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Virtual Journal for Biomedical Optics

| EXPLORING THE INTERFACE OF LIGHT AND BIOMEDICINE

  • Editors: Andrew Dunn and Anthony Durkin
  • Vol. 9, Iss. 5 — Apr. 29, 2014
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7-ps optical pulse generation from a 1064-nm gain-switched laser diode and its application for two-photon microscopy

Yuta Kusama, Yuichiro Tanushi, Masami Yokoyama, Ryosuke Kawakami, Terumasa Hibi, Yuichi Kozawa, Tomomi Nemoto, Shunichi Sato, and Hiroyuki Yokoyama  »View Author Affiliations


Optics Express, Vol. 22, Issue 5, pp. 5746-5753 (2014)
http://dx.doi.org/10.1364/OE.22.005746


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Abstract

In this study, we investigated the picosecond optical pulse generation from a 1064-nm distributed feedback laser diode under strong gain switching. The spectrum of the generated optical pulses was manipulated in two different ways: (i) by extracting the short-wavelength components of the optical pulse spectrum and (ii) by compensating for spectral chirping in the extracted mid-spectral region. Both of these methods shortened the optical pulse duration to approximately 7 ps. These optical pulses were amplified to over 20-kW peak power for two-photon microscopy. We obtained clear two-photon images of neurons in a fixed brain slice of H-line mouse expressing enhanced yellow fluorescent protein. Furthermore, a successful experiment was also confirmed for in vivo deep region H-line mouse brain neuron imaging.

© 2014 Optical Society of America

1. Introduction

Two-photon microscopy (TPM) of biological tissues expressing fluorescent proteins has been studied extensively, because TPM can be used to obtain three-dimensional (3-D) images with sub-micrometer spatial resolution. In general, TPM uses femtosecond optical pulses [1

1. W. Denk, J. H. Strickler, and W. W. Webb, “Two-photon laser scanning fluorescence microscopy,” Science 248(4951), 73–76 (1990). [CrossRef] [PubMed]

3

3. E. Spiess, F. Bestvater, A. Heckel-Pompey, K. Toth, M. Hacker, G. Stobrawa, T. Feurer, C. Wotzlaw, U. Berchner-Pfannschmidt, T. Porwol, and H. Acker, “Two-photon excitation and emission spectra of the green fluorescent protein variants ECFP, EGFP and EYFP,” J. Microsc. 217(3), 200–204 (2005). [CrossRef] [PubMed]

]; however, by simple consideration of the principle of two-photon absorption and subsequent fluorescence processes, picosecond pulses should have the same capability as femtosecond pulses when the peak power and average power are the same. We have successfully imaged biological specimens, using picosecond optical pulse sources, based on semiconductor laser diodes (LDs) [4

4. H. Yokoyama, H.-C. Guo, T. Yoda, K. Takashima, K. Sato, H. Taniguchi, and H. Ito, “Two-photon bioimaging with picosecond optical pulses from a semiconductor laser,” Opt. Express 14(8), 3467–3471 (2006). [CrossRef] [PubMed]

6

6. H. Yokoyama, A. Sato, H.-C. Guo, K. Sato, M. Mure, and H. Tsubokawa, “Nonlinear-microscopy optical-pulse sources based on mode-locked semiconductor lasers,” Opt. Express 16(22), 17752–17758 (2008). [CrossRef] [PubMed]

]. An advantage of this approach is that the picosecond pulses do not suffer from temporal broadening caused by dispersion in the optical components.

