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Optics Express

Optics Express

  • Editor: C. Martijn de Sterke
  • Vol. 19, Iss. 24 — Nov. 21, 2011
  • pp: 23689–23697
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Effects of two-photon absorption on terahertz radiation generated by femtosecond-laser excited photoconductive antennas

Chao-Kuei Lee, Chan-Shan Yang, Sung-Hui Lin, Shiuan-Hua Huang, Osamu Wada, and Ci-Ling Pan  »View Author Affiliations


Optics Express, Vol. 19, Issue 24, pp. 23689-23697 (2011)
http://dx.doi.org/10.1364/OE.19.023689


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Abstract

Terahertz (THz) radiation can be generated more efficiently from a low-temperature-grown GaAs (LT-GaAs) photoconductive (PC) antenna by considering the two-photon absorption (TPA) induced photo-carrier in the photoconductor. A rate-equation-based approach using the Drude-Lorentz model taking into account the band-diagram of LT-GaAs is used for the theoretical analysis. The use of transform-limited pulses at the PC antenna is critical experimentally. Previously unnoticed THz pulse features and anomalously increasing THz radiation power rather than saturation were observed. These are in good agreement with the theoretical predictions. The interplay of intensity dependence and dynamics of generation of photoexcited carriers by single-photon absorption and TPA for THz emission is discussed.

© 2011 OSA

1. Introduction

Since Auston’s group generated picosecond electromagnetic pulses from photoconductive (PC) antennas by ultrafast laser pulses several decades ago [1

1. D. H. Auston, K. P. Cheung, and P. R. Smith, “Picosecond photoconducting Hertzian dipoles,” Appl. Phys. Lett. 45(3), 284–286 (1984). [CrossRef]

], such coherent terahertz (THz) radiation has been studied extensively and generated by various methods, e.g., ultrafast switching of PC antennas, optical rectification in nonlinear crystals, surge-current at the semiconductor surface, charge oscillations in semiconductor quantum wells, coherent excitation of optical phonons, etc. Among them, the technique of generation and detection of THz radiation using the PC antenna is well-established and widely used for various applications [2

2. Y.-S. Lee, Principles of Terahertz Science and Technology (Springer, New York, 2009).

].

In this paper, we consider low-temperature-grown GaAs (LT-GaAs), of which the band diagram has been thoroughly investigated [10

10. S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith, “Ultrafast dynamics of nonlinear absorption in low-temperature-grown GaAs,” Appl. Phys. Lett. 68(18), 2544–2546 (1996). [CrossRef]

12

12. H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Refractive index and absorption changes in low-temperature-grown GaAs,” Opt. Commun. 155(1-3), 206–212 (1998). [CrossRef]

] as the PC. Using the rate-equation approach and the Drude-Lorentz model [13

13. P. U. Jepsen, R. H. Jacobsen, and S. R. Keiding, “Generation and detection of terahertz pulses from biased semiconductor antennas,” J. Opt. Soc. Am. B 13(11), 2424–2436 (1996). [CrossRef]

15

15. L. Duvillaret, F. Garet, J.-F. Roux, and J.-L. Coutaz, “Analytical modeling and optimization of terahertz time-domain spectroscopy experiments, using photoswitches as antennas,” IEEE J. Sel. Top. Quantum Electron. 7(4), 615–623 (2001). [CrossRef]

], we present detailed calculations of THz radiation generated from LT-GaAs antennas and compare with experiments. It will be shown that the THz power radiated from PC antennas will depend on the competition between TPA and SPA. Because TPA effect converts two photons to electron-hole pairs, this process has lower conversion efficiency for photoexcited carriers, comparing with SPA effect. By virtue of this mechanism, the peak amplitude of the THz field and total power of the THz radiation will begin to saturate. However, optically induced carriers still can be excited to the conduction band by TPA for sufficiently optical excitation fluence. We propose and demonstrate that this mechanism can help alleviate the saturation of THz radiation power if SPA only is considered. Besides, possibility of enhancement of higher-frequency spectral components of THz radiation by TPA is also discussed.

