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Reflective carbon nanotube as the saturable absorber for mode-locked 1064 nm laser
Optik 125 (2014) 5666–5668
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Reflective carbon nanotube as the saturable absorber for mode-locked 1064 nm laser Mingwen Fan a , Baomin Ma b , Jie Liu a,∗ , Yonggang Wang c a
College of Physics and Electronics, Shandong Normal University, Jinan 250014, China School of Information Science and Engineering, Shandong University, Jinan 250100, China State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China b c
a r t i c l e
i n f o
Article history: Received 22 October 2013 Accepted 27 May 2014 PACS: 42.55.Xi 42.60.Fc 42.65.Re 42.70.Nq
a b s t r a c t With a reflective single-walled carbon nanotube as the saturable absorber, a laser diode-pumped passively mode-locked Nd:YVO4 laser at 1064 nm was realized for the first time. The pulse duration of 12 ps was produced with a repetition rate of 83.7 MHz. The peak power and the single pulse energy of the mode-locking laser were 1.28 kW and 15.4 nJ, respectively. © 2014 Elsevier GmbH. All rights reserved.
Keywords: Reflective single walled carbon nanotube saturable absorber Mode-locked lasers Nd:YVO4 crystal
1. Introduction All-solid-state passively mode-locked lasers in the infrared spectra have wide applications in spectroscopy, optical communications, material processing, nonlinear frequency translation, medical treatments, etc. [1,2]. Development of new gain media and mode-locked devices has changed the outlook of ultrafast lasers over the past two decades. Particularly, the realization of different mode-locked devices has pushed the applications of ultrafast pulses to a realm broader than ever before. As a relatively traditional mode-locking technique, the semiconductor saturable absorber mirrors (SESAMs) were widely used in the past few years [3]. Nevertheless, current mode-locked technologies still suffer from drawbacks. The fabrication of SESAMs requires complicated deposition techniques and has disadvantages of relatively narrow operational range and long recovery times [4]. These limitations motivate research on new materials, novel designs and technologies [5]. Compared to SESAM, single walled
∗ Corresponding author. Tel.: +86 15264153867. E-mail address: [email protected] (J. Liu). http://dx.doi.org/10.1016/j.ijleo.2014.07.051 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
carbon nanotube saturable absorber (SWCNT-SA) can be fabricated by simple and economy-costed methods, such as spray [6], spin coating [7] or horizontal evaporation methods [8,9]. Additionally, SWCNT-SA has excellent chemical stability, short recovery times and broad spectral range throughout the near-infrared ranges above 1.0 m, which was controlled by varying the tube diameter and its characteristic [10,11]. Recently, the SWCNT-SAs have been widely used for ultrashort pulse generation on the passively mode-locked solid-state lasers [12,13]. SWCNT-SAs can be fabricated as transmission-type and reflection-type. Generally, in comparison with the transmission-type, the reflection-type has less non-saturable loss. The laser gain medium Nd:YVO4 , due to its high absorption coefficient and large stimulated emission cross section, has been proved to be excellent laser material for achieving mode-locked lasers around 1 m [14]. Until now, there are a great number of researches on diode-pumped Nd:YVO4 lasers based on SESAM [15,16] and transmission SWCNT-SA [17–19]. However, there has never been reported on a diode-pumped passively mode-locked Nd:YVO4 laser by a reflective single walled carbon nanotube saturable absorber (RSWCNT-SA). In this paper, by using a RSWCNT-SA as the saturable absorber, a diode-pumped passively mode-locked Nd:YVO4 laser at
M. Fan et al. / Optik 125 (2014) 5666–5668
5667
Fig. 1. Schematic configuration of the W-type cavity.
1 m was realized for the first time. The laser operated at a repetition frequency of 83.7 MHz. A pulse duration of 12 ps was produced with a single pulse energy of 15.4 nJ for a RSWCNT-SA mode-locked laser, and its peak power reached to 1.28 kW.
Fig. 3. (a) Pulse train of the cw mode-locking laser recorded in 10 ns per division time scale. The inset figure (b) corresponds to the pulse train recorded in 1 s per division time scale.
