fs2, making sure a near FTL laser pulse goes into the NDF thus for enhancing the spectrum broadening effect. In the NDF, both of the self-phase modulation effect and the NDF result in an up-chirp for the transmitted laser pulses, which has to introduce a negative GDD for post dispersion compensation. The pigtail of the output fiber collimator can partly compensate a part of the positive GDD in the laser pulse. The large residual GDD about +12000 fs2 is compensated with a pair of chirped mirror. The measured output spectra at different output powers are shown in Fig. 3(a) below. It shows that as the output power increases, the laser spectrum is extended to cover the wavelength range from 1900nm to 2100 nm, which is about 8-times broader than that of the incident ultrafast laser pulse (see Fig. 3(b)). The spectral asymmetry attributes to the nonlinear optical process (mainly the self-phase modulation) inside the nonlinear pulse compressor. The inset of Fig. 3(b) shows the spectral range is almost symmetrically broadened inside the nonlinear pulse compressor. The maximum output power of the nonlinear compressed pulses is 1.38 W, corresponding to ∼64% of the total input power of the laser pulses. The efficiency of the one-stage nonlinear pulse compressor approaches to the most reported values of the one-stage nonlinear pulse compressors in Fig. 1(c). The large loss mainly arises from the ∼7.8% coupling loss of the fiber collimator and the ∼27.6% mode-mismatching loss between different type fibers. The pulse energy of the compressed laser pulse is 13.6 nJ, which is ∼2 times larger than the reported highest value of 5.6 nJ in the >100-MHz pulse repetition rate regime [25].
Figure 4(a) gives the output power versus the pulse duration. The pulse duration of the output laser pulse is decreasing with the increase of the output power. Once the output power exceeds 0.8 W, the laser pulse is unable to be further shortened, which is limited by the weak spectrum broadening effect. The limitation of spectrum broadening arises from the restricted pulse peak power, which can’t be further enhanced, because the accumulated large up-chirp of the self-phase modulation and the normal dispersion in the NDF greatly stretches the laser pulse duration. The FTL laser pulse is determined to be 65 fs (dashed line in Fig. 4(c)) by assuming the zero dispersion of the measured spectrum at the maximum output power (Fig. 3(b)). The GDD and third order dispersion (TOD) are introduced into the FTL laser pulse to make the calculated autocorrelation trace (dashed line in Fig. 4(b)) match well with the measured result (solid line in Fig. 4(b)). So the residual GDD, TOD, and the pulse profile of the compressed laser pulse can be retrieved. The red solid line in Fig. 4(b) is the measured autocorrelation trace at the highest output power, which is close to the calculated result (dashed line) by assuming a residual GDD of zero and TOD of +4.4 × 105 fs3. The solid line in Fig. 4(c) shows the reconstructed laser pulse with a pulse duration of 70 fs, approaching to the FTL value of 65 fs (dashed line). The pulse compression ratio is ∼6.7 with the pulse peak power increasing from 48 kW to 194 kW. The uncompensated high-order dispersion manifest itself as a pulse tail around the main pulse, accounting to ∼6.7% of the total pulse energy.
Fig. 4. (a) The pulse duration evolution versus output power after the ultrafast laser pulse experiencing one-stage nonlinear pulse compressor. (b) The measured autocorrelation trace (solid line) and the calculated result (dashed line) by assuming a FTL pulse at the maximum output power. (c) The reconstructed laser pulse (solid line) and FTL pulse (dashed line).
As mentioned above, in the one-stage NDF-based nonlinear pulse compressor, the restriction of the pulse peak power limits the spectrum to be further broadened. Just increasing the length of the NDF can’t further shorten the pulse duration to below 70 fs. In order to increase the peak power of the ultrafast laser pulse, a 40-cm long SMF (SMF1) is fused behind NDF (NDF1) for narrowing the pulse duration by introducing a negative GDD of -32400 fs2. Moreover, another 20-cm long NDF (NDF2) is employed for further spectrum broadening of the ultrafast laser pulse. The schematic diagram of the two-stage NDF-based nonlinear pulse compressor is shown in Fig. 5. The total dispersion provided by NDF1 and NDF2 is +68500 fs2. After NDF2, the residual positive GDD of +23000 fs2 in the ultrafast laser pulse is compensated by the followed 14-cm long SMF2 and the chirped mirror pair, which respectively provide negative dispersion of -11000 fs2 and -12000 fs2. The pulse duration of the driving laser pulse is reduced from 470 fs to 450 fs for enhancing the self-phase modulation effect inside the two-stage nonlinear pulse compressor. The 450-fs laser pulse has the residual up-chirp about +18000 fs2 compared with the initial 436-fs laser pulse from the CPA laser system.
Fig. 5. The schematic diagram of two-stage NDF-based nonlinear pulse compressor. λ/2: half-wave plate, PMF: polarization maintaining fiber, NDF: normal dispersion fiber, SMF: single-mode fiber.