2. Theoretical analysis

The approach we adopted is based on the rate-equation analysis using the Drude-Lorentz model [13

13. P. U. Jepsen, R. H. Jacobsen, and S. R. Keiding, “Generation and detection of terahertz pulses from biased semiconductor antennas,” J. Opt. Soc. Am. B 13(11), 2424–2436 (1996). [CrossRef]

15

15. L. Duvillaret, F. Garet, J.-F. Roux, and J.-L. Coutaz, “Analytical modeling and optimization of terahertz time-domain spectroscopy experiments, using photoswitches as antennas,” IEEE J. Sel. Top. Quantum Electron. 7(4), 615–623 (2001). [CrossRef]

] of semiconductors. Specifically, we consider the LT-GaAs system [10

10. S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith, “Ultrafast dynamics of nonlinear absorption in low-temperature-grown GaAs,” Appl. Phys. Lett. 68(18), 2544–2546 (1996). [CrossRef]

12

12. H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Refractive index and absorption changes in low-temperature-grown GaAs,” Opt. Commun. 155(1-3), 206–212 (1998). [CrossRef]

], which has many interesting properties, including short carrier lifetime, high mobility, and high breakdown voltage. As a result, LT-GaAs are widely in ultrafast photonic devices. Previously, Benjamin and associates observed TPA effect in LT-GaAs and determined key parameters such as TPA coefficient and carrier trapping time by the optical pump-probe techniques and the Z-scan measurements [10

10. S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith, “Ultrafast dynamics of nonlinear absorption in low-temperature-grown GaAs,” Appl. Phys. Lett. 68(18), 2544–2546 (1996). [CrossRef]

12

12. H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Refractive index and absorption changes in low-temperature-grown GaAs,” Opt. Commun. 155(1-3), 206–212 (1998). [CrossRef]

].

The rate-equation for the dynamics of carriers in the PC antenna based on LT-GaAs are
dN(t)dt=IσBBhν(N0N)Nτ1(1NTNT0)+nτ3(1NN0)
(1)
dNT(t)dt=IσTBNThνNTτ2+Nτ1(1NTNT0)+nτ4(1NTNT0)
(2)
dn(t)dt=IσTBNThν+I2β2hνnτ3(1NN0)nτ4(1NTNT0)
(3)
where N is the number of carriers at the bottom of the conduction band, N0 is the saturation carrier density, NT is the number of carriers in the mid-gap states contributing to induced absorption, NT0 is saturated number density of trapped carrier in the mid-gap states, n is the number of carries excited to upper states in the conduction band, is the photon energy of the incident light, σBB is the cross section for band-to-band transitions, σTB is the cross section for the band-to-trap transitions, β is the TPA coefficient, τ1 is the carrier trapping time from the bottom of the conduction band to the mid-gap states, τ2 is the trap emptying time, τ3 is the hot carrier relaxation time from the upper states of the conduction band to the bottom of the conduction band, and τ4 is the carrier trapping time from the upper states of the conduction band to the mid-gap states.

According to the Drude-Lorentz Model [14

14. Z. Piao, M. Tani, and K. Sakai, “Carrier dynamics and terahertz radiation in photoconductive antennas,” Jpn. J. Appl. Phys. 39(Part 1, No. 1), 96–100 (2000). [CrossRef]

], the equation of motion of carriers is given by
dv(t)dt=v(t)τs+em*Eloc(t),
(4)
where v(t) is the average velocity of the carrier, Eloc(t) is the local electric field, τs is the momentum relaxation time, e is the charge of an electron, and m* is the effective mass of the electron. The local electric field is screened by the polarization induced by the space charges,
Elocl(t)=EbPsc(t)ηε,
(5)
where Eb is the applied bias electric field on the PC antenna, Psc is the polarization induced by the separation of the hole and electron, η is the geometrical factor for the PC antenna, and ε is the dielectric constant of the PC. The temporal evolution of polarization is then
dPsc(t)dt=Psc(t)τr+J(t),
(6)
where τr is the recombination time of carrier, and J(t) is the current density induced by photoexcited carriers of which the time derivative gives rise to the radiated THz field for the Hertzian dipole. Most of the parameters used in the calculation were taken from results of Benjamin’s group [10

10. S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith, “Ultrafast dynamics of nonlinear absorption in low-temperature-grown GaAs,” Appl. Phys. Lett. 68(18), 2544–2546 (1996). [CrossRef]