3. Results and discussion 2. Experimental setup A schematic diagram of the experimental apparatus was shown in Fig. 1. The fiber-coupled diode laser was used as the pump source, which had a core-diameter of 400 m and a N.A. of 0.22. The emitting wavelength of the laser diode was 808 nm with the maximum available output power of 30 W. The pump laser was focused on the Nd:YVO4 crystal with a radius of 200 m by 1:1 focus lens. The dimension of Nd:YVO4 crystal with doping concentration of 0.5 at. % was 4 × 4 × 8 mm3 . In the experiment, the laser crystal was mounted in a Cu holder whose temperature was stabilized at 14 ◦ C by circulating water. Laser cavity consisted of three mirrors. The left side of the Nd:YVO4 crystal was coated to be highly reflecting at 1064 nm, and anti-reflecting (AR) at 808 nm pumping wavelength, which also acted as the input mirror. The other side of the crystal was coated for AR at 1064 nm and 808 nm. M1 and M2 were high-reflection coated at 1064 nm with radii of curvature of 200 mm and 800 mm, respectively. The RSWCNT-SA employed here was similar to that in [20], acted as a flat mirror and saturable absorber. We selected the transmission of 3% as the output coupler (OC) with radius of curvature of 200 mm. The length of the folded cavity was 1790 mm. The laser cavity was carefully designed to guarantee a sufficient small mode area in the gain medium and an appropriate operation of RSWCNT-SA in the strong saturation regime within its damage threshold. Using the ABCD-matrix method, we calculated the mode radius at the RSWCNT-SA to be 62 m.
Average output power / W
1.8
The relation of the mode-locked output power versus the absorbed pump power of the laser was shown in Fig. 2. From the drawing, we can see that the laser absorbed pump power threshold was about 0.38 W. Along with the increase of the pump power, Qswitched mode-locked (QML) laser was exhibited first. When the absorbed pump power was greater than 3.54 W, the laser exhibits stable continuous wave (cw) mode-locked operation. When the absorbed pump power was increased to 7.02 W, the average output power of cw mode-locked pulse was 1.78 W with the transverse mode remained as TEM00. It can be seen that the average output power increased linearly with the pump power. No pump saturation was observed, in order to protect the laser crystal from damage, we did not increase the pump power any more. Fig. 3 depicted the cw mode-locked pulse trains detected by a fast photodiode with a rising time of 400 ps (NEW FOCUS 1611) and recorded with a digital storage oscilloscope with 1 GHz bandwidth (Tektronix TDS 5104). Fig. 3(a) was recorded with a time scale of 10 ns/div, while Fig. 3(b) was recorded with a time scale of 1 s/div. It can be seen that the pulse trains are fully modulated with good pulse stability. The pulse repetition was 83.7 MHz, which was in agreement with the cavity length f = c/2L (c is the speed of light, L is the total length of the resonator). From Fig. 3(b), we can see that the pulse train is not plain. We thought the characteristic of the RSWCNT-SA leads to this phenomenon. Fig. 4 illustrated the measured autocorrelation trace corresponding to the absorbed pump power of 4.83 W in the cw mode-locked regime. The pulse width was 12 ps.
Linear Fitting
1.5 1.2 0.9
CWML
QML
0.6 0.3 0.0 0
1
2
3
4
5
6
7
8
Absorbed pump power / W Fig. 2. Variation of the average output power with the absorbed pump power.
Fig. 4. Autocorrelation trace of the pulse with the absorbed pump power of 4.83 W.
5668
M. Fan et al. / Optik 125 (2014) 5666–5668
projects of Shandong Province Science and Technology (Grant No. 2013GGX10108).
Intensity / a.u.
1.0 0.8
References
0.6
=1.6nm
0.4 0.2 0.0 1050
1055
1060
1065
1070
1075
1080
Wavelength / nm Fig. 5. The emission spectrum with the central wavelength of 1064 nm.