Compact, stable, ultrashort optical pulse sources, having a wavelength of ~1 μm, can be used to excite dominant fluorescent proteins present in biological specimens through a two-photon absorption process [2

2. P. F. Curley, A. I. Ferguson, J. G. White, and W. B. Amos, “Application of a femtosecond self-sustained mode-locked Ti:sapphire laser to the field of laser scanning confocal microscopy,” Opt. Quantum Electron. 24(8), 851–859 (1992). [CrossRef]

]. Additionally, light at this wavelength is not absorbed by water, oxyhemoglobin, deoxyhemoglobin, or melanin in the tissue [7

7. K. Plaetzer, B. Krammer, J. Berlanda, F. Berr, and T. Kiesslich, “Photophysics and photochemistry of photodynamic therapy: fundamental aspects,” Lasers Med. Sci. 24(2), 259–268 (2009). [CrossRef] [PubMed]

]. We have developed 1-μm-band picosecond pulse sources, based on mode-locked LDs (MLLDs) using InGaAs quantum-well (QW) laser diodes, and have demonstrated their effectiveness in deep-site TPM of biological tissue [6

6. H. Yokoyama, A. Sato, H.-C. Guo, K. Sato, M. Mure, and H. Tsubokawa, “Nonlinear-microscopy optical-pulse sources based on mode-locked semiconductor lasers,” Opt. Express 16(22), 17752–17758 (2008). [CrossRef] [PubMed]

,8

8. R. Kawakami, K. Sawada, A. Sato, T. Hibi, Y. Kozawa, S. Sato, H. Yokoyama, and T. Nemoto, “Visualizing hippocampal neurons with in vivo two-photon microscopy using a 1030 nm picoseconds pulse laser,” Sci. Reports 3, 1014 (2013).

]. MLLDs offer several advantages: optical pulses below several picoseconds in duration can be generated easily, due to the saturable absorber section incorporated into the LD device, and the synchronization of multiple MLLDs is possible using sinusoidal current modulation [6

6. H. Yokoyama, A. Sato, H.-C. Guo, K. Sato, M. Mure, and H. Tsubokawa, “Nonlinear-microscopy optical-pulse sources based on mode-locked semiconductor lasers,” Opt. Express 16(22), 17752–17758 (2008). [CrossRef] [PubMed]

]. However, the precise balance control of gain and saturable absorption is required for stable operation of an MLLD. Additionally, the MLLD cavity should be sufficiently short to ensure long-term stability; thus, the pulse repetition is set to frequencies in the gigahertz to sub-gigahertz range. An optical gating device can also be incorporated to control the optical pulse repetition rate [6

6. H. Yokoyama, A. Sato, H.-C. Guo, K. Sato, M. Mure, and H. Tsubokawa, “Nonlinear-microscopy optical-pulse sources based on mode-locked semiconductor lasers,” Opt. Express 16(22), 17752–17758 (2008). [CrossRef] [PubMed]

]. For TPM applications, the pulse repetition is generally from tens to one hundred megahertz to simultaneously satisfy the high peak power and low average power requirements.

Gain-switched LDs (GSLDs) [9

9. C. L. Lin, P. L. Liu, T. C. Damen, D. J. Eilenberger, and R. L. Hartman, “Simple picosecond pulse generation scheme for injection lasers,” Electron. Lett. 16(15), 600–601 (1980). [CrossRef]

] could potentially be ideal optical pulse sources for TPM, due to their reliability, ease of use, and long-time stability in the optical power and the laser oscillation mode. Moreover, in principle, the GSLDs can generate the optical pulses at flexible pulse repetition rates from single shot to over a gigahertz frequency. However, the temporal width of optical pulses generated from a GSLD is usually in the range of a few tens to several tens of picoseconds; these pulse durations are too long for TPM applications. It is noted, however, that the potential limit of ultrashort optical pulse generation from GSLDs is still not clear, because the detailed physical processes involved in the gain switching (GS) operation of a semiconductor laser have yet to be fully understood. We recently revealed that sub-5-ps optical pulses could be obtained by simply extracting the short-wavelength edge components of the optical output from a gain-switched 1.55-μm distributed feedback LD (DFB-LD), having a 20-GHz modulation frequency [4

4. H. Yokoyama, H.-C. Guo, T. Yoda, K. Takashima, K. Sato, H. Taniguchi, and H. Ito, “Two-photon bioimaging with picosecond optical pulses from a semiconductor laser,” Opt. Express 14(8), 3467–3471 (2006). [CrossRef] [PubMed]

,5

5. H. Yokoyama, H. Tsubokawa, H.-C. Guo, J. Shikata, K. Sato, K. Takashima, K. Kashiwagi, N. Saito, H. Taniguchi, and H. Ito, “Two-photon bioimaging utilizing supercontinuum light generated by a high-peak-power picosecond semiconductor laser source,” J. Biomed. Opt. 12(5), 054019 (2007). [CrossRef] [PubMed]

].