12

12. H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Refractive index and absorption changes in low-temperature-grown GaAs,” Opt. Commun. 155(1-3), 206–212 (1998). [CrossRef]

]. Specifically, N0 = 5×1018 cm−3, NT0 = 5×1019 cm2, σBB = 2.5×10−14 cm2, σTB = 5×10−16 cm2, and β = 35 cm/GW, as well as the relevant carrier relaxation times given by τ1 = 1 ps, τ2 = 1.5 ps, τ3 = 100 ps, τ4 = 300 fs. According to Jepsen and associates, τr is much longer than the carrier lifetime and ranging from 1 to 100 ps [13

13. P. U. Jepsen, R. H. Jacobsen, and S. R. Keiding, “Generation and detection of terahertz pulses from biased semiconductor antennas,” J. Opt. Soc. Am. B 13(11), 2424–2436 (1996). [CrossRef]

]. To simplify the calculation, we set τr ≈10 ps, which is larger than both τ1 (1 ps) and τ4 (300 fs). The other parameters of the PC antenna needed include τs = 30 fs,, Eb = 104 V/cm, η = 900, refractive index of LT-GaAs = 3.6, and m* = 0.067m0. The excitation wavelength is 800 nm and the pulse duration is 35 fs.

By changing the focused laser spot size on the PC antenna, we consider two regimes of photo-excitation. In the first regime, carriers in the valance band can only be excited to the bottom of the conduction band (SPA effect only). In the second regime, carriers can also be excited to the upper states of the conduction band, i.e., both SPA and TPA effects are considered. In Fig. 2(a)
Fig. 2 Simulation results of peak amplitudes of THz fields and total radiated powers for two scenarios: (i) Carriers can only be excited to the bottom of the band gap (SPA effect only, blue traces), or (ii) carriers can also be excited to the upper states of the conduction band (Both SPA and TPA effects are present, red traces). For the pump power considered, the focus spot size is assumed to be 10 μm in (a) and (b) and 5 μm in (c) and (d), respectively.
and Fig. 2(b), we show simulation results for relatively low excitation powers, corresponding to the case of 10μm-spot size in our experimental configuration. It can be seen that peak amplitudes of the THz fields and total radiated powers first increase linearly with pump power initially at lower power densities and then exhibit saturation behavior at higher excitation densities. If the TPA effect is considered, THz peak amplitude and power saturate faster. Because the conversion of photons into carriers by the TPA effect is much less efficiently than the SPA effect, the simulated result is reasonable. Figure 2(c) and Fig. 2(d) show the peak amplitude and total power as the spot size is further focused down to 5μm. Significantly, if the TPA effect is included, the THz peak amplitudes and total powers are expected to increase and exceed values predicted for photoexcitation by SPA only at higher pump powers. This anomalous increase can be attributed to that the carriers still can be excited to the conduction band by TPA effect. Further, we find a similar tendency of non-saturation or anomalous increase in THz power for various values of geometrical factor η from 1 to 1000. Increasing geometric factor η corresponds to decreasing screening field or higher saturation intensity [13

13. P. U. Jepsen, R. H. Jacobsen, and S. R. Keiding, “Generation and detection of terahertz pulses from biased semiconductor antennas,” J. Opt. Soc. Am. B 13(11), 2424–2436 (1996). [CrossRef]

]. This observation further corroborates our contention that the anomalous increase of THz is due to the TPA effect.

3. Experimental methods and results

Experimentally, we employ a typical antenna-based THz time-domain spectroscopy (THz-TDS) which has been described in detail previously [16

16. R.-P. Pan, C.-F. Hsieh, C.-L. Pan, and C.-Y. Chen, “Temperature-dependent optical constants and birefringence of nematic liquid crystal 5CB in the terahertz frequency range,” J. Appl. Phys. 103(9), 093523 (2008). [CrossRef]

