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Tunable terahertz generation from one CO2 laser in a GaSe crystal
Optics Communications 284 (2011) 5472–5474
Contents lists available at SciVerse ScienceDirect
Optics Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / o p t c o m
Tunable terahertz generation from one CO2 laser in a GaSe crystal Zhiming Rao a, b, Xinbing Wang a,⁎, Yanzhao Lu a a b
Wuhan National Laboratory for Optoelectronics, College of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China Department of Computer Science, Jiangxi University of Traditional Chinese Medicine, Nanchang 330004, China
a r t i c l e
i n f o
Article history: Received 25 May 2011 Received in revised form 2 August 2011 Accepted 3 August 2011 Available online 22 August 2011 Keywords: Terahertz Difference frequency generation CO2 laser GaSe crystal
a b s t r a c t Coherent terahertz pulses have been generated at a range of 236.3–1104.5 μm (0.27–1.3 THz) by one CO2 laser with dual-wavelength output based on collinearly phase-matched different frequency generation (DFG) in a GaSe crystal. This source has the advantages of compact and simplicity for tuning. The output power of the THz pulse and phase-matching conditions were investigated. The maximum single pulse energy of 11 nJ was generated at a frequency of 1.23 THz (243.6 μm), corresponding to a peak output power 182 mW. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The generation of terahertz (THz) radiation at the frequency range of 0.3–10 THz continues to attract world-wide research interest. Many electronic and optical methods for THz generation have been established. Difference frequency generation (DFG) is one of the effective ways to produce high-power, tunable, and narrow-band coherent THz radiation in nonlinear crystals, such as ZnGeP2 [1], GaP [2], periodically poled LiNbO3 (PPLN) [3], GaSe [4], DAST [5], GaAs [6,7], and periodically-inverted GaAs [8,9]. DFG was designed to satisfy the wave vector phase matching condition in nonlinear crystal. GaSe is a semiconductor with layered hexagonal structure belonging 1 to the D3h (P6m2) space group, which is a promising crystal for THz generation. Its notable merits are high second-order nonlinear coefficient (d22 = 54 pm/V) and high transparency in both 0.62–18 μm band, and relatively high transparency in THz region. Again due to its large birefringence, GaSe can satisfy phase matching conditions for a variety of optical interactions. Furthermore, GaSe can be used to construct a simple THz-wave generation system as collinear phase matching DFG, which eliminates the complexity of angle tuning of both the input and output beams. But GaSe cannot be easily cut and polished, which causes a lot of Fresnel reflection loss of the input pump beam energy from the crystal surfaces. Recently, improvements in crystal growth technology have been developed for strengthening the optical and structure properties of GaSe [10], it is possible and effective to achieve cutting or polishing of GaSe. GaSe crystals have been demonstrated to be useful for parametric processes, for example, DFG
⁎ Corresponding author. E-mail address: [email protected] (X. Wang). 0030-4018/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2011.08.009
[4,11–13], second harmonic generators [10,14], and optical parametric generator [15]. In our laboratory, tunable third-harmonic and fourthharmonic generations of pulsed CO2 laser radiation in a GaSe crystal were demonstrated [16]. THz pulses have been obtained by DFG in GaSe crystals with the two input pulses wavelength of around 1 μm [4,11]. According to the Manley–Rowe relation, the maximum conversion efficiency can be improved by one order of magnitude with longer wavelength running at 10 μm. The highest average output power 260 μW of the THz pulse is achievable by frequency-mixing two CO2 laser lines near 10 μm in GaSe crystals [12]. However, which acquire THz source only one wavelength at 328.2 μm and the whole THz-wave generation system needs two CO2 lasers. In this paper, we demonstrate a tunable THz source based on the collinear DFG in a GaSe crystal with a dual-wavelength CO2 laser. This tunable THz source is pumped by a single CO2 laser, which is compact and easy to be established. This system can generate THz radiation in a range of 236.3–1104.5 μm (0.27–1.3 THz) in this study. 2. Experimental details This experimental setup for the THz generation is shown in Fig. 1. A self-made short pulsed TEA CO2 laser was used as the fundamental pump source. The laser had a discharge volume of 2 × 3 × 100 cm 3 with UV preionization and working at a maximum repetition rate of 10 Hz. Independent controls of multiline emission from a TEA CO2 laser have been established. The dual-wavelength CO2 laser system has the common output coupler, and two gratings were used as the end mirror grating arranged along direction having 3 cm length, and two laser lines oscillated independently in a shared discharge section, which profiles are square. The spot sizes of the orthogonally polarized beams are around 1 cm 2 at crystal input. The spatial overlapping is
Z. Rao et al. / Optics Communications 284 (2011) 5472–5474
45
M2
G2
CO2 laser HCT1 HCT2
λ2 λ1
Detector
THz
M1 BP
GaSe F
K1 K2
40
θ ext[deg]
BS
G1
5473
KTHz
experiment theory
35 30 25
Fig. 1. Experimental setup for THz generation based on collinear DFG a dualwavelength CO2 laser in a GaSe crystal. G1, G2, Gratings; M1, M2, mirrors; BS, beam splitter; BP, Brewster polarizer (transmittance of 95% for horizontally polarized wave and reflectivity of 95% for vertically polarized wave); F, quartz filter; HCT1–HCT2, HgCdTe detectors; Detector, Golay cell detector were used for THz energy detection.
