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OPTICS LETTERS / Vol. 39, No. 15 / August 1, 2014
Core-pumped femtosecond Nd:fiber laser at 910 and 935 nm Xiang Gao,1 Weijian Zong,1,2 Bingying Chen,1 Jian Zhang,1 Chen Li,1 Yizhou Liu,1 Aimin Wang,1,* Yanrong Song,3 and Zhigang Zhang1 1
State Key Laboratory of Advanced Optical Communication System and Networks School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China 2
Department of Cognitive Sciences, Institute of Basic Medical Sciences, Beijing 100850, China 3
School of Applied Science, Beijing University of Technology, Beijing 100124, China *Corresponding author: [email protected] Received April 14, 2014; revised June 23, 2014; accepted June 23, 2014; posted June 24, 2014 (Doc. ID 210108); published July 23, 2014
We report a core-pumped all-normal dispersion mode-locked Nd-doped fiber laser at 910 and 935 nm. The pulse is compressed to 198 fs, and the pulse energy is 1.3 nJ. The slope efficiency is more than 14%. This laser is tested as the optical source for the two-photon fluorescence imaging of pollen. © 2014 Optical Society of America OCIS codes: (320.7090) Ultrafast lasers; (140.3510) Lasers, fiber; (140.3530) Lasers, neodymium. http://dx.doi.org/10.1364/OL.39.004404
Two-photon fluorescence microscopy (TPFM) with 890– 950 nm femtosecond laser pulses is an important tool for deep tissue imaging and in vivo dynamic observation, since some fluorescing proteins, such as ECFP (enhanced cyan fluorescent protein) and EGFP (enhanced green fluorescent protein), demonstrate a relatively strong two-photon excitation at ∼900 nm [1,2]. The optical sources for this application have been dominated by mode-locked tunable Ti:sapphire lasers [3,4]. However, the Ti:sapphire lasers usually face problems in bulkiness, slow turn-key operation and high-cost maintenance, which bring inconvenience in application, especially in the compactness, portability, and miniaturization of TPFM systems. One alternative solution is the Nd:fiber laser. Nd-doped silica fiber has two typical emission peaks from 800 to 1100 nm: one is a three-level emission system (4 F3∕2 − 4 I9∕2 ) at ∼900 nm, and the other is a four-level one (4 F3∕2 − 4 I11∕2 ) at ∼1080 nm. To realize the Nd:fiber laser working at ∼900 nm, the main problem is that the radiation is severely overwhelmed by the four-level transition at ∼1080 nm because of its low lasing threshold and high efficiency at room temperature [5,6]. In previous studies, three possible solutions were demonstrated: (1) to take advantage of Nd-doped fiber with special doping concentration of Neodymium [7] or other elements, such as aluminum and germanium [8]; (2) to exploit a specially designed fiber structure, including photonic bandgap fiber [9] and W-type Nd-doped double cladding fiber as gain medium [10–12]; and (3) to cool down the Nddoped fiber in liquid nitrogen [13]. All of these schemes can help to suppress the emission at ∼1080 nm and thus enhance that at ∼900 nm. However, the laser [7] adopted active mode-locking and hence showed no self-starting feature. Core-pumped single clad fiber lasers with semiconductor saturable absorber mirrors (SESAMs) produced relatively low output power with low slope efficiency (1–2 mW output under 60–100 mW pump power in Refs. [14,15]), while those with cladding-pumped W-type Nd-doped fiber that can suppress ∼1080 nm transition and allow for a higher pump power showed extremely low slope efficiency (200 nm) ranged from 750 to 950 nm, the pulse energy of components at 890–950 nm was limited to several hundreds of picojoules, which could not meet the energy threshold of two-photon imaging systems with a strong amplification stage. In this Letter, we report a high-efficient core-pumped all-normal dispersion mode-locked Nd:fiber laser that can operate at 910 and 935 nm, with a repetition rate up to 46 MHz. The pulse energy reaches up to 1.3 nJ, with a slope efficiency up to 14%. To the best of our knowledge, this is the first highly efficient core-pumped mode-locked Nd:fiber laser in the all-normal dispersion regime at this wavelength region. The laser setup is shown in Fig. 1. Since the zero dispersion wavelength (∼1300 nm) of silica fiber is far beyond ∼900 nm, the laser runs at an all-normal dispersion regime. This usually allows for higher output power and pulse energy compared with other regimes that include dispersion compensation, though it requires