]. The femtosecond laser is a mode-locked Ti:sapphire laser (Spectra Physics, Tsunami) with an average power of ~450mW at a repetition rate of 82 MHz producing ~35fs. Its central wavelength is 800nm and the bandwidth (full-width-at-half maximum; FWHM) is around 43nm. To agree with the assumptions of our simulations, we would like to ensure that the optical pulse incident on the PC antenna is transform-limited. This is realized by adopting an adaptive pulse shaper consisting of a pair of gratings (600 lines/mm), two concave reflectors with a focal length of f = 20cm, and a liquid crystal spatial light modulator (SLM) (Cambridge Research and Instrumentation Inc, SLM-128). The SLM consists of 128 phase-modulating elements 100µm-wide with a 3µm gap between adjacent pixels. The Freezing algorithm is used to adaptively feedback-control phase of the optical pulses [17

17. M. C. Chen, J. Y. Huang, Q. Yang, C. L. Pan, and J.-I. Chyi, “Freezing phase scheme for fast adaptive control and its application to characterization of femtosecond coherent optical pulses reflected from semiconductor saturable absorber mirrors,” J. Opt. Soc. Am. B 22(5), 1134–1142 (2005). [CrossRef]

]. We used second harmonic generation by a 300μm thick BBO crystal located at the antenna position as the feedback signal. The shaped femtosecond laser output is then split into two beams and guided to the emitting and receiving PC antennas, respectively. The PC dipole antenna is fabricated on the LT-GaAs sample with a 30 μm antenna length, 5 μm gap, 5 μm antenna width, and 10 μm transmission line width. Both antennas are mounted with Si hemispherical lenses.

Figure 5(a)
Fig. 5 Pump power dependencies of the THz peak amplitude. (a) The laser beam spot size is 10 μm. (b) The laser beam spot size is 5 μm.
describes pump power dependencies of the THz peak amplitudes when the laser beam is defocused to a spot size of 10 μm. Clearly, it is not essential to include contribution by TPA. However, for higher pump power density, our model predict that the peak amplitudes of THz fields to exhibit a plateau with excitation power from 20 to 30 mW, before a monotonic rise with pump intensity above ~30mW. Good qualitative agreement with the experimental trend is obtained, as shown in Fig. 5(b). We note that the pump pulse incident on the generating PC antenna in typical THz time-domain spectroscopy (THz-TDS) system is chirped since most components in the system are dispersive and not pre-compensated. This implies longer pulses, lower pump intensity and diminishing role played by TPA in conventional PC-Antenna-based THz-TDS. For a THz-TDS system employing a broadband source without pre-compensation, the TPA will play a diminishing role while SPA will totally dominate. That is the reason why anomalous increase rather than saturation of THz radiation is observed for the first time here with transform-limited excitation using the pulse shaping technique. From Benjamin’s model [10

10. S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith, “Ultrafast dynamics of nonlinear absorption in low-temperature-grown GaAs,” Appl. Phys. Lett. 68(18), 2544–2546 (1996). [CrossRef]

], relaxed carriers from bottom of the conduction band could be generated by either TPA or SPA. This indicates the complexity of screening field since there are three possible way for carrier relaxation. However, we can consider just the inter-band transitions because the carrier lifetime for intra-band transitions (τ3) is long. Increasing electron-phonon scattering due to the high phonon density caused by the phonon bottleneck effect in LT-GaAs [20

20. X. Q. Zhou, H. M. van Driel, W. W. Rühle, and K. Ploog, “Direct observation of a reduced cooling rate of hot carriers in the presence of nonequilibrium LO phonons in GaAs:As,” Phys. Rev. B Condens. Matter 46(24), 16148–16151 (1992). [CrossRef] [PubMed]

] could reduce the τ3 in LT-GaAs. At the pump intensity employed in this work, this mechanism should be negligible. Therefore, we argue that photo-induced carriers caused by SPA and TPA effects can be considered separately. It follows that the two-photon induced carriers will not enhance the screening effect by the SPA.

In our experiments employing 30fs-wide pulses, maxima excitation power is limited to 50mW due to the damage issue. We find that the peak amplitudes of the generated THz pulses increase by a factor of two when the excitation power increased from 30 to 50mW. We anticipate the use of transform-limited pulses 15 fs wide can be used to generate THz pulses with peak amplitude as high as four times compared to the present case of 30fs-wide pulses.