Optical spectrum of cw mode-locked laser measured with optical spectrum analyzer (AvaSpec-3648-USB2) was illustrated in Fig. 5. The full width at half maximum (FWHM) of cw mode-locked spectra was measured to be 1.6 nm. The central wavelength was 1064 nm. According to the average output power and pulse repetition rate, the maximum single pulse energy of 15.4 nJ and peak power of 1.28 kW were obtained under the absorbed pump power of 4.83 W. It corresponded to the time–bandwidth product of 5, which was larger than the transform-limited value of 0.314 for sech2 pulses, and indicated that the mode-locked pulses were frequency chirped and their duration could be further narrowed. When the folding angle between each mirror was relatively big, it will generate too many losses in the experiment with the result that we got a relatively wide pulse. The above factor leaded to the larger time–bandwidth product. Therefore, in my opinion, much shorter pulses can be obtained by optimizing the cavity. 4. Conclusions In conclusion, steady state mode-locked operation of a Nd:YVO4 laser is reported with using a RSWCNT-SA for the first time. 1.78 W average output power is obtained at an absorbed pump power of 7.02 W. The laser operates at a repetition frequency of 83.7 MHz with the central wavelength of 1064 nm. The highest pulse energy of 15.4 nJ for a RSWCNT-SA mode-locked laser is obtained, corresponding to its maximum peak power of 1.28 kW. Our experimental results show that the RSWCNT-SA is a promising saturable absorber for mode-locked laser. Acknowledgements This work has been supported by the National Natural Science Foundation of China (Grant No. 61078032) and development
[1] U. Keller, Recent developments in compact ultrafast lasers, Nature 424 (2003) 831–838. [2] U. Keller, Ultrafast solid-state laser oscillators: a success story for the last 20 years with no end in sight, Appl. Phys. B 100 (2010) 15–28. [3] U. Keller, K.J. Weingarten, F.X. Kärtner, D. Kopf, B. Braun, S.D. Jung, R. Fluck, C. Hönninger, N. Matuschek, J. Aus der Au, Semiconductor saturable absorber mirrors (SESAM’s) for femtosecond to nanosecond pulse generation in solid-state lasers, IEEE J. Sel. Top. Quantum Electron. 2 (1996) 435–453. [4] M. Haiml, R. Grange, U. Keller, Optical characterization of semiconductor saturable absorbers, Appl. Phys. B 79 (2004) 331–339. [5] Z. Sun, T. Hasan, A.C. Ferrari, Ultrafast lasers mode-locked by nanotubes and graphene, Phys. E 44 (2012) 1082–1091. [6] Y.W. Song, S. Yamashita, C.S. Goh, S.Y. Set, Passively mode-locked lasers with 17.2-GHz fundamental-mode repetition rate pulsed by carbon nanotubes, Opt. Lett. 32 (2007) 430–432. [7] J.H. Yim, W.B. Cho, S. Lee, Y.H. Ahn, K. Kim, H. Lim, G. Steinmeyer, V. Petrov, U. Griebner, F. Rotermund, Fabrication and characterization of ultrafast carbon nanotube saturable absorbers for solid-state laser mode locking near 1 m, Appl. Phys. Lett. 93 (2008) 161106–161108. [8] M.A. Solodyankin, E.D. Obraztsova, A.S. Lobach, A.I. Chernov, A.V. Tausenev, V.I. Konov, E.M. Dianov, Mode-locked 1.93 m thulium fiber laser with a carbon nanotube absorber, Opt. Lett. 33 (2008) 1336–1338. [9] V. Scardaci, Z.Z. Sun, F. Wang, A.G. Rozhin, T. Hasan, F. Hennrich, I.H. White, W.I. Milne, A.C. Ferrari, Carbon nanotube polycarbonate composites for ultrafast lasers, Adv. Mater. 20 (2008) 4040–4043. [10] H. Kataura, Y. Kumazawa, Y. Maniwa, I. Umezu, S. Suzuki, Y. Ohtsuka, Y. Achiba, Optical properties of single-wall carbon nanotubes, Synth. Met. 103 (1999) 2555–2558. [11] M.S. Arnold, J.E. Sharping, S.I. Stupp, P. Kumar, M.C. Hersam, Band gap photobleaching in isolated single-walled carbon nanotubes, Nano Lett. 3 (2003) 1549–1554. [12] C.Y. Li, Y.G. Wang, K. Liu, C.Y. Tian, Q.J. Peng, Z.Y. Xu, LD end-pumped passively mode-locked Nd:YVO4 laser with single-walled carbon nanotubes, Laser Phys. 21 (2011) 2059–2063. [13] A. Schmidt, S. Rivier, W.B. Cho, J.H. Yim, S.Y. Choi, S. Lee, F. Rotermund, D. Rytz, G. Steinmeyer, V. Petrov, U. Griebner, Sub-100 