20 15
200
400
600
800
1000
1200
THz wavelength[μ μm] around 0.9. Two laser beams propagated in parallel, both of which could be tuned from 9.2 μm to 10.7 μm by the two plane blazed gratings (150 lines/mm). The pulse energy of each line is around 100 mJ. The HgCdTe detectors HCT1 and HCT2 were used for the inspection of the time synchronization between the two CO2 laser lines. From Fig. 2, the full width at half maximum width (FWHM) pulses of the pump radiation was ~ 60 ns. Due to the orthogonal polarizations for the two beams, we have combined them using a Brewster polarizer, which has a transmittance of ~95% and a reflection of ~ 95% for the horizontally polarized and vertically polarized lasers beams, respectively. A quartz filter is placed before the detector to cutoff the transmitted pump beams and background radiation. We utilized a Golay cell (TYDEX, GC-1P) detector to detect the generated THz energy in this experiment. The 8 mm thick pure GaSe single crystal used in this study was supplied by MolTech GmbH Inc, and it was embedded in a cylindric holder with an aperture diameter of 15 mm. The optical axis of crystal lied in the vertical plane, and this crystal was grown with its surface perpendicular to the optical axis. As seen in the inset of Fig. 1, the collinear phase matching for DFG requires matching of the corresponding wave vectors k1 and k2 for the input frequencies ω1 and ω2, and the THz wave vector kT (at frequency ωT = ω1 − ω2) was used for the phase matching condition as k1 − k2 = kT. 3. Results and discussions
In Fig. 3, the theoretical and the experimental phase matching angles for THz generation is presented by mixing of CO2 laser lines in a collinearly type oe-e GaSe crystal. The empty circles were the measured PM angles in this experiment, and the triangles solid lines were calculated by the Sellmeier equations [17]. For mixing the 10.247 μm [10R(20) line] and 10.494 μm [10P(10) line] CO2 laser lines, which generated frequency at ~ 0.49THz(613.6 μm), the external PM angle was calculated to be 28.0° for the oe-e configuration. In this experiment, the external PM angle was measured to be 28.3° for the oe-e configuration, which is agreement with the theoretical result. As shown in Fig. 4, the experimental data on the spectra dependence of THz peak power is summarized. Efficient generation of coherent THz radiation was achieved in a GaSe crystal with tunability in a range of 236.3–1104.5 μm (0.27–1.3 THz) in Fig. 4. It can be seen that the output intensity at the frequency ~1.23 THz (243.6 μm) is much larger compared with other frequencies, and it decreases at higher frequency for increasing THz absorption coefficient of the GaSe crystal. The power intensity of the two unfocused laser beams is around 3 MW/cm 2. The measurement was performed by mixing the 10.247 μm [10R(20) line] and 10.697 μm [10P(30) line] CO2 laser lines resulting in the ~ 1.23 THz (243.6 μm) output, and the THz pulse detected about 11 nJ of pulse energy as the pulse duration of ~60 ns, which corresponding peak power of 182 mW. This peak power corresponds to be external power conversion efficiency about 1 × 10 − 5%. The relatively low output power and conversion efficiency could be caused by the reflection losses, the propagation losses of the terahertz waves, and the intrinsic defects of this GaSe crystal. For mixing the 10.247 μm [10R(20) line] and 10.551 μm [10P(16) line]
1.0
200
0.8
160
THz power [mW]
Normalized intensity
For type oe-e PM collinear DFG in the THz waveband, effective second-order nonlinear coefficient is given by: deff,oe-e = d22cos 2θ cos3φ, where θ and φ are the PM angle and azimuthal angle for the pump beams, respectively. To optimize second-order nonlinear coefficient, we set that azimuthal angle of φ = 0°.