The pulse shaping system is used to provide transform-limited pulses through compensating not only linear but also high-order chirp. Although we can compensate linear chirp using prism pairs, residual higher-order chirp means broader-than-transform-limited pulses and lower peak power which would reduce the beneficial role played by TPA compared with the pulse compensated by pulse shaper. Nonetheless, TPA will play a role if the peak intensity is still high enough even if the excitation pulse is not transform-limited. In addition, maximum THz emission power is limited by the electrostatic energy stored in the photoconductive gap, the estimated value should be around the order of 108 w/cm2 [3

3. M. Tani, M. Herrmann, and K. Sakai, “Generation and detection of terahertz pulsed radiation with photoconductive antennas and its application to imaging,” Meas. Sci. Technol. 13(11), 1739–1745 (2002). [CrossRef]

]. Apparently, this value is much larger than the excitation density in our case (around 105 W/cm2). Therefore, the generated THz power does not exceed the electrostatic energy stored in the photoconductive gap. As for the overall efficiency, it is difficult to measure in our case because the higher spectral component have been filtered out during the detection by PC antenna sampling. However, we estimate the overall efficiency increased by a factor of 2 by transform-limited pulses at an excitation power of 50 mW (see Fig. 2 (d)).

4. Conclusions

In this work, feasibility of enhancing THz radiation power due to TPA induced photo-carrier in PC antennas is studied theoretically and experimentally. Features of the THz waveform associated with SPA and TPA are clearly identified for the first time. At low excitation power densities, TPA actually caused radiated THz power to decrease. When photocurrent due to SPA saturated, however, extra carriers can still be excited to the conduction band by TPA, if the exciting photon density is sufficiently high. Experimentally, using the pulse shaping technique, we observed an anomalously increasing radiated power rather than saturation. This is in good agreement with predictions of the theoretical predictions and simulation results. With transform-limited pulses at the PC antenna, TPA effect can be enhanced for higher-power excitation condition. We show that TPA effect can help to break through the limitation of generation of THz radiation power by the PC antenna due to SPA. Besides, possibility of enhancing the high-frequency spectral components of THz radiation by TPA is also discussed.

5. Acknowledgments

This work was financially supported by the various grants of National Science Council Taiwan (R.O.C.) (NSC98-2112-M-110-001-MY3, NSC96-2752-E-009-007-PAE and NSC96-2752-E-009-008-PAE). Sung-Hui Lin now works at the Taiwan Semiconductor Manufacturing Company. The authors would also like to thank Prof. L. Yan of the University of Maryland, Baltimore County for helpful discussions.

References and links

1.

D. H. Auston, K. P. Cheung, and P. R. Smith, “Picosecond photoconducting Hertzian dipoles,” Appl. Phys. Lett. 45(3), 284–286 (1984). [CrossRef]

2.

Y.-S. Lee, Principles of Terahertz Science and Technology (Springer, New York, 2009).

3.

M. Tani, M. Herrmann, and K. Sakai, “Generation and detection of terahertz pulsed radiation with photoconductive antennas and its application to imaging,” Meas. Sci. Technol. 13(11), 1739–1745 (2002). [CrossRef]

4.

J. T. Darrow, X.-C. Zhang, D. H. Auston, and J. D. Morse, “Saturation properties of large-aperture photoconducting antennas,” IEEE J. Quantum Electron. 28(6), 1607–1616 (1992). [CrossRef]

5.

P. K. Benicewicz and A. J. Taylor, “Scaling of terahertz radiation from large-aperture biased InP photoconductors,” Opt. Lett. 18(16), 1332–1334 (1993). [CrossRef] [PubMed]

6.

T. Loffler, Dissertation (JWG University of Frankfurt, Germany, 2003).

7.

M. Tani, S. Matsuura, K. Sakai, and S.-I. Nakashima, “Emission characteristics of photoconductive antennas based on low-temperature-grown GaAs and semi-insulating GaAs,” Appl. Opt. 36(30), 7853–7859 (1997). [CrossRef] [PubMed]

8.

R.-H. Chou, T.-A. Liu, and C.-L. Pan, “Analysis of terahertz pulses from large-aperture biased semi-insulating and arsenic-ion-implanted GaAs antennas,” J. Appl. Phys. 104(5), 053121 (2008). [CrossRef]

9.