fs single-walled carbon nanotube saturable absorber mode-locked Yb-laser operation near 1 m, Opt. Express 17 (2009) 20109–20116. [14] S. Liu, L. Jie, W. Guanggang, L. Li, S. Liu, M. Liu, W. Yonggang, Low-threshold diode-pumped CW passively mode-locked Nd:YVO4 laser, Optik 121 (2010) 19–22. [15] L. Sun, L. Zhang, H.J. Yu, L. Guo, J.L. Ma, J. Zhang, W. Hou, X.C. Lin, 880 nm LD pumped passive mode-locked TEM00 Nd:YVO4 laser based on SESAM, Laser Phys. Lett. 7 (2010) 711–714. [16] Y. Yan, Z.W. Fan, G. Niu, Y.T. Huang, J. Yu, 7 W laser diode end-pumped Nd:YVO4 passively mode-locking laser with a semiconductor saturable absorber mirror, Laser Phys. 22 (2012) 355–358. [17] Y. Liu, Y. Wang, J. Liu, C. Liu, High power ultrafast Nd:YVO4 laser mode locked by single wall carbon nanotube absorber, Appl. Phys. B 104 (2011) 835–838. [18] H.B. Qin, Y.G. Wang, H.B. Zhang, J. Liu, Z. Zhuo, A passively mode-locked Nd:YVO4 laser with a carbon nanotube saturable absorber, Laser Phys. 22 (2012) 684–687. [19] S.Y. Cheng, Y.G. Wang, J. Tang, L. Zhang, L. Sun, X.C. Lin, J.M. Li, Semiconductor type single wall carbon nanotube absorber for passive mode-locked Nd:YVO4 laser, Optik 123 (2012) 1279–1281. [20] C.Y. Li, Y. Bo, N. Zong, Y.G. Wang, B.X. Jiang, Y.B. Pan, G. Niu, Z.W. Fan, Q.J. Peng, D.F. Cui, Z.Y. Xu, LD-end-pumped passively Q-switched Nd:YAG ceramic laser with single wall carbon nanotube saturable absorber, Opt. Laser Technol. 44 (2012) 2149–2153.
Contents lists available at ScienceDirect
Optik journal homepage: www.elsevier.de/ijleo
Reflective carbon nanotube as the saturable absorber for mode-locked 1064 nm laser Mingwen Fan a , Baomin Ma b , Jie Liu a,∗ , Yonggang Wang c a
College of Physics and Electronics, Shandong Normal University, Jinan 250014, China School of Information Science and Engineering, Shandong University, Jinan 250100, China State Key Laboratory of Transient Optics and Photonics, Xi’an Institute of Optics and Precision Mechanics, Chinese Academy of Sciences, Xi’an 710119, China b c
a r t i c l e
i n f o
Article history: Received 22 October 2013 Accepted 27 May 2014 PACS: 42.55.Xi 42.60.Fc 42.65.Re 42.70.Nq
a b s t r a c t With a reflective single-walled carbon nanotube as the saturable absorber, a laser diode-pumped passively mode-locked Nd:YVO4 laser at 1064 nm was realized for the first time. The pulse duration of 12 ps was produced with a repetition rate of 83.7 MHz. The peak power and the single pulse energy of the mode-locking laser were 1.28 kW and 15.4 nJ, respectively. © 2014 Elsevier GmbH. All rights reserved.
Keywords: Reflective single walled carbon nanotube saturable absorber Mode-locked lasers Nd:YVO4 crystal
1. Introduction All-solid-state passively mode-locked lasers in the infrared spectra have wide applications in spectroscopy, optical communications, material processing, nonlinear frequency translation, medical treatments, etc. [1,2]. Development of new gain media and mode-locked devices has changed the outlook of ultrafast lasers over the past two decades. Particularly, the realization of different mode-locked devices has pushed the applications of ultrafast pulses to a realm broader than ever before. As a relatively traditional mode-locking technique, the semiconductor saturable absorber mirrors (SESAMs) were widely used in the past few years [3]. Nevertheless, current mode-locked technologies still suffer from drawbacks. The fabrication of SESAMs requires complicated deposition techniques and has disadvantages of relatively narrow operational range and long recovery times [4]. These limitations motivate research on new materials, novel designs and technologies [5]. Compared to SESAM, single walled
∗ Corresponding author. Tel.: +86 15264153867. E-mail address: [email protected] (J. Liu). http://dx.doi.org/10.1016/j.ijleo.2014.07.051 0030-4026/© 2014 Elsevier GmbH. All rights reserved.