Fig. 3. External phase-matching angle versus the generated THz wavelength.
0.6 0.4 0.2
120 80 40 0
0.0 -100
0
100
200
300
400
500
600
Time(ns) Fig. 2. Temporal waveforms of dual-wavelength CO2 laser pulses.
200
400
600
800
1000
1200
THz wavelength[μm] Fig. 4. Measured (triangles) DFG peak power in the THz range.
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Z. Rao et al. / Optics Communications 284 (2011) 5472–5474
1.0
Normalized THz signal
0.8
mismatch Sinc 2(ΔkL/2) function, where wave vector mismatch Δk = kT − k1 + k2 = ( nTωT − n1ω1 + n2ω2) / c b π/L and L is the length of the GaSe crystal, it is calculated about 0.8°. The measured value of the full width at half maximum width of the phase matching curve (diamonds in Fig. 5) was 1.2 ± 0.1°.
+ 0.1o Δ θ=1.2 -
0.6
4. Conclusion
0.4
0.2
0.0 37
38
39
40
41
42
θ ext [deg] Fig. 5. Phase-matching tuning curve for 1.23 THz radiation generated in a GaSe crystal pumping by CO2 laser lines. The diamonds are experimental data.
CO2 laser lines in the experiment, and a ~ 0.85 THz (355.1 μm) pulses was recorded peak power of 47 mW, which is about four times smaller than that of ~1.23 THz. We measured the terahertz polarizations by using a wire grid polarizer (MICROTECH, G25). The measured result of the maximum and minimum of the THz pulses at polarizer angle θ = 0°, 180° and θ = 90°, 270°, respectively, which are in agreement with theoretical calculations. In addition, due to the multimode structure of the pulsed CO2 laser, the bandwidths of the pump waves were 250 MHz (full width at half maximum) approximately. Therefore, the bandwidths of the THz waves should be narrower than pump waves. The angular acceptance angle is measured in this experiment. Fig. 5 shows the relative output power of the THz radiation versus the external phase matching angle for mixing the 10.247 μm and 10.697 μm beams. The output power peaked at 39.9° in oe-e PM scheme, which is in agreement with the calculated angle 40.1°. According to phase
In conclusion, using a compact dual-wavelength CO2 laser around 10 μm as DFG pumping source, we have implemented a novel compact THz source in one CO2 laser. Coherent terahertz pulses have been generated at a range of 236.3–1104.5 μm (0.27–1.3 THz) based on collinearly phase-matched DFG in GaSe crystal. A peak output power 182 mW was generated at a frequency of 1.23 THz. If a high quality GaSe was used in this experiment scheme, it is believed that a higher peak power and more widely tuning range of THz radiation could be realized. Acknowledgment This work is supported by the Creative Foundation of Wuhan National Laboratory for Optoelectronics (No. Z080007). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
V.V. Apollonov, Y.A. Shakir, Laser Phys. 9 (1999) 741. W. Shi, Y.J. Ding, Opt. Lett. 30 (2005) 1030. Y.S. Lee, T. Meade, et al., Appl. Phys. Lett. 76 (2000) 2505. W. Shi, Y.J. Ding, N. Fernelius, K. Vodopyanov, Opt. Lett. 27 (2002) 1454. K. Kawase, T. Hatanaka, et al., Opt. Lett. 25 (2000) 1714. S.Y. Tochitsky, C. Sung, et al., J. Opt. Soc. Am. B 24 (2007) 2509. Y. Lu, X. Wang, et al., Appl. Phys. B: Laser Opt. 103 (2011) 387. S.E. Trubnick, S.Y. Tochitsky, et al., Opt. Express 17 (2009) 2385. Y. Jiang, Y.J. Ding, L.B. Zotova, Appl. Phys. Lett. 93 (2008) 241102. S. Das, C. Ghosh, et al., Appl. Phys. B: Laser Opt. 82 (2006) 43. Y. Geng, X. Tan, X. Li, J. Yao, Appl. Phys. B: Laser Opt. 99 (2010) 181. Y. Jiang, Y.J. Ding, Appl. Phys. Lett. 91 (2007) 091108. K. Finsterbusch, A. Bayer, H. Zacharias, Appl. Phys. B: Laser Opt. 79 (2004) 457. Y.Z. Lu, X.B. Wang, et al., J. Appl. Phys. 107 (2010) 093105. G.C. Bhar, S. Das, K.L. Vodopyanov, Appl. Phys. B: Laser Opt. 61 (1995) 187. Y. Lu, X. Wang, et al., Opt. Cummun. 284 (2011) 3622. C.W. Chen, T.T. Tang, S.H. Lin, J.Y. Huang, et al., J. Opt. Soc. Am.B 26 (2009) 58.