F. Kadlec, H. Nemec, and P. Kuzel, “Optical two-photon absorption in GaAs measured by optical-pump terahertz-probe spectroscopy,” Phys. Rev. B 70(12), 125205 (2004). [CrossRef]

10.

S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith, “Ultrafast dynamics of nonlinear absorption in low-temperature-grown GaAs,” Appl. Phys. Lett. 68(18), 2544–2546 (1996). [CrossRef]

11.

H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Optical characterization of low-temperature-grown GaAs for ultrafast all-optical switching devices,” IEEE J. Quantum Electron. 34(8), 1426–1437 (1998). [CrossRef]

12.

H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Refractive index and absorption changes in low-temperature-grown GaAs,” Opt. Commun. 155(1-3), 206–212 (1998). [CrossRef]

13.

P. U. Jepsen, R. H. Jacobsen, and S. R. Keiding, “Generation and detection of terahertz pulses from biased semiconductor antennas,” J. Opt. Soc. Am. B 13(11), 2424–2436 (1996). [CrossRef]

14.

Z. Piao, M. Tani, and K. Sakai, “Carrier dynamics and terahertz radiation in photoconductive antennas,” Jpn. J. Appl. Phys. 39(Part 1, No. 1), 96–100 (2000). [CrossRef]

15.

L. Duvillaret, F. Garet, J.-F. Roux, and J.-L. Coutaz, “Analytical modeling and optimization of terahertz time-domain spectroscopy experiments, using photoswitches as antennas,” IEEE J. Sel. Top. Quantum Electron. 7(4), 615–623 (2001). [CrossRef]

16.

R.-P. Pan, C.-F. Hsieh, C.-L. Pan, and C.-Y. Chen, “Temperature-dependent optical constants and birefringence of nematic liquid crystal 5CB in the terahertz frequency range,” J. Appl. Phys. 103(9), 093523 (2008). [CrossRef]

17.

M. C. Chen, J. Y. Huang, Q. Yang, C. L. Pan, and J.-I. Chyi, “Freezing phase scheme for fast adaptive control and its application to characterization of femtosecond coherent optical pulses reflected from semiconductor saturable absorber mirrors,” J. Opt. Soc. Am. B 22(5), 1134–1142 (2005). [CrossRef]

18.

S.-G. Park, M. R. Melloch, and A. M. Weiner, “Analysis of terahertz waveforms measured by photoconductive and electrooptic sampling,” IEEE J. Quantum Electron. 35(5), 810–819 (1999). [CrossRef]

19.

E. Castro-Camus, L. Fu, J. Lloyd-Hughes, H. H. Tan, C. Jagadish, and M. B. Johnston, “Photoconductive response correction for detectors of terahertz radiation,” J. Appl. Phys. 104(5), 053113 (2008). [CrossRef]

20.

X. Q. Zhou, H. M. van Driel, W. W. Rühle, and K. Ploog, “Direct observation of a reduced cooling rate of hot carriers in the presence of nonequilibrium LO phonons in GaAs:As,” Phys. Rev. B Condens. Matter 46(24), 16148–16151 (1992). [CrossRef] [PubMed]

21.

P. C. Upadhya, W. Fan, A. Burnett, J. Cunningham, A. G. Davies, E. H. Linfield, J. Lloyd-Hughes, E. Castro-Camus, M. B. Johnston, and H. Beere, “Excitation-density-dependent generation of broadband terahertz radiation in an asymmetrically excited photoconductive antenna,” Opt. Lett. 32(16), 2297–2299 (2007). [CrossRef] [PubMed]

OCIS Codes
(160.5140) Materials : Photoconductive materials
(320.0320) Ultrafast optics : Ultrafast optics
(300.6495) Spectroscopy : Spectroscopy, teraherz

ToC Category:
Ultrafast Optics

History
Original Manuscript: September 6, 2011
Revised Manuscript: October 6, 2011
Manuscript Accepted: October 6, 2011
Published: November 7, 2011

Citation
Chao-Kuei Lee, Chan-Shan Yang, Sung-Hui Lin, Shiuan-Hua Huang, Osamu Wada, and Ci-Ling Pan, "Effects of two-photon absorption on terahertz radiation generated by femtosecond-laser excited photoconductive antennas," Opt. Express 19, 23689-23697 (2011)
http://www.opticsinfobase.org/oe/abstract.cfm?URI=oe-19-24-23689