carbon nanotube saturable absorber (SWCNT-SA) can be fabricated by simple and economy-costed methods, such as spray [6], spin coating [7] or horizontal evaporation methods [8,9]. Additionally, SWCNT-SA has excellent chemical stability, short recovery times and broad spectral range throughout the near-infrared ranges above 1.0 m, which was controlled by varying the tube diameter and its characteristic [10,11]. Recently, the SWCNT-SAs have been widely used for ultrashort pulse generation on the passively mode-locked solid-state lasers [12,13]. SWCNT-SAs can be fabricated as transmission-type and reflection-type. Generally, in comparison with the transmission-type, the reflection-type has less non-saturable loss. The laser gain medium Nd:YVO4 , due to its high absorption coefficient and large stimulated emission cross section, has been proved to be excellent laser material for achieving mode-locked lasers around 1 m [14]. Until now, there are a great number of researches on diode-pumped Nd:YVO4 lasers based on SESAM [15,16] and transmission SWCNT-SA [17–19]. However, there has never been reported on a diode-pumped passively mode-locked Nd:YVO4 laser by a reflective single walled carbon nanotube saturable absorber (RSWCNT-SA). In this paper, by using a RSWCNT-SA as the saturable absorber, a diode-pumped passively mode-locked Nd:YVO4 laser at
M. Fan et al. / Optik 125 (2014) 5666–5668
5667
Fig. 1. Schematic configuration of the W-type cavity.
1 m was realized for the first time. The laser operated at a repetition frequency of 83.7 MHz. A pulse duration of 12 ps was produced with a single pulse energy of 15.4 nJ for a RSWCNT-SA mode-locked laser, and its peak power reached to 1.28 kW.
Fig. 3. (a) Pulse train of the cw mode-locking laser recorded in 10 ns per division time scale. The inset figure (b) corresponds to the pulse train recorded in 1 s per division time scale.
3. Results and discussion 2. Experimental setup A schematic diagram of the experimental apparatus was shown in Fig. 1. The fiber-coupled diode laser was used as the pump source, which had a core-diameter of 400 m and a N.A. of 0.22. The emitting wavelength of the laser diode was 808 nm with the maximum available output power of 30 W. The pump laser was focused on the Nd:YVO4 crystal with a radius of 200 m by 1:1 focus lens. The dimension of Nd:YVO4 crystal with doping concentration of 0.5 at. % was 4 × 4 × 8 mm3 . In the experiment, the laser crystal was mounted in a Cu holder whose temperature was stabilized at 14 ◦ C by circulating water. Laser cavity consisted of three mirrors. The left side of the Nd:YVO4 crystal was coated to be highly reflecting at 1064 nm, and anti-reflecting (AR) at 808 nm pumping wavelength, which also acted as the input mirror. The other side of the crystal was coated for AR at 1064 nm and 808 nm. M1 and M2 were high-reflection coated at 1064 nm with radii of curvature of 200 mm and 800 mm, respectively. The RSWCNT-SA employed here was similar to that in [20], acted as a flat mirror and saturable absorber. We selected the transmission of 3% as the output coupler (OC) with radius of curvature of 200 mm. The length of the folded cavity was 1790 mm. The laser cavity was carefully designed to guarantee a sufficient small mode area in the gain medium and an appropriate operation of RSWCNT-SA in the strong saturation regime within its damage threshold. Using the ABCD-matrix method, we calculated the mode radius at the RSWCNT-SA to be 62 m.