Fig. 1. Schematic of the laser setup. PBS, polarization beam splitter; HWP, half-wave plate; QWP, quarter-wave plate; WDM, wavelength-division multiplexer; FR, Faraday rotator; DM, short-pass dichroic mirror; and BRF, birefringent filter. © 2014 Optical Society of America
August 1, 2014 / Vol. 39, No. 15 / OPTICS LETTERS
a higher pumping threshold. The Nd-doped gain fiber is about 3.5 m long with the absorption of ∼8 dB∕m at 810 nm. The core composition is Ge-doped silica with Nd3 ion concentration of 500–1000 ppm [9]. The rest fiber in the cavity is a single mode silica fiber with cutoff wavelength at ∼730 nm and core diameter of 4.4 μm. The total fiber length in the cavity is 4.2 m, with the free-space distance less than 20 cm. The two PBSs and the Faraday rotator and half-wave plate between them serve as an intracavity isolator, which is helpful for self-start modelocking. A birefringent filter is also employed in the free-space region for spectrum filtering in all-normal dispersion regime and tuning as well. Slightly oblique when crossing the incident beam, when tuning the birefringent filter by angle, it has a tunable bandwidth from 0 to 8 THz around 920 nm, which corresponds to 0 to 22 nm. To suppress the strong laser oscillation at ∼1080 nm, a short-pass dichroic mirror with a high transmission at ∼900 nm and high reflectivity at ∼1080 nm is inserted into the cavity. All other optical components are designed for the high transmission at the central wavelength of 920 nm. Since the group velocity dispersion (GVD) of the gain fiber and single mode fiber is estimated to be 27.8 fs2 ∕mm, the net dispersion of the cavity is around 1.18 × 105 fs2 . The pump laser is a single mode fiber-coupled 808 nm laser diode that delivers up to 250 mW. To meet the relatively high energy threshold for mode-locking, two pump lasers with the total power of >400 mW are coupled from both sides of the gain fiber through two wavelength division multiplexers (WDMs) into the cavity. The mode-locking mechanism is based on nonlinear polarization evolution (NPE), which has been exploited in [12]. To verify the feasibility of mode-locking at 910 nm, we simulated pulse evolution in the laser cavity. Figure 2(a) shows the evolution of the intracavity spectral bandwidth and pulse duration, and Fig. 2(b) shows the evolution of the intracavity spectral profile. In the simulation, we inserted a bandpass filter and set the bandwidth as ∼10 nm around 910 nm. The simulation concluded that with this filter, we could obtain a stable dissipative solution. The average output power can be as high as 60 mW under the pump power of 420 mW. The slope efficiency is about 14%. The continuous wave laser can be easily realized with the central wavelength at 910 nm. By adjusting the wave plates and the birefringent filter, the laser can be easily mode-locked. Meanwhile, the mode-locking shows an excellent feature of self-starting. The laser output power at 910 nm as a function of the pump power is depicted in Fig. 3. Because of the huge insertion loss of the customized isolators at 808 nm for pumps, the maximum pump power is 420 mW before aligning the 808 nm light into the cavity via WDMs. Under this pump power, the CW output is 71 mW. When modelocked, the output power drops slightly to 60 mW. Modelocked pulses at 935 nm with 47 mW output power can also be acquired simply by turning the birefringent filter. The repetition rate is measured to be 46 MHz. The corresponding pulse energies are 1.3 nJ at 910 nm and 1 nJ at 935 nm. The small discrepancy between the pulse energies at these two mode-locking wavelengths can be
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Fig. 2. (a) Evolution of pulse duration (black dots) and spectral bandwidth (red dots) at 910 nm. SMF1 and SMF2, single-mode fiber; BF, free space part including bandpass filter, saturable absorber, and laser output. (b) Simulated optical spectra from different positions inside the cavity.
attributed to the gain profile of the Nd-doped fiber and the bandpass losses of optical elements in the cavity. Figure 4(a) shows the spectra of the mode-locked pulses for the central wavelength of 910 and 935 nm respectively. The spectra exhibit a typical feature of allnormal dispersion mode-locking. The bandwidths of pulse spectra are 11 nm at 910 nm and 10 nm at 935 nm. Figure 4(b) shows the pulse spectrum in log
Fig. 3. Laser output power on the pump power at 910 nm.