An important condition for generating shorter optical pulses from a GSLD is to create a very high carrier density inside the LD active layer via an intense transient excitation. Under this excitation, the optical output spectrum is broadened to cover almost the entire optical gain bandwidth for a cleaved facet LD (having a Fabry–Perot cavity). We have confirmed that a shorter wavelength component shows shorter temporal duration and earlier oscillation [10

10. H. Yokoyama, “Dynamics in gain-switched semiconductor lasers generating ultrashort optical pulses,” presented at OPTIC 2012, National Taiwan University, Taiwan, 6–8 Dec. (2012).

]; the initial lasing process occurred preferentially in the higher photon-energy region. In contrast, for a DFB-LD, which shows single-mode operation even under strong GS, the spectrum shows very different dynamic behaviors. A remarkable short wavelength shift occurs at the beginning of the GS laser oscillation; this is due to the refractive index decrease by carrier plasma effects under high-density carrier excitation [11

11. S. Q. Chen, A. Sato, T. Ito, M. Yoshita, H. Akiyama, and H. Yokoyama, “Sub-5-ps optical pulse generation from a 1.55-µm distributed-feedback laser diode with nanosecond electric pulse excitation and spectral filtering,” Opt. Express 20(22), 24843–24849 (2012). [CrossRef] [PubMed]

,12

12. S. Q. Chen, M. Yoshita, A. Sato, T. Ito, H. Akiyama, and H. Yokoyama, “Dynamics of short-pulse generation via spectral filtering from intensely excited gain-switched 1.55-μm distributed-feedback laser diodes,” Opt. Express 21(9), 10597–10605 (2013). [CrossRef] [PubMed]

]. Once the laser oscillation is initiated, the oscillation resonance wavelength shifts to the longer wavelength side, corresponding to a rapid carrier density decrease during GS-pulse generation. Under the conditions described above, Fourier-transform-limited (FTL) sub-5-ps optical pulses were obtained for a 1.55-μm DFB-LD by extracting the short-wavelength spectral components using an optical band pass filter (BPF) [11

11. S. Q. Chen, A. Sato, T. Ito, M. Yoshita, H. Akiyama, and H. Yokoyama, “Sub-5-ps optical pulse generation from a 1.55-µm distributed-feedback laser diode with nanosecond electric pulse excitation and spectral filtering,” Opt. Express 20(22), 24843–24849 (2012). [CrossRef] [PubMed]

,12

12. S. Q. Chen, M. Yoshita, A. Sato, T. Ito, H. Akiyama, and H. Yokoyama, “Dynamics of short-pulse generation via spectral filtering from intensely excited gain-switched 1.55-μm distributed-feedback laser diodes,” Opt. Express 21(9), 10597–10605 (2013). [CrossRef] [PubMed]

].