Average output power / W
1.8
The relation of the mode-locked output power versus the absorbed pump power of the laser was shown in Fig. 2. From the drawing, we can see that the laser absorbed pump power threshold was about 0.38 W. Along with the increase of the pump power, Qswitched mode-locked (QML) laser was exhibited first. When the absorbed pump power was greater than 3.54 W, the laser exhibits stable continuous wave (cw) mode-locked operation. When the absorbed pump power was increased to 7.02 W, the average output power of cw mode-locked pulse was 1.78 W with the transverse mode remained as TEM00. It can be seen that the average output power increased linearly with the pump power. No pump saturation was observed, in order to protect the laser crystal from damage, we did not increase the pump power any more. Fig. 3 depicted the cw mode-locked pulse trains detected by a fast photodiode with a rising time of 400 ps (NEW FOCUS 1611) and recorded with a digital storage oscilloscope with 1 GHz bandwidth (Tektronix TDS 5104). Fig. 3(a) was recorded with a time scale of 10 ns/div, while Fig. 3(b) was recorded with a time scale of 1 s/div. It can be seen that the pulse trains are fully modulated with good pulse stability. The pulse repetition was 83.7 MHz, which was in agreement with the cavity length f = c/2L (c is the speed of light, L is the total length of the resonator). From Fig. 3(b), we can see that the pulse train is not plain. We thought the characteristic of the RSWCNT-SA leads to this phenomenon. Fig. 4 illustrated the measured autocorrelation trace corresponding to the absorbed pump power of 4.83 W in the cw mode-locked regime. The pulse width was 12 ps.
Linear Fitting
1.5 1.2 0.9
CWML
QML
0.6 0.3 0.0 0
1
2
3
4
5
6
7
8
Absorbed pump power / W Fig. 2. Variation of the average output power with the absorbed pump power.
Fig. 4. Autocorrelation trace of the pulse with the absorbed pump power of 4.83 W.
5668
M. Fan et al. / Optik 125 (2014) 5666–5668
projects of Shandong Province Science and Technology (Grant No. 2013GGX10108).
Intensity / a.u.
1.0 0.8
References
0.6
=1.6nm
0.4 0.2 0.0 1050
1055
1060
1065
1070
1075
1080
Wavelength / nm Fig. 5. The emission spectrum with the central wavelength of 1064 nm.
Optical spectrum of cw mode-locked laser measured with optical spectrum analyzer (AvaSpec-3648-USB2) was illustrated in Fig. 5. The full width at half maximum (FWHM) of cw mode-locked spectra was measured to be 1.6 nm. The central wavelength was 1064 nm. According to the average output power and pulse repetition rate, the maximum single pulse energy of 15.4 nJ and peak power of 1.28 kW were obtained under the absorbed pump power of 4.83 W. It corresponded to the time–bandwidth product of 5, which was larger than the transform-limited value of 0.314 for sech2 pulses, and indicated that the mode-locked pulses were frequency chirped and their duration could be further narrowed. When the folding angle between each mirror was relatively big, it will generate too many losses in the experiment with the result that we got a relatively wide pulse. The above factor leaded to the larger time–bandwidth product. Therefore, in my opinion, much shorter pulses can be obtained by optimizing the cavity. 4. Conclusions In conclusion, steady state mode-locked operation of a Nd:YVO4 laser is reported with using a RSWCNT-SA for the first time. 1.78 W average output power is obtained at an absorbed pump power of 7.02 W. The laser operates at a repetition frequency of 83.7 MHz with the central wavelength of 1064 nm. The highest pulse energy of 15.4 nJ for a RSWCNT-SA mode-locked laser is obtained, corresponding to its maximum peak power of 1.28 kW. Our experimental results show that the RSWCNT-SA is a promising saturable absorber for mode-locked laser. Acknowledgements This work has been supported by the National Natural Science Foundation of China (Grant No. 61078032) and development