Figure 6(a) shows the output spectrum versus average output power. Due to the enhanced nonlinear process, the range of the laser spectrum is increasing as the increase of the output power. The maximum output power is 1.02 W, corresponding to ∼47% of the total input average power, which is lower than that (60%) of the reported all-fiber cascaded-stage nonlinear pulse compressor [25]. The reduced efficiency mainly attributes to the additional ∼7.8% coupling loss of the fiber collimator. The red solid line in Fig. 6(b) is the broadened laser spectrum measured at the maximum average output power from the two-stage NDF-based nonlinear pulse compressor, which covers a spectrum range of 320 nm ranging from 1850nm to 2170 nm. Compared with the spectrum obtained from nonlinear pulse compressor comprising only one-stage NDF, which covers from 1900nm to 2100 nm, the spectrum range further broadens about 1.6 times. The relatively large spectral intensity in the longer wavelength region arises from the enhancement of the nonlinear optical process. The log plot in Fig. 6(b) shows the spectrum broadening is dominated by self-phase modulation inside the two-stage nonlinear pulse compressor. The spikes on the top of the broadened spectrum mainly attribute to the enhanced self-phase modulation effect and the PMF-induced birefringence filtering effect.
Fig. 6. (a) The spectral evolution versus output power after the ultrafast laser pulse experiencing the two-stage nonlinear pulse compressor. (b) The output spectrum at the maximum output power in the linear and log- (inset) coordinates (red line). The output spectrum of the one-stage nonlinear pulse compressor at the maximum output power (gray line). NPC: nonlinear pulse compressor.
Figure 7(a) shows the compressed ultrafast pulse duration versus the average output power. Due to the broadened spectrum as shown in Fig. 6(a), the compressed pulse duration decreases as the increase of the output power. The measured autocorrelation trace (solid line in Fig. 7(b)) is close to the calculated result (dashed line in Fig. 7(b)) by assuming a FTL pulse at the highest output power. The reconstructed laser pulse (solid line) is shown in Fig. 7(c), indicating a pulse duration of 28.3 fs, approaching to the FTL value of 25.1 fs (dashed line). The total pulse compression ratio with two-stage NDFs is ∼16, which is about 3-times large than the highest value of 5.8 realized by the small MFD-HNLF-based nonlinear pulse compressor (see Fig. 1(b)). The pulse peak power is enhanced 7.3-times to ∼353 kW compared with the incident laser pulse. The pedestal of the compressed laser pulse accounts to ∼24% of total pulse energy, which is large than the 6.7% of the one-stage nonlinear pulse compressor. The increased pedestal energy is believed to mainly arise from the high-order dispersion of the longer fiber and the optical nonlinearity-induced phase distortion inside the two-stage nonlinear pulse compressor.
Fig. 7. (a) The pulse duration evolution versus output power after the ultrafast laser pulse experiencing two-stage nonlinear pulse compressor. (b) The measured autocorrelation trace (solid line) and the calculated result (dashed line) by assuming a FTL pulse at the maximum output power. (c) The reconstructed laser pulse (solid line) and FTL pulse (dashed line).
3. Conclusion and outlooks
In this work, we realize the nonlinear post-compression for the 2-µm ultrafast laser pulse with a pulse repetition rate of ∼101-MHz by using the NDF-based nonlinear pulse compressors. Based on the one- and two-stage NDF-based nonlinear pulse compressors, the laser pulses with the pulse duration of 70 fs and 28.3 fs are respectively realized. In both cases, the average output powers are always higher than 1 W, which is believed to be the highest power achieved for >100-MHz pulse repetition rate. The experimental results demonstrate the NDF-based nonlinear post-compression has significant advantages in realizing the nonlinear compression of high repetition rate laser pulse. The proposed method is believed to be applicable for the nonlinear pulse compression in other wavelength regions. Besides that, the pulse duration is expected to be further shortened with the NDF-based all polarization-maintaining fiber nonlinear pulse compressor, which relies on the higher nonlinear coefficient of the polarized light than that of the circularly polarized light.
Funding
High-level Talent Cultivation Funds of State Key Laboratory of Crystal Materials of Shandong University (Kejian Yang); Taishan Scholar Foundation of Shandong Province (tsqn201812010); Qilu Young Scholar Program of Shandong University (Tianli Feng); Natural Science Foundation of Shandong Province (ZR2020QF096); National Natural Science Foundation of China (62005144, 61775119, 62175128).
Disclosures
The authors declare no conflicts of interest.