2. Experimental setup for picosecond pulse generation

Fig. 1 Schematic diagram of the experimental setup for strong gain switching (GS) of the 1064-nm distributed feedback laser diode (DFB-LD) and subsequent spectral handling.
We designed and fabricated a 1064-nm DFB-LD, having the high-frequency characteristics of a 13-GHz cut-off frequency. The active layer of the DFB-LD consisted of three InGaAs QWs. The device length was shortened to 250 μm to reduce the photon lifetime. Figure 1 shows a schematic diagram of the experimental setup for generating picosecond optical pulses by GS operation. The temperature of the LD was set to 20, 25, and 30°C by thermoelectric control. This temperature change resulted in a shift in the control laser oscillation wavelength, allowing the flexibility of the device to be tested with wavelength variation. Electrical pulses of 140-ps duration and 8-V amplitude were used to drive the DFB-LD for creating very high carrier densities necessary for short optical pulse generation. The GSLD pulse repetition rate was variable between 1 and 50 MHz in the present experimental setup. We mainly set the repetition rate of the electrical pulses at 10 MHz, a frequency appropriate for TPM applications. A low-power Yb-doped fiber amplifier (YDFA) was used to amplify the optical pulses before spectral filtering. This amplification was used for various optical measurements, including second harmonic generation (SHG) intensity autocorrelation to measure the optical pulse width. The spectrum of the amplified optical pulses was then processed using two different methods. The first method involved the extraction of the short-wavelength edge components using the BPF with sharp-edged filtering characteristics (full-width half-maximum (FWHM): 0.5 nm). The second method used spectral chirp compensation in the mid-wavelength region of the output spectrum. In this approach, a newly designed narrow-band CFBG, with a dispersion of −30 ps/nm and a reflection bandwidth of 0.3 nm, was used. The optical spectra and pulse widths were measured by an optical spectrum analyzer having a resolution bandwidth of 0.01 nm (Advantest Q8384) and an SHG intensity autocorrelator (Oyokoden Femtowave, model 980), respectively.

3. Short-pulse generation with the extraction of a short-wavelength edge component

Optical spectra for the outputs from the GSLD and the transmission curves of the tunable BPF are shown in Fig. 2(a) when the LD temperature was tuned to 20, 25, and 30°C. Figures 2(b) and 2(c) show the optical spectra and SHG intensity autocorrelation traces of the pulses after spectral filtering, respectively. For this pulse width measurement, the average optical power was set to 50 μW by controlling the YDFA gain. For all of the cases, the pulse duration was ~7.5 ps (using sech2 fitting) and the time-bandwidth product ranged from 0.39 to 0.46. These results demonstrate that nearly FTL 7.5-ps optical pulses were obtained by tuning of the BPF center wavelength; thus, the short-wavelength edge components experienced minimal spectral chirping. However, the present pulse width was longer than that of the 1.55-μm GSLD, which provided sub-5-ps optical pulses [11

11. S. Q. Chen, A. Sato, T. Ito, M. Yoshita, H. Akiyama, and H. Yokoyama, “Sub-5-ps optical pulse generation from a 1.55-µm distributed-feedback laser diode with nanosecond electric pulse excitation and spectral filtering,” Opt. Express 20(22), 24843–24849 (2012). [CrossRef] [PubMed]

]. One possible reason for this is that the response frequency of the present 1064-nm DFB-LD was lower than the 20-GHz value for the 1.55-μm DFB-LD.

Fig. 3 (a) SHG intensity autocorrelation traces and (b) central pass wavelength dependence of the optical pulse width for spectral filtering at various wavelengths.
Figures 3(a) and 3(b) show the SHG intensity autocorrelation traces and central pass wavelength dependence of the optical pulse width for spectral filtering at various wavelengths, respectively. The temperature of the LD was set to 25°C. The pulse width was below 8 ps in the short-wavelength region below 1064.5 nm. However, the pulse width increased as the central wavelength increased above 1064.5 nm. This increase in the pulse width indicates that the pulses undergo nonlinear down-chirping, as was also reported for the 1.55-μm GSLD [12

12. S. Q. Chen, M. Yoshita, A. Sato, T. Ito, H. Akiyama, and H. Yokoyama, “Dynamics of short-pulse generation via spectral filtering from intensely excited gain-switched 1.55-μm distributed-feedback laser diodes,” Opt. Express 21(9), 10597–10605 (2013). [CrossRef] [PubMed]

], because the shorter wavelength components of the optical pulses are emitted earlier in the transient lasing process.