Contents lists available at SciVerse ScienceDirect
Optics Communications j o u r n a l h o m e p a g e : w w w. e l s ev i e r. c o m / l o c a t e / o p t c o m
Tunable terahertz generation from one CO2 laser in a GaSe crystal Zhiming Rao a, b, Xinbing Wang a,⁎, Yanzhao Lu a a b
Wuhan National Laboratory for Optoelectronics, College of Optoelectronic Science and Engineering, Huazhong University of Science and Technology, Wuhan 430074, China Department of Computer Science, Jiangxi University of Traditional Chinese Medicine, Nanchang 330004, China
a r t i c l e
i n f o
Article history: Received 25 May 2011 Received in revised form 2 August 2011 Accepted 3 August 2011 Available online 22 August 2011 Keywords: Terahertz Difference frequency generation CO2 laser GaSe crystal
a b s t r a c t Coherent terahertz pulses have been generated at a range of 236.3–1104.5 μm (0.27–1.3 THz) by one CO2 laser with dual-wavelength output based on collinearly phase-matched different frequency generation (DFG) in a GaSe crystal. This source has the advantages of compact and simplicity for tuning. The output power of the THz pulse and phase-matching conditions were investigated. The maximum single pulse energy of 11 nJ was generated at a frequency of 1.23 THz (243.6 μm), corresponding to a peak output power 182 mW. © 2011 Elsevier B.V. All rights reserved.
1. Introduction The generation of terahertz (THz) radiation at the frequency range of 0.3–10 THz continues to attract world-wide research interest. Many electronic and optical methods for THz generation have been established. Difference frequency generation (DFG) is one of the effective ways to produce high-power, tunable, and narrow-band coherent THz radiation in nonlinear crystals, such as ZnGeP2 [1], GaP [2], periodically poled LiNbO3 (PPLN) [3], GaSe [4], DAST [5], GaAs [6,7], and periodically-inverted GaAs [8,9]. DFG was designed to satisfy the wave vector phase matching condition in nonlinear crystal. GaSe is a semiconductor with layered hexagonal structure belonging 1 to the D3h (P6m2) space group, which is a promising crystal for THz generation. Its notable merits are high second-order nonlinear coefficient (d22 = 54 pm/V) and high transparency in both 0.62–18 μm band, and relatively high transparency in THz region. Again due to its large birefringence, GaSe can satisfy phase matching conditions for a variety of optical interactions. Furthermore, GaSe can be used to construct a simple THz-wave generation system as collinear phase matching DFG, which eliminates the complexity of angle tuning of both the input and output beams. But GaSe cannot be easily cut and polished, which causes a lot of Fresnel reflection loss of the input pump beam energy from the crystal surfaces. Recently, improvements in crystal growth technology have been developed for strengthening the optical and structure properties of GaSe [10], it is possible and effective to achieve cutting or polishing of GaSe. GaSe crystals have been demonstrated to be useful for parametric processes, for example, DFG
⁎ Corresponding author. E-mail address: [email protected] (X. Wang). 0030-4018/$ – see front matter © 2011 Elsevier B.V. All rights reserved. doi:10.1016/j.optcom.2011.08.009
[4,11–13], second harmonic generators [10,14], and optical parametric generator [15]. In our laboratory, tunable third-harmonic and fourthharmonic generations of pulsed CO2 laser radiation in a GaSe crystal were demonstrated [16]. THz pulses have been obtained by DFG in GaSe crystals with the two input pulses wavelength of around 1 μm [4,11]. According to the Manley–Rowe relation, the maximum conversion efficiency can be improved by one order of magnitude with longer wavelength running at 10 μm. The highest average output power 260 μW of the THz pulse is achievable by frequency-mixing two CO2 laser lines near 10 μm in GaSe crystals [12]. However, which acquire THz source only one wavelength at 328.2 μm and the whole THz-wave generation system needs two CO2 lasers. In this paper, we demonstrate a tunable THz source based on the collinear DFG in a GaSe crystal with a dual-wavelength CO2 laser. This tunable THz source is pumped by a single CO2 laser, which is compact and easy to be established. This system can generate THz radiation in a range of 236.3–1104.5 μm (0.27–1.3 THz) in this study. 