Data availability
Date 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. A. Pal, S. Y. Chen, R. Sen, T. Sun, and K. T. V. Grattan, “A high-Q low threshold thulium-doped silica microsphere laser in the 2 µm wavelength region designed for gas sensing applications,” Laser Phys. Lett. 10(8), 085101 (2013). [CrossRef]
2. B. Voisiat, D. Gaponov, P. Gečys, L. Lavoute, M. Silva, A. Hideur, N. Ducros, and G. Račiukaitis, “Material processing with ultra-short pulse lasers working in 2 µm wavelength range,” Proceedings of SPIE - The International Society for Optical Engineering · March 2015.
3. J. Geng, X. Fang, L. Zhang, G. Yao, L. Xu, F. Liu, W. Tang, L. Shi, and M. Qiu, “Controllable generation of large-scale highly regular gratings on Si films,” Light: Advanced Manufacturing 2(3), 273–282 (2021). [CrossRef]
4. J. Geng, W. Yan, L. Shi, and M. Qiu, “Surface plasmons interference nanogratings: wafer-scale laser direct structuring in seconds,” Light: Sci. Appl. 11(1), 189 (2022). [CrossRef]
5. N. M. Fried and K. E. Murray, “High-power thulium fiber laser ablation of urinary tissues at 1.94 µm,” J. Endourol. 19(1), 25–31 (2005). [CrossRef]
6. Q. Fu, L. Xu, S. Liang, P. C. Shardlow, D. P. Shepherd, S. Alam, and D. J. Richardson, “High-average-power picosecond mid-infrared OP-GaAs OPO,” Opt. Express 28(4), 5741–5748 (2020). [CrossRef]
7. T. Popmintchev, M. C. Chen, D. Popmintchev, P. Arpin, S. Brown, S. Ališauskas, G. Andriukaitis, T. Balčiunas, O. D. Mücke, A. Pugzlys, A. Baltuška, B. Shim, S. E. Schrauth, A. Gaeta, C. Hernández-García, L. Plaja, A. Becker, A. Jaron-Becker, M. M. Murnane, and H. C. Kapteyn, “Bright Coherent Ultrahigh Harmonics in the keV X-ray Regime from Mid-Infrared Femtosecond Lasers,” Science 336(6086), 1287–1291 (2012). [CrossRef]
8. C. Zhang, G. Vampa, D. M. Villeneuve, and P. B. Corkum, “Attosecond lighthouse driven by sub-two cycle, 1.8µm laser pulses,” J. Phys. B: At. Mol. Opt. Phys. 48(6), 061001 (2015). [CrossRef]
9. Y. Nomura and T. Fuji, “Sub-50-fs pulse generation from thulium-doped ZBLAN fiber laser oscillator,” Opt. Express 22(10), 12461–12466 (2014). [CrossRef]
10. Z. Ren, F. Slimen, J. Lousteau, N. White, Y. Jung, J. H. V. Price, D. J. Richardson, and F. Poletti, “Compact chirped-pulse amplification systems based on highly Tm3+-doped germanate fiber,” Opt. Lett. 46(13), 3013–3016 (2021). [CrossRef]
11. A. Rampur, Y. Stepanenko, G. Stępniewski, T. Kardaś, D. Dobrakowski, D. M. Spangenberg, T. Feurer, A. Heidt, and M. Klimczak, “Ultra low-noise coherent supercontinuum amplification and compression below 100 fs in an all-fiber polarization-maintaining thulium fiber amplifier,” Opt. Express 27(24), 35041 (2019). [CrossRef]
12. P. Wan, L. Yang, and J. Liu, “High power 2 µm femtosecond fiber laser,” Opt. Express 21(18), 21374–21379 (2013). [CrossRef]
13. E. A. Khazanov, S. Yu Mironov, and G. Mourou, “Nonlinear compression of high-power laser pulses: compression after compressor approach,” Usp. Fiz. Nauk 189(11), 1173–1200 (2019). [CrossRef]
14. M. Nisoli, S. De Silvestri, and O. Svelto, “Generation of high energy 10 fs pulses by a new pulse compression technique,” Appl. Phys. Lett. 68(20), 2793–2795 (1996). [CrossRef]
15. T. Balciunas, C. Fourcade-Dutin, G. Fan, T. Witting, A. A. Voronin, A. M. Zheltikov, F. Gerome, G. G. Paulus, A. Baltuska, and F. Benabid, “A strong-field driver in the single-cycle regime based on self-compression in a kagome fibre,” Nat. Commun. 6(1), 6117 (2015). [CrossRef]
16. Z. Wang, T. Heuermann, M. Gebhardt, M. Lenski, P. Gierschke, R. Klas, C. Jauregui, and J. Limpert, “100W, 1 mJ, few-cycle pulses at 2 µm wavelength,” EPJ Web Conf. 267, 02025 (2022). [CrossRef]