4. Short-pulse generation with spectral chirp compensation

In another attempt to shorten the optical pulses generated from the 1064-nm GSLD, we extracted the mid-wavelength portion of the GSLD output spectrum and compensated for linear chirp using a CFBG. As explained in Sec. 3 the mid-wavelength portion has the frequency chirping in contrast to the short-wavelength edge component; therefore, the chirp compensation can result in obtaining optical pulses having temporal durations shorter than the initial value. For this purpose, we designed and fabricated a narrow-band CFBG, optimized for optical pulse generation from the present 1064-nm GSLD.

Fig. 4 (a) Optical spectra and (b) SHG intensity autocorrelation traces for the optical pulses reflected from the narrow-band chirped fiber Bragg grating (CFBG).
Figures 4(a) and 4(b) show the optical spectra and SHG intensity autocorrelation traces for the optical pulses reflected from the narrow-band CFBG, respectively, for three different LD temperatures (20, 25, and 30°C). The CFBG was designed to obtain the best performance for the 1064-nm LD temperature of 25°C. The corresponding SHG autocorrelation traces in Fig. 4(b) indicated that linear chirp compensation by the CFBG, having a dispersion of −30 ps/nm, worked well for the mid-portion of the optical spectrum at 25°C. Using a Gaussian-shaped fit, the resulting pulse width was measured at 7.1 ps. The time-bandwidth product of 0.47 indicated that the optical pulses were nearly FTL. In contrast, for LD operating temperatures of 20 and 30°C, the pulse widths were longer than 10 ps. Thus, the CFBG was not effective for the short- and long-wavelength components of the spectrum.

Taken together, the results showed that frequency chirping of the optical pulses generated from the strongly driven DFB-LD was quite nonlinear. However, the extraction of the short-wavelength edge components always produced non-chirped short pulses. The mid-wavelength portion of the GSLD output spectrum exhibited a linear down-chirping feature; this suggested that the appropriate combination of band extraction and linear chirp compensation could also produce FTL picosecond pulses.

5. Two-photon microscopy application of amplified 7-ps optical pulses

First, we observed paraformaldehyde (PFA)-fixed biological specimens to evaluate our amplified optical pulses as a trial imaging experiment. We performed TPM imaging on PFA-fixed brain slices of H-line mouse expressing enhanced yellow fluorescent protein (eYFP) in the neocortex layer V pyramidal neurons. Our two-photon microscope consisted of an inverted microscope (Olympus IX71) and a laser beam scanning unit (Olympus FV300). Figure 5 shows a picture of two-photon fluorescent imaging of the brain slices of the H-line mouse, obtained with 10-MHz amplified optical pulses. The 800 × 600 pixel picture was obtained from one scan (scan time: 3.8 s). Fine structures of the eYFP-expressing neurons were observed. The optical-pulse repetition rate dependence of the TPM images was also examined at 5, 10, 20, and 50 MHz. A brighter picture was obtained for a lower pulse repetition rate, reflecting the higher peak power of the optical pulses under a constant averaged optical power, as was previously demonstrated for fluorescent beads by using 774-nm optical pulses [4

4. H. Yokoyama, H.-C. Guo, T. Yoda, K. Takashima, K. Sato, H. Taniguchi, and H. Ito, “Two-photon bioimaging with picosecond optical pulses from a semiconductor laser,” Opt. Express 14(8), 3467–3471 (2006). [CrossRef] [PubMed]

]. It is noted that notable photon bleaching was not observed in these TPM imaging.
Fig. 5 Two-photon fluorescence imaging of the enhanced yellow fluorescent protein (eYFP)-expressing neurons in the PFA-fixed brain slices of the H-line mouse.