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References

  1. D. H. Auston, K. P. Cheung, and P. R. Smith, “Picosecond photoconducting Hertzian dipoles,” Appl. Phys. Lett.45(3), 284–286 (1984). [CrossRef]
  2. Y.-S. Lee, Principles of Terahertz Science and Technology (Springer, New York, 2009).
  3. M. Tani, M. Herrmann, and K. Sakai, “Generation and detection of terahertz pulsed radiation with photoconductive antennas and its application to imaging,” Meas. Sci. Technol.13(11), 1739–1745 (2002). [CrossRef]
  4. J. T. Darrow, X.-C. Zhang, D. H. Auston, and J. D. Morse, “Saturation properties of large-aperture photoconducting antennas,” IEEE J. Quantum Electron.28(6), 1607–1616 (1992). [CrossRef]
  5. P. K. Benicewicz and A. J. Taylor, “Scaling of terahertz radiation from large-aperture biased InP photoconductors,” Opt. Lett.18(16), 1332–1334 (1993). [CrossRef] [PubMed]
  6. T. Loffler, Dissertation (JWG University of Frankfurt, Germany, 2003).
  7. M. Tani, S. Matsuura, K. Sakai, and S.-I. Nakashima, “Emission characteristics of photoconductive antennas based on low-temperature-grown GaAs and semi-insulating GaAs,” Appl. Opt.36(30), 7853–7859 (1997). [CrossRef] [PubMed]
  8. R.-H. Chou, T.-A. Liu, and C.-L. Pan, “Analysis of terahertz pulses from large-aperture biased semi-insulating and arsenic-ion-implanted GaAs antennas,” J. Appl. Phys.104(5), 053121 (2008). [CrossRef]
  9. F. Kadlec, H. Nemec, and P. Kuzel, “Optical two-photon absorption in GaAs measured by optical-pump terahertz-probe spectroscopy,” Phys. Rev. B70(12), 125205 (2004). [CrossRef]
  10. S. D. Benjamin, H. S. Loka, A. Othonos, and P. W. E. Smith, “Ultrafast dynamics of nonlinear absorption in low-temperature-grown GaAs,” Appl. Phys. Lett.68(18), 2544–2546 (1996). [CrossRef]
  11. H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Optical characterization of low-temperature-grown GaAs for ultrafast all-optical switching devices,” IEEE J. Quantum Electron.34(8), 1426–1437 (1998). [CrossRef]
  12. H. S. Loka, S. D. Benjamin, and P. W. E. Smith, “Refractive index and absorption changes in low-temperature-grown GaAs,” Opt. Commun.155(1-3), 206–212 (1998). [CrossRef]
  13. P. U. Jepsen, R. H. Jacobsen, and S. R. Keiding, “Generation and detection of terahertz pulses from biased semiconductor antennas,” J. Opt. Soc. Am. B13(11), 2424–2436 (1996). [CrossRef]
  14. Z. Piao, M. Tani, and K. Sakai, “Carrier dynamics and terahertz radiation in photoconductive antennas,” Jpn. J. Appl. Phys.39(Part 1, No. 1), 96–100 (2000). [CrossRef]
  15. L. Duvillaret, F. Garet, J.-F. Roux, and J.-L. Coutaz, “Analytical modeling and optimization of terahertz time-domain spectroscopy experiments, using photoswitches as antennas,” IEEE J. Sel. Top. Quantum Electron.7(4), 615–623 (2001). [CrossRef]
  16. R.-P. Pan, C.-F. Hsieh, C.-L. Pan, and C.-Y. Chen, “Temperature-dependent optical constants and birefringence of nematic liquid crystal 5CB in the terahertz frequency range,” J. Appl. Phys.103(9), 093523 (2008). [CrossRef]
  17. M. C. Chen, J. Y. Huang, Q. Yang, C. L. Pan, and J.-I. Chyi, “Freezing phase scheme for fast adaptive control and its application to characterization of femtosecond coherent optical pulses reflected from semiconductor saturable absorber mirrors,” J. Opt. Soc. Am. B22(5), 1134–1142 (2005). [CrossRef]
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