[1] U. Keller, Recent developments in compact ultrafast lasers, Nature 424 (2003) 831–838. [2] U. Keller, Ultrafast solid-state laser oscillators: a success story for the last 20 years with no end in sight, Appl. Phys. B 100 (2010) 15–28. [3] U. Keller, K.J. Weingarten, F.X. Kärtner, D. Kopf, B. Braun, S.D. Jung, R. Fluck, C. Hönninger, N. Matuschek, J. Aus der Au, Semiconductor saturable absorber mirrors (SESAM’s) for femtosecond to nanosecond pulse generation in solid-state lasers, IEEE J. Sel. Top. Quantum Electron. 2 (1996) 435–453. [4] M. Haiml, R. Grange, U. Keller, Optical characterization of semiconductor saturable absorbers, Appl. Phys. B 79 (2004) 331–339. [5] Z. Sun, T. Hasan, A.C. Ferrari, Ultrafast lasers mode-locked by nanotubes and graphene, Phys. E 44 (2012) 1082–1091. [6] Y.W. Song, S. Yamashita, C.S. Goh, S.Y. Set, Passively mode-locked lasers with 17.2-GHz fundamental-mode repetition rate pulsed by carbon nanotubes, Opt. Lett. 32 (2007) 430–432. [7] J.H. Yim, W.B. Cho, S. Lee, Y.H. Ahn, K. Kim, H. Lim, G. Steinmeyer, V. Petrov, U. Griebner, F. Rotermund, Fabrication and characterization of ultrafast carbon nanotube saturable absorbers for solid-state laser mode locking near 1 m, Appl. Phys. Lett. 93 (2008) 161106–161108. [8] M.A. Solodyankin, E.D. Obraztsova, A.S. Lobach, A.I. Chernov, A.V. Tausenev, V.I. Konov, E.M. Dianov, Mode-locked 1.93 m thulium fiber laser with a carbon nanotube absorber, Opt. Lett. 33 (2008) 1336–1338. [9] V. Scardaci, Z.Z. Sun, F. Wang, A.G. Rozhin, T. Hasan, F. Hennrich, I.H. White, W.I. Milne, A.C. Ferrari, Carbon nanotube polycarbonate composites for ultrafast lasers, Adv. Mater. 20 (2008) 4040–4043. [10] H. Kataura, Y. Kumazawa, Y. Maniwa, I. Umezu, S. Suzuki, Y. Ohtsuka, Y. Achiba, Optical properties of single-wall carbon nanotubes, Synth. Met. 103 (1999) 2555–2558. [11] M.S. Arnold, J.E. Sharping, S.I. Stupp, P. Kumar, M.C. Hersam, Band gap photobleaching in isolated single-walled carbon nanotubes, Nano Lett. 3 (2003) 1549–1554. [12] C.Y. Li, Y.G. Wang, K. Liu, C.Y. Tian, Q.J. Peng, Z.Y. Xu, LD end-pumped passively mode-locked Nd:YVO4 laser with single-walled carbon nanotubes, Laser Phys. 21 (2011) 2059–2063. [13] A. Schmidt, S. Rivier, W.B. Cho, J.H. Yim, S.Y. Choi, S. Lee, F. Rotermund, D. Rytz, G. Steinmeyer, V. Petrov, U. Griebner, Sub-100 fs single-walled carbon nanotube saturable absorber mode-locked Yb-laser operation near 1 m, Opt. Express 17 (2009) 20109–20116. [14] S. Liu, L. Jie, W. Guanggang, L. Li, S. Liu, M. Liu, W. Yonggang, Low-threshold diode-pumped CW passively mode-locked Nd:YVO4 laser, Optik 121 (2010) 19–22. [15] L. Sun, L. Zhang, H.J. Yu, L. Guo, J.L. Ma, J. Zhang, W. Hou, X.C. Lin, 880 nm LD pumped passive mode-locked TEM00 Nd:YVO4 laser based on SESAM, Laser Phys. Lett. 7 (2010) 711–714. [16] Y. Yan, Z.W. Fan, G. Niu, Y.T. Huang, J. Yu, 7 W laser diode end-pumped Nd:YVO4 passively mode-locking laser with a semiconductor saturable absorber mirror, Laser Phys. 22 (2012) 355–358. [17] Y. Liu, Y. Wang, J. Liu, C. Liu, High power ultrafast Nd:YVO4 laser mode locked by single wall carbon nanotube absorber, Appl. Phys. B 104 (2011) 835–838. [18] H.B. Qin, Y.G. Wang, H.B. Zhang, J. Liu, Z. Zhuo, A passively mode-locked Nd:YVO4 laser with a carbon nanotube saturable absorber, Laser Phys. 22 (2012) 684–687. [19] S.Y. Cheng, Y.G. Wang, J. Tang, L. Zhang, L. Sun, X.C. Lin, J.M. Li, Semiconductor type single wall carbon nanotube absorber for passive mode-locked Nd:YVO4 laser, Optik 123 (2012) 1279–1281. [20] C.Y. Li, Y. Bo, N. Zong, Y.G. Wang, B.X. Jiang, Y.B. Pan, G. Niu, Z.W. Fan, Q.J. Peng, D.F. Cui, Z.Y. Xu, LD-end-pumped passively Q-switched Nd:YAG ceramic laser with single wall carbon nanotube saturable absorber, Opt. Laser Technol. 44 (2012) 2149–2153.