Fig. 6 In vivo deep two-photon fluorescence imaging of the eYFP-expressing neurons in the brain of the H-line mouse.
Next, we demonstrated in vivo deep TPM imaging of the H-line mouse brain expressing eYFP using a properly adjusted in vivo TPM setup [8

8. R. Kawakami, K. Sawada, A. Sato, T. Hibi, Y. Kozawa, S. Sato, H. Yokoyama, and T. Nemoto, “Visualizing hippocampal neurons with in vivo two-photon microscopy using a 1030 nm picoseconds pulse laser,” Sci. Reports 3, 1014 (2013).

]. We have successfully performed the in vivo imaging at the depth of several hundred micrometers. Figure 6 shows an in vivo TPM imaging at 600 μm depth in the brain of the H-line mouse. It took 8 s for obtaining this picture (512 × 512 pixels). The eYFP-expressing neorcotex layer V pyramidal neurons were clearly observed with high axial resolution and weak background.

The present results indicate that the 1-μm wavelength optical pulse source, based on a GSLD, has high potential for TPM applications, comparing favorably with optical sources based on mode-locked lasers including MLLDs. Operation stability and repetition rate flexibility, which arise from precise electronic control, provide additional advantages.

6. Conclusions

We have successfully generated 7-ps optical pulses by intensive GS operation of a 1064-nm DFB-LD, incorporating spectral filtering and chirp compensation. Two methods were examined for shortening the optical pulse duration: the first method extracted the short-wavelength edge components using a BPF; the second method involved frequency chirp compensation around the mid-wavelength portion of the broadened laser oscillation spectrum, using a narrow-band CFBG. Both methods resulted in a pulse duration of ~7 ps. However, in the case of short-wavelength edge extraction by a BPF, we confirmed that tuning of the BPF could follow the central wavelength shift of the DFB-LD for producing FTL optical pulses. This result indicates that the short-wavelength edge extraction method can be a universal scheme for FTL ultrashort optical pulse generation from a gain-switched DFB-LD. The CFBG method can provide better short pulse performance than a BPF, if the chirp compensation and bandwidth selection are properly designed.

After amplification of the 7-ps optical pulses to over 20-kW peak power, we adapted them for TPM of yellow fluorescent biological specimens. Clear two-photon imaging was confirmed for eYFP-expressing neurons in the fixed brain slices of the H-line mouse. Furthermore, a successful experiment was also confirmed for in vivo TPM imaging of the eYFP-expressing neurons in the deep region of the H-line mouse brain. These results indicate that the present GSLD technology can provide very promising picosecond optical pulse sources for TPM including in vivo deep three dimensional two-photon bio-imaging. The effectiveness of the flexible pulse repetition rate in GSLD has also been examined by showing that a lower repetition rate gives brighter images, reflecting the higher peak power of the optical pulses under a constant averaged optical power. Further progress in LD devices and GS technology would enable the generation of optical pulses of a few picoseconds duration in the wavelength region near 1 μm. Therefore, the present results indicate that the 1-μm band picosecond GSLD will be a core device for advanced optical pulse sources for TPM, providing a simple and reliable approach that can be controlled by high-speed electronics.

Acknowledgments

The authors thank S. Kanazawa and K. Sawada for their technical assistances. This work was supported by Core Research for Evolutional Science and Technology (CREST) Program “Optical science of vector beams and nano-imaging” from Japan Science and Technology Agency (JST), and Program for Creating STart-ups from Advanced Research and Technology (START) “Development of highly functional light sources for advanced biomedical photonics” from the Ministry of Education, Culture, Sports, Science and Technology (MEXT) of Japan.

References and links

1.

W. Denk, J. H. Strickler, and W. W. Webb, “Two-photon laser scanning fluorescence microscopy,” Science 248(4951), 73–76 (1990). [CrossRef] [PubMed]

2.

P. F. Curley, A. I. Ferguson, J. G. White, and W. B. Amos, “Application of a femtosecond self-sustained mode-locked Ti:sapphire laser to the field of laser scanning confocal microscopy,” Opt. Quantum Electron. 24(8), 851–859 (1992). [CrossRef]

3.