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Fig. 4. (a) Linear spectra of mode-locked pulses at 910 and 935 nm and (b) pulse spectrum at 910 nm in log scale.
scale. Because of the short-pass dichroic mirror, the photons above 1 μm are reflected out of the cavity and cannot form oscillation. Therefore, in Fig. 4(b), the spectrum above 1 μm only shows spontaneous emission. The contrast between the mode-locking at 910 nm and spontaneous emission above 1 μm is 33 dB. The output pulse is positively chirped and is dechirped by a pair of gratings. The calculated and measured intensity autocorrelation traces are superimposed in Fig. 5. Under the assumption of the Gaussian profile, the pulse durations are estimated to be 198 and 264 fs for 910 and 935 nm respectively, close to the calculated Fourier transform limited pulses of 190 and 250 fs. The time– bandwidth products at these two wavelengths are 0.78 and 0.90, which are near to the calculated results of 0.76 and 0.86. Because of the insertion loss of the grating pair and reflective mirrors, the output power reduces to 38 mW after pulse compression. To prove the imaging potential of the laser in TPFM, we conducted a test in our homemade two-photon microscopic system. The specimen, pollen, has intrinsic florescence emission under two-photon excitation. Before
Fig. 6. Imaging of pollen using self-made TPFM system (speed, 4 fps; objective, 20×, N.A. 0.8) and the femtosecond fiber laser at 910 nm.
entering the microscope, the 910 nm pulse was amplified up to 114 mW in a core-pumped fiber amplification stage and passed through a grating pair compressor. The pulse width was 217 fs, with energy of 1.5 nJ and average power of 71 mW at the entrance of the microscope. The average power after the objective lens was 17 mW. The two-photon fluorescence imaging of pollen is shown in Fig. 6. It clearly shows details of the pollen with the resolution of a micrometer scale. In conclusion, we have demonstrated for the first time to the best of our knowledge an efficient femtosecond pulse generation in a core-pumped mode-locked fiber laser at 910 and 935 nm in the all-normal dispersion regime. The laser produces an output power of 60 mW at 910 nm and 47 mW at 935 nm under the pump power of 420 mW, corresponding to pulse energies of 1.3 and 1 nJ respectively. The slope efficiency is up to 14%. The pulse widths for those two central wavelengths are 198 and 264 fs respectively. We also performed a TPFM imaging test for the laser that proved the resolution of the imaging. This laser can be an ideal light source to replace the expensive Ti:sapphire lasers for miniaturized portable TPFM systems. This work was partially supported by the National Natural Science Foundation of China (Grant Nos. 61177047 and 31327901). We acknowledge Prof. Heping Cheng, Prof. Liangyi Chen, and Prof. Zhuan Zhou from Institute of Molecular Medicine, Peking University for their help in the laser and TPFM imaging experiments.
Fig. 5. (a) Calculated intensity autocorrelation traces of the pulses for 910 nm (black) and 935 nm (red). (b) Measured intensity autocorrelation traces for 910 nm (black) and 935 nm (red).
References 1. M. Drobizhev, N. S. Makarov, S. E. Tillo, T. E. Hughes, and A. Rebane, Nat. Methods 8, 393 (2011). 2. J. Herz, V. Siffrin, A. E. Hauser, A. U. Brandt, T. Leuenberger, H. Radbruch, F. Zipp, and R. A. Niesner, Biophys. J. 98, 715 (2010). 3. F. Helmchen and W. Denk, Nat. Methods 2, 932 (2005).