2. Experimental details This experimental setup for the THz generation is shown in Fig. 1. A self-made short pulsed TEA CO2 laser was used as the fundamental pump source. The laser had a discharge volume of 2 × 3 × 100 cm 3 with UV preionization and working at a maximum repetition rate of 10 Hz. Independent controls of multiline emission from a TEA CO2 laser have been established. The dual-wavelength CO2 laser system has the common output coupler, and two gratings were used as the end mirror grating arranged along direction having 3 cm length, and two laser lines oscillated independently in a shared discharge section, which profiles are square. The spot sizes of the orthogonally polarized beams are around 1 cm 2 at crystal input. The spatial overlapping is
Z. Rao et al. / Optics Communications 284 (2011) 5472–5474
45
M2
G2
CO2 laser HCT1 HCT2
λ2 λ1
Detector
THz
M1 BP
GaSe F
K1 K2
40
θ ext[deg]
BS
G1
5473
KTHz
experiment theory
35 30 25
Fig. 1. Experimental setup for THz generation based on collinear DFG a dualwavelength CO2 laser in a GaSe crystal. G1, G2, Gratings; M1, M2, mirrors; BS, beam splitter; BP, Brewster polarizer (transmittance of 95% for horizontally polarized wave and reflectivity of 95% for vertically polarized wave); F, quartz filter; HCT1–HCT2, HgCdTe detectors; Detector, Golay cell detector were used for THz energy detection.
20 15
200
400
600
800
1000
1200
THz wavelength[μ μm] around 0.9. Two laser beams propagated in parallel, both of which could be tuned from 9.2 μm to 10.7 μm by the two plane blazed gratings (150 lines/mm). The pulse energy of each line is around 100 mJ. The HgCdTe detectors HCT1 and HCT2 were used for the inspection of the time synchronization between the two CO2 laser lines. From Fig. 2, the full width at half maximum width (FWHM) pulses of the pump radiation was ~ 60 ns. Due to the orthogonal polarizations for the two beams, we have combined them using a Brewster polarizer, which has a transmittance of ~95% and a reflection of ~ 95% for the horizontally polarized and vertically polarized lasers beams, respectively. A quartz filter is placed before the detector to cutoff the transmitted pump beams and background radiation. We utilized a Golay cell (TYDEX, GC-1P) detector to detect the generated THz energy in this experiment. The 8 mm thick pure GaSe single crystal used in this study was supplied by MolTech GmbH Inc, and it was embedded in a cylindric holder with an aperture diameter of 15 mm. The optical axis of crystal lied in the vertical plane, and this crystal was grown with its surface perpendicular to the optical axis. As seen in the inset of Fig. 1, the collinear phase matching for DFG requires matching of the corresponding wave vectors k1 and k2 for the input frequencies ω1 and ω2, and the THz wave vector kT (at frequency ωT = ω1 − ω2) was used for the phase matching condition as k1 − k2 = kT. 3. Results and discussions