E. Spiess, F. Bestvater, A. Heckel-Pompey, K. Toth, M. Hacker, G. Stobrawa, T. Feurer, C. Wotzlaw, U. Berchner-Pfannschmidt, T. Porwol, and H. Acker, “Two-photon excitation and emission spectra of the green fluorescent protein variants ECFP, EGFP and EYFP,” J. Microsc. 217(3), 200–204 (2005). [CrossRef] [PubMed]

4.

H. Yokoyama, H.-C. Guo, T. Yoda, K. Takashima, K. Sato, H. Taniguchi, and H. Ito, “Two-photon bioimaging with picosecond optical pulses from a semiconductor laser,” Opt. Express 14(8), 3467–3471 (2006). [CrossRef] [PubMed]

5.

H. Yokoyama, H. Tsubokawa, H.-C. Guo, J. Shikata, K. Sato, K. Takashima, K. Kashiwagi, N. Saito, H. Taniguchi, and H. Ito, “Two-photon bioimaging utilizing supercontinuum light generated by a high-peak-power picosecond semiconductor laser source,” J. Biomed. Opt. 12(5), 054019 (2007). [CrossRef] [PubMed]

6.

H. Yokoyama, A. Sato, H.-C. Guo, K. Sato, M. Mure, and H. Tsubokawa, “Nonlinear-microscopy optical-pulse sources based on mode-locked semiconductor lasers,” Opt. Express 16(22), 17752–17758 (2008). [CrossRef] [PubMed]

7.

K. Plaetzer, B. Krammer, J. Berlanda, F. Berr, and T. Kiesslich, “Photophysics and photochemistry of photodynamic therapy: fundamental aspects,” Lasers Med. Sci. 24(2), 259–268 (2009). [CrossRef] [PubMed]

8.

R. Kawakami, K. Sawada, A. Sato, T. Hibi, Y. Kozawa, S. Sato, H. Yokoyama, and T. Nemoto, “Visualizing hippocampal neurons with in vivo two-photon microscopy using a 1030 nm picoseconds pulse laser,” Sci. Reports 3, 1014 (2013).

9.

C. L. Lin, P. L. Liu, T. C. Damen, D. J. Eilenberger, and R. L. Hartman, “Simple picosecond pulse generation scheme for injection lasers,” Electron. Lett. 16(15), 600–601 (1980). [CrossRef]

10.

H. Yokoyama, “Dynamics in gain-switched semiconductor lasers generating ultrashort optical pulses,” presented at OPTIC 2012, National Taiwan University, Taiwan, 6–8 Dec. (2012).

11.

S. Q. Chen, A. Sato, T. Ito, M. Yoshita, H. Akiyama, and H. Yokoyama, “Sub-5-ps optical pulse generation from a 1.55-µm distributed-feedback laser diode with nanosecond electric pulse excitation and spectral filtering,” Opt. Express 20(22), 24843–24849 (2012). [CrossRef] [PubMed]

12.

S. Q. Chen, M. Yoshita, A. Sato, T. Ito, H. Akiyama, and H. Yokoyama, “Dynamics of short-pulse generation via spectral filtering from intensely excited gain-switched 1.55-μm distributed-feedback laser diodes,” Opt. Express 21(9), 10597–10605 (2013). [CrossRef] [PubMed]

OCIS Codes
(140.3070) Lasers and laser optics : Infrared and far-infrared lasers
(140.3490) Lasers and laser optics : Lasers, distributed-feedback
(140.5960) Lasers and laser optics : Semiconductor lasers
(170.2520) Medical optics and biotechnology : Fluorescence microscopy
(140.3538) Lasers and laser optics : Lasers, pulsed

ToC Category:
Lasers and Laser Optics

History
Original Manuscript: November 29, 2013
Revised Manuscript: January 16, 2014
Manuscript Accepted: January 16, 2014
Published: March 5, 2014