17. M. Gebhardt, C. Gaida, T. Heuermann, F. Stutzki, C. Jauregui, J. Antonio-Lopez, A. Schulzgen, R. Amezcua-Correa, J. Limpert, and A. Tünnermann, “Nonlinear pulse compression to 43 W GW-class few-cycle pulses at 2 µm wavelength,” Opt. Lett. 42(20), 4179–4182 (2017). [CrossRef]
18. M. Gebhardt, C. Gaida, S. Hädrich, F. Stutzki, C. Jauregui, J. Limpert, and A. Tünnermann, “Nonlinear compression of an ultrashort-pulse thulium-based fiber laser to sub-70 fs in Kagome photonic crystal fiber,” Opt. Lett. 40(12), 2770–2773 (2015). [CrossRef]
19. M. Gebhardt, C. Gaida, F. Stutzki, S. Hädrich, C. Jauregui, J. Limpert, and A. Tünnermann, “High average power nonlinear compression to 4 GW, sub-50 fs pulses at 2 µm wavelength,” Opt. Lett. 42(4), 747–750 (2017). [CrossRef]
20. B. E. Schmidt, A. D. Shiner, P. Lassonde, J. Kieffer, P. B. Corkum, D. M. Villeneuve, and F. Légaré, “CEP stable 1.6 cycle laser pulses at 1.8 µm,” Opt. Express 19(7), 6858–6864 (2011). [CrossRef]
21. T. P. Buter, D. Gerz, C. Hofer, J. Xu, C. Gaida, T. Heuermann, M. Gebhardt, L. Vamos, W. Schweinberger, J. A. Gessner, T. Siefke, M. Heusinger, U. Zeitner, A. Apolonski, N. Karpowicz, J. Limpert, F. Krausz, and I. Pupeza, “Watt-scale 50-MHz source of single-cycle waveform-stable pulses in the molecular fingerprint region,” Opt. Lett. 44(7), 1730–1733 (2019). [CrossRef]
22. C. Gaida, M. Gebhardt, F. Stutzki, C. Jauregui, J. Limpert, and A. Tünnermann, “Self-compression in a solid fiber to 24 MW peak power with few-cycle pulses at 2 µm wavelength,” Opt. Lett. 40(22), 5160–5163 (2015). [CrossRef]
23. J. Jiang, C. Mohr, J. Bethge, A. Mills, W. Mefford, I. Hartl, M. E. Fermann, C.-C. Lee, S. Suzuki, T. R. Schibli, N. Leindecker, K. L. Vodopyanov, and P. G. Schunemann, “500 MHz, 58 fs highly coherent Tm fiber soliton laser,”in“Conference on Lasers and Electro-Optics 2012,” Optical Society of America, CCTh5D.7 (2012).
24. S. Xing, D. M. B. Lesko, T. Umeki, A. J. Lind, N. Hoghooghi, T. H. Wu, and S. A. Diddams, “Single-cycle all-fiber frequency comb,” APL Photonics 6(8), 086110 (2021). [CrossRef]
25. R. Herda and A. Zach, “All-fiber generation of few-cycle pulses at 1950nm by triple-stage compression of a Thulium-doped laser system,” Photonics Conference (IPC), IEEE (2013).
26. P. Li, A. Ruehl, U. Grosse-Wortmann, and I. Hartl, “Sub-100 fs passively mode-locked holmium-doped fiber oscillator operating at 2.06 µm,” Opt. Express 39, 6859–6862 (2014). [CrossRef]
27. B. Sun, J. Luo, Y. Zhang, Q. Wang, and X. Yu, “65-fs Pulses at 2µm in a Compact Tm-Doped All-Fiber Laser by Dispersion and Nonlinearity Management,” IEEE Photon. Technol. Lett. 30(4), 303–306 (2018). [CrossRef]
28. J. Wang, W. Lai, K. Wei, K. Yang, H. Zhu, Z. Zheng, C. Guo, S. Ruan, and P. Yan, “Generation of few-cycle pulses from a mode-locked Tm-doped fiber laser,” Opt. Lett. 46(10), 2445–2448 (2021). [CrossRef]
29. S. Xing, A. S. Kowligy, D. M. B. Lesko, A. J. Lind, and S. A. Diddams, “All-fiber frequency comb at 2 µm providing 1.4-cycle pulses,” Opt. Lett. 45(9), 2660–2663 (2020). [CrossRef]
30. W. Ma, D. Zhao, R. Liu, T. Wang, Q. Yuan, H. Xiong, H. Ji, and H. Jiang, “Observation and optimization of 2 µm mode-locked pulses in all-fiber net anomalous dispersion laser cavity,” Opto-Electron. Adv. 3(11), 200001 (2020). [CrossRef]
31. N. Raabe, T. Feng, T. Witting, A. Demircan, C. Brée, and G. Steinmeyer, “Role of Intrapulse Coherence in Carrier-Envelope Phase Stabilization,” Phys. Rev. Lett. 119(12), 123901 (2017). [CrossRef]