August 1, 2014 / Vol. 39, No. 15 / OPTICS LETTERS 4. G. J. Brakenhoff, J. Squier, T. Norris, A. C. Bliton, M. H. Wade, and B. Athey, J. Microsc. 181, 253 (1996). 5. K. Arai, H. Namikawa, K. Kumata, T. Honda, Y. Ishii, and T. Handa, J. Appl. Phys. 59, 3430 (1986). 6. B. J. Ainslie, S. P. Craig, and S. T. Davey, Mater. Lett. 5, 143 (1987). 7. R. Hofer, M. Hofer, G. A. Reider, M. Cernusca, and M. H. Ober, Opt. Commun. 140, 242 (1997). 8. A. Cook and H. Hendricks, Appl. Opt. 37, 3276 (1998). 9. A. Wang, A. K. George, and J. C. Knight, Opt. Lett. 31, 1388 (2006). 10. D. B. S. Soh, Y. Seongwoo, J. Nilsson, J. K. Sahu, K. Oh, S. Baek, Y. Jeong, C. Codemard, P. Dupriez, J. Kim, and V. Philippov, IEEE J. Quantum Electron. 40, 1275 (2004). 11. S. Yoo, D. B. S. Soh, J. Kim, Y. Jung, J. Nilsson, J. K. Sahu, J. W. Lee, and K. Oh, Opt. Commun. 247, 153 (2005).
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12. K. Qian, H. Wang, M. Laroche, and A. Hideur, Opt. Lett. 39, 267 (2014). 13. J. W. Dawson, A. Drobshoff, Z. M. Liao, R. J. Beach, D. M. Pennington, S. A. Payne, L. Taylor, W. K. P. Hackenberg, and D. Bonaccini, Proc. SPIE 4974, 75 (2003). 14. M. Rusu, S. Karirinne, M. Guina, A. B. Grudinin, and O. G. Okhotnikov, IEEE Photon. Technol. Lett. 16, 1029 (2004). 15. M. D. Guina, M. Rusu, S. Karirinne, O. G. Okhotnikov, and A. B. Grudinin, in Conference on Lasers and Electro-Optics/ International Quantum Electronics Conference and Photonic Applications Systems Technologies, OSA Technical Digest (CD) (Optical Society of America, 2004), paper CMAA3. 16. H. Chen, Z. Haider, J. Lim, S. Xu, Z. Yang, F. Kärtner, and G. Chang, Opt. Lett. 38, 4927 (2013).
OPTICS LETTERS / Vol. 39, No. 15 / August 1, 2014
Core-pumped femtosecond Nd:fiber laser at 910 and 935 nm Xiang Gao,1 Weijian Zong,1,2 Bingying Chen,1 Jian Zhang,1 Chen Li,1 Yizhou Liu,1 Aimin Wang,1,* Yanrong Song,3 and Zhigang Zhang1 1
State Key Laboratory of Advanced Optical Communication System and Networks School of Electronics Engineering and Computer Science, Peking University, Beijing 100871, China 2
Department of Cognitive Sciences, Institute of Basic Medical Sciences, Beijing 100850, China 3
School of Applied Science, Beijing University of Technology, Beijing 100124, China *Corresponding author: [email protected] Received April 14, 2014; revised June 23, 2014; accepted June 23, 2014; posted June 24, 2014 (Doc. ID 210108); published July 23, 2014
We report a core-pumped all-normal dispersion mode-locked Nd-doped fiber laser at 910 and 935 nm. The pulse is compressed to 198 fs, and the pulse energy is 1.3 nJ. The slope efficiency is more than 14%. This laser is tested as the optical source for the two-photon fluorescence imaging of pollen. © 2014 Optical Society of America OCIS codes: (320.7090) Ultrafast lasers; (140.3510) Lasers, fiber; (140.3530) Lasers, neodymium. http://dx.doi.org/10.1364/OL.39.004404
Two-photon fluorescence microscopy (TPFM) with 890– 950 nm femtosecond laser pulses is an important tool for deep tissue imaging and in vivo dynamic observation, since some fluorescing proteins, such as ECFP (enhanced cyan fluorescent protein) and EGFP (enhanced green fluorescent protein), demonstrate a relatively strong two-photon excitation at ∼900 nm [1,2]. The optical sources for this application have been dominated by mode-locked tunable Ti:sapphire lasers [3,4]. However, the Ti:sapphire lasers usually face problems in bulkiness, slow turn-key operation and high-cost maintenance, which bring inconvenience in application, especially in the compactness, portability, and miniaturization of TPFM systems. One alternative solution is the Nd:fiber laser. Nd-doped silica fiber has two typical emission peaks from 800 to 1100 nm: one is a three-level emission system (4 F3∕2 − 4 I9∕2 ) at ∼900 nm, and the other is a four-level one (4 F3∕2 − 4 I11∕2 ) at ∼1080 nm. To realize the Nd:fiber laser working at ∼900 nm, the main problem is that the radiation is severely overwhelmed by the four-level