Virtual Issues
Vol. 9, Iss. 5 Virtual Journal for Biomedical Optics

Citation
Yuta Kusama, Yuichiro Tanushi, Masami Yokoyama, Ryosuke Kawakami, Terumasa Hibi, Yuichi Kozawa, Tomomi Nemoto, Shunichi Sato, and Hiroyuki Yokoyama, "7-ps optical pulse generation from a 1064-nm gain-switched laser diode and its application for two-photon microscopy," Opt. Express 22, 5746-5753 (2014)
http://www.opticsinfobase.org/vjbo/abstract.cfm?URI=oe-22-5-5746


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References

  1. W. Denk, J. H. Strickler, W. W. Webb, “Two-photon laser scanning fluorescence microscopy,” Science 248(4951), 73–76 (1990). [CrossRef] [PubMed]
  2. P. F. Curley, A. I. Ferguson, J. G. White, W. B. Amos, “Application of a femtosecond self-sustained mode-locked Ti:sapphire laser to the field of laser scanning confocal microscopy,” Opt. Quantum Electron. 24(8), 851–859 (1992). [CrossRef]
  3. E. Spiess, F. Bestvater, A. Heckel-Pompey, K. Toth, M. Hacker, G. Stobrawa, T. Feurer, C. Wotzlaw, U. Berchner-Pfannschmidt, T. Porwol, H. Acker, “Two-photon excitation and emission spectra of the green fluorescent protein variants ECFP, EGFP and EYFP,” J. Microsc. 217(3), 200–204 (2005). [CrossRef] [PubMed]
  4. H. Yokoyama, H.-C. Guo, T. Yoda, K. Takashima, K. Sato, H. Taniguchi, H. Ito, “Two-photon bioimaging with picosecond optical pulses from a semiconductor laser,” Opt. Express 14(8), 3467–3471 (2006). [CrossRef] [PubMed]
  5. H. Yokoyama, H. Tsubokawa, H.-C. Guo, J. Shikata, K. Sato, K. Takashima, K. Kashiwagi, N. Saito, H. Taniguchi, H. Ito, “Two-photon bioimaging utilizing supercontinuum light generated by a high-peak-power picosecond semiconductor laser source,” J. Biomed. Opt. 12(5), 054019 (2007). [CrossRef] [PubMed]
  6. H. Yokoyama, A. Sato, H.-C. Guo, K. Sato, M. Mure, H. Tsubokawa, “Nonlinear-microscopy optical-pulse sources based on mode-locked semiconductor lasers,” Opt. Express 16(22), 17752–17758 (2008). [CrossRef] [PubMed]
  7. K. Plaetzer, B. Krammer, J. Berlanda, F. Berr, T. Kiesslich, “Photophysics and photochemistry of photodynamic therapy: fundamental aspects,” Lasers Med. Sci. 24(2), 259–268 (2009). [CrossRef] [PubMed]
  8. R. Kawakami, K. Sawada, A. Sato, T. Hibi, Y. Kozawa, S. Sato, H. Yokoyama, T. Nemoto, “Visualizing hippocampal neurons with in vivo two-photon microscopy using a 1030 nm picoseconds pulse laser,” Sci. Reports 3, 1014 (2013).
  9. C. L. Lin, P. L. Liu, T. C. Damen, D. J. Eilenberger, R. L. Hartman, “Simple picosecond pulse generation scheme for injection lasers,” Electron. Lett. 16(15), 600–601 (1980). [CrossRef]
  10. H. Yokoyama, “Dynamics in gain-switched semiconductor lasers generating ultrashort optical pulses,” presented at OPTIC 2012, National Taiwan University, Taiwan, 6–8 Dec. (2012).
  11. S. Q. Chen, A. Sato, T. Ito, M. Yoshita, H. Akiyama, H. Yokoyama, “Sub-5-ps optical pulse generation from a 1.55-µm distributed-feedback laser diode with nanosecond electric pulse excitation and spectral filtering,” Opt. Express 20(22), 24843–24849 (2012). [CrossRef] [PubMed]
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