transition at ∼1080 nm because of its low lasing threshold and high efficiency at room temperature [5,6]. In previous studies, three possible solutions were demonstrated: (1) to take advantage of Nd-doped fiber with special doping concentration of Neodymium [7] or other elements, such as aluminum and germanium [8]; (2) to exploit a specially designed fiber structure, including photonic bandgap fiber [9] and W-type Nd-doped double cladding fiber as gain medium [10–12]; and (3) to cool down the Nddoped fiber in liquid nitrogen [13]. All of these schemes can help to suppress the emission at ∼1080 nm and thus enhance that at ∼900 nm. However, the laser [7] adopted active mode-locking and hence showed no self-starting feature. Core-pumped single clad fiber lasers with semiconductor saturable absorber mirrors (SESAMs) produced relatively low output power with low slope efficiency (1–2 mW output under 60–100 mW pump power in Refs. [14,15]), while those with cladding-pumped W-type Nd-doped fiber that can suppress ∼1080 nm transition and allow for a higher pump power showed extremely low slope efficiency (200 nm) ranged from 750 to 950 nm, the pulse energy of components at 890–950 nm was limited to several hundreds of picojoules, which could not meet the energy threshold of two-photon imaging systems with a strong amplification stage. In this Letter, we report a high-efficient core-pumped all-normal dispersion mode-locked Nd:fiber laser that can operate at 910 and 935 nm, with a repetition rate up to 46 MHz. The pulse energy reaches up to 1.3 nJ, with a slope efficiency up to 14%. To the best of our knowledge, this is the first highly efficient core-pumped mode-locked Nd:fiber laser in the all-normal dispersion regime at this wavelength region. The laser setup is shown in Fig. 1. Since the zero dispersion wavelength (∼1300 nm) of silica fiber is far beyond ∼900 nm, the laser runs at an all-normal dispersion regime. This usually allows for higher output power and pulse energy compared with other regimes that include dispersion compensation, though it requires
Fig. 1. Schematic of the laser setup. PBS, polarization beam splitter; HWP, half-wave plate; QWP, quarter-wave plate; WDM, wavelength-division multiplexer; FR, Faraday rotator; DM, short-pass dichroic mirror; and BRF, birefringent filter. © 2014 Optical Society of America
August 1, 2014 / Vol. 39, No. 15 / OPTICS LETTERS
a higher pumping threshold. The Nd-doped gain fiber is about 3.5 m long with the absorption of ∼8 dB∕m at 810 nm. The core composition is Ge-doped silica with Nd3 ion concentration of 500–1000 ppm [9]. The rest fiber in the cavity is a single mode silica fiber with cutoff wavelength at ∼730 nm and core diameter of 4.4 μm. The total fiber length in the cavity is 4.2 m, with the free-space distance less than 20 cm. The two PBSs and the Faraday rotator and half-wave plate between them serve as an intracavity isolator, which is helpful for self-start modelocking. A birefringent filter is also employed in the free-space region for spectrum filtering in all-normal dispersion regime and tuning as well. Slightly oblique when crossing the incident beam, when tuning the birefringent filter by angle, it has a tunable bandwidth from 0 to 8 THz around 920 nm, which corresponds to 0 to 22 nm. To suppress the strong laser oscillation at ∼1080 nm, a short-pass dichroic mirror with a high transmission at ∼900 nm and high reflectivity at ∼1080 nm is inserted into the cavity. All other optical components are designed for the high transmission at the central wavelength of 920 nm. Since the group velocity dispersion (GVD) of the gain fiber and single mode fiber is estimated to be 27.8 fs2 ∕mm, the net dispersion of the cavity is around 1.18 × 105 fs2 . The pump laser is a single mode fiber-coupled 808 nm laser diode that delivers up to 250 mW. To meet the relatively high energy threshold for mode-locking, two pump lasers with the total power of >400 mW are coupled from both sides of the gain fiber through two wavelength division multiplexers (WDMs) into the cavity. The mode-locking mechanism is based on nonlinear polarization evolution (NPE), which has been exploited in [12]. To verify the feasibility of mode-locking at 910 nm, we simulated pulse evolution in the laser cavity. Figure 2(a) shows the evolution of the intracavity spectral bandwidth and pulse duration, and Fig. 2(b) shows the evolution of the intracavity spectral profile. In the simulation, we inserted a bandpass filter and set the bandwidth as ∼10 nm around 910 nm. The simulation concluded that with this filter, we could obtain a stable dissipative solution. The average output power can be as high as 60 mW under the pump power of 420 mW. The slope efficiency is about 14%. The continuous wave laser can be easily realized with the central wavelength at 910 nm. By adjusting the wave plates and the birefringent filter, the laser can be easily mode-locked. Meanwhile, the mode-locking shows an excellent feature of self-starting. The laser output power at 910 nm as a function of the pump power is depicted in Fig. 3. Because of the huge insertion loss of the customized isolators at 808 nm for pumps, the maximum pump power is 420 mW before aligning the 808 nm light into the cavity via WDMs. Under this pump power, the CW output is 71 mW. When modelocked, the output power drops slightly to 60 mW. Modelocked pulses at 935 nm with 47 mW output power can also be acquired simply by turning the birefringent filter. The repetition rate is measured to be 46 MHz. The corresponding pulse energies are 1.3 nJ at 910 nm and 1 nJ at 935 nm. The small discrepancy between the pulse energies at these two mode-locking wavelengths can be
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Fig. 2. (a) Evolution of pulse duration (black dots) and spectral bandwidth (red dots) at 910 nm. SMF1 and SMF2, single-mode fiber; BF, free space part including bandpass filter, saturable absorber, and laser output. (b) Simulated optical spectra from different positions inside the cavity.
attributed to the gain profile of the Nd-doped fiber and the bandpass losses of optical elements in the cavity. Figure 4(a) shows the spectra of the mode-locked pulses for the central wavelength of 910 and 935 nm respectively. The spectra exhibit a typical feature of allnormal dispersion mode-locking. The bandwidths of pulse spectra are 11 nm at 910 nm and 10 nm at 935 nm. Figure 4(b) shows the pulse spectrum in log
Fig. 3. Laser output power on the pump power at 910 nm.
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Fig. 4. (a) Linear spectra of mode-locked pulses at 910 and 935 nm and (b) pulse spectrum at 910 nm in log scale.
scale. Because of the short-pass dichroic mirror, the photons above 1 μm are reflected out of the cavity and cannot form oscillation. Therefore, in Fig. 4(b), the spectrum above 1 μm only shows spontaneous emission. The contrast between the mode-locking at 910 nm and spontaneous emission above 1 μm is 33 dB. The output pulse is positively chirped and is dechirped by a pair of gratings. The calculated and measured intensity autocorrelation traces are superimposed in Fig. 5. Under the assumption of the Gaussian profile, the pulse durations are estimated to be 198 and 264 fs for 910 and 935 nm respectively, close to the calculated Fourier transform limited pulses of 190 and 250 fs. The time– bandwidth products at these two wavelengths are 0.78 and 0.90, which are near to the calculated results of 0.76 and 0.86. Because of the insertion loss of the grating pair and reflective mirrors, the output power reduces to 38 mW after pulse compression. To prove the imaging potential of the laser in TPFM, we conducted a test in our homemade two-photon microscopic system. The specimen, pollen, has intrinsic florescence emission under two-photon excitation. Before
Fig. 6. Imaging of pollen using self-made TPFM system (speed, 4 fps; objective, 20×, N.A. 0.8) and the femtosecond fiber laser at 910 nm.
entering the microscope, the 910 nm pulse was amplified up to 114 mW in a core-pumped fiber amplification stage and passed through a grating pair compressor. The pulse width was 217 fs, with energy of 1.5 nJ and average power of 71 mW at the entrance of the microscope. The average power after the objective lens was 17 mW. The two-photon fluorescence imaging of pollen is shown in Fig. 6. It clearly shows details of the pollen with the resolution of a micrometer scale. In conclusion, we have demonstrated for the first time to the best of our knowledge an efficient femtosecond pulse generation in a core-pumped mode-locked fiber laser at 910 and 935 nm in the all-normal dispersion regime. The laser produces an output power of 60 mW at 910 nm and 47 mW at 935 nm under the pump power of 420 mW, corresponding to pulse energies of 1.3 and 1 nJ respectively. The slope efficiency is up to 14%. The pulse widths for those two central wavelengths are 198 and 264 fs respectively. We also performed a TPFM imaging test for the laser that proved the resolution of the imaging. This laser can be an ideal light source to replace the expensive Ti:sapphire lasers for miniaturized portable TPFM systems. This work was partially supported by the National Natural Science Foundation of China (Grant Nos. 61177047 and 31327901). We acknowledge Prof. Heping Cheng, Prof. Liangyi Chen, and Prof. Zhuan Zhou from Institute of Molecular Medicine, Peking University for their help in the laser and TPFM imaging experiments.
Fig. 5. (a) Calculated intensity autocorrelation traces of the pulses for 910 nm (black) and 935 nm (red). (b) Measured intensity autocorrelation traces for 910 nm (black) and 935 nm (red).
References 1. M. Drobizhev, N. S. Makarov, S. E. Tillo, T. E. Hughes, and A. Rebane, Nat. Methods 8, 393 (2011). 2. J. Herz, V. Siffrin, A. E. Hauser, A. U. Brandt, T. Leuenberger, H. Radbruch, F. Zipp, and R. A. Niesner, Biophys. J. 98, 715 (2010). 3. F. Helmchen and W. Denk, Nat. Methods 2, 932 (2005).
August 1, 2014 / Vol. 39, No. 15 / OPTICS LETTERS 4. G. J. Brakenhoff, J. Squier, T. Norris, A. C. Bliton, M. H. Wade, and B. Athey, J. Microsc. 181, 253 (1996). 5. K. Arai, H. Namikawa, K. Kumata, T. Honda, Y. Ishii, and T. Handa, J. Appl. Phys. 59, 3430 (1986). 6. B. J. Ainslie, S. P. Craig, and S. T. Davey, Mater. Lett. 5, 143 (1987). 7. R. Hofer, M. Hofer, G. A. Reider, M. Cernusca, and M. H. Ober, Opt. Commun. 140, 242 (1997). 8. A. Cook and H. Hendricks, Appl. Opt. 37, 3276 (1998). 9. A. Wang, A. K. George, and J. C. Knight, Opt. Lett. 31, 1388 (2006). 10. D. B. S. Soh, Y. Seongwoo, J. Nilsson, J. K. Sahu, K. Oh, S. Baek, Y. Jeong, C. Codemard, P. Dupriez, J. Kim, and V. Philippov, IEEE J. Quantum Electron. 40, 1275 (2004). 11. S. Yoo, D. B. S. Soh, J. Kim, Y. Jung, J. Nilsson, J. K. Sahu, J. W. Lee, and K. Oh, Opt. Commun. 247, 153 (2005).
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12. K. Qian, H. Wang, M. Laroche, and A. Hideur, Opt. Lett. 39, 267 (2014). 13. J. W. Dawson, A. Drobshoff, Z. M. Liao, R. J. Beach, D. M. Pennington, S. A. Payne, L. Taylor, W. K. P. Hackenberg, and D. Bonaccini, Proc. SPIE 4974, 75 (2003). 14. M. Rusu, S. Karirinne, M. Guina, A. B. Grudinin, and O. G. Okhotnikov, IEEE Photon. Technol. Lett. 16, 1029 (2004). 15. M. D. Guina, M. Rusu, S. Karirinne, O. G. Okhotnikov, and A. B. Grudinin, in Conference on Lasers and Electro-Optics/ International Quantum Electronics Conference and Photonic Applications Systems Technologies, OSA Technical Digest (CD) (Optical Society of America, 2004), paper CMAA3. 16. H. Chen, Z. Haider, J. Lim, S. Xu, Z. Yang, F. Kärtner, and G. Chang, Opt. Lett. 38, 4927 (2013).