In Fig. 3, the theoretical and the experimental phase matching angles for THz generation is presented by mixing of CO2 laser lines in a collinearly type oe-e GaSe crystal. The empty circles were the measured PM angles in this experiment, and the triangles solid lines were calculated by the Sellmeier equations [17]. For mixing the 10.247 μm [10R(20) line] and 10.494 μm [10P(10) line] CO2 laser lines, which generated frequency at ~ 0.49THz(613.6 μm), the external PM angle was calculated to be 28.0° for the oe-e configuration. In this experiment, the external PM angle was measured to be 28.3° for the oe-e configuration, which is agreement with the theoretical result. As shown in Fig. 4, the experimental data on the spectra dependence of THz peak power is summarized. Efficient generation of coherent THz radiation was achieved in a GaSe crystal with tunability in a range of 236.3–1104.5 μm (0.27–1.3 THz) in Fig. 4. It can be seen that the output intensity at the frequency ~1.23 THz (243.6 μm) is much larger compared with other frequencies, and it decreases at higher frequency for increasing THz absorption coefficient of the GaSe crystal. The power intensity of the two unfocused laser beams is around 3 MW/cm 2. The measurement was performed by mixing the 10.247 μm [10R(20) line] and 10.697 μm [10P(30) line] CO2 laser lines resulting in the ~ 1.23 THz (243.6 μm) output, and the THz pulse detected about 11 nJ of pulse energy as the pulse duration of ~60 ns, which corresponding peak power of 182 mW. This peak power corresponds to be external power conversion efficiency about 1 × 10 − 5%. The relatively low output power and conversion efficiency could be caused by the reflection losses, the propagation losses of the terahertz waves, and the intrinsic defects of this GaSe crystal. For mixing the 10.247 μm [10R(20) line] and 10.551 μm [10P(16) line]
1.0
200
0.8
160
THz power [mW]
Normalized intensity
For type oe-e PM collinear DFG in the THz waveband, effective second-order nonlinear coefficient is given by: deff,oe-e = d22cos 2θ cos3φ, where θ and φ are the PM angle and azimuthal angle for the pump beams, respectively. To optimize second-order nonlinear coefficient, we set that azimuthal angle of φ = 0°.
Fig. 3. External phase-matching angle versus the generated THz wavelength.
0.6 0.4 0.2
120 80 40 0
0.0 -100
0
100
200
300
400
500
600
Time(ns) Fig. 2. Temporal waveforms of dual-wavelength CO2 laser pulses.
200
400
600
800
1000
1200
THz wavelength[μm] Fig. 4. Measured (triangles) DFG peak power in the THz range.
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Z. Rao et al. / Optics Communications 284 (2011) 5472–5474
1.0
Normalized THz signal
0.8
mismatch Sinc 2(ΔkL/2) function, where wave vector mismatch Δk = kT − k1 + k2 = ( nTωT − n1ω1 + n2ω2) / c b π/L and L is the length of the GaSe crystal, it is calculated about 0.8°. The measured value of the full width at half maximum width of the phase matching curve (diamonds in Fig. 5) was 1.2 ± 0.1°.
+ 0.1o Δ θ=1.2 -
0.6
4. Conclusion
0.4
0.2
0.0 37
38
39
40
41
42
θ ext [deg] Fig. 5. Phase-matching tuning curve for 1.23 THz radiation generated in a GaSe crystal pumping by CO2 laser lines. The diamonds are experimental data.
CO2 laser lines in the experiment, and a ~ 0.85 THz (355.1 μm) pulses was recorded peak power of 47 mW, which is about four times smaller than that of ~1.23 THz. We measured the terahertz polarizations by using a wire grid polarizer (MICROTECH, G25). The measured result of the maximum and minimum of the THz pulses at polarizer angle θ = 0°, 180° and θ = 90°, 270°, respectively, which are in agreement with theoretical calculations. In addition, due to the multimode structure of the pulsed CO2 laser, the bandwidths of the pump waves were 250 MHz (full width at half maximum) approximately. Therefore, the bandwidths of the THz waves should be narrower than pump waves. The angular acceptance angle is measured in this experiment. Fig. 5 shows the relative output power of the THz radiation versus the external phase matching angle for mixing the 10.247 μm and 10.697 μm beams. The output power peaked at 39.9° in oe-e PM scheme, which is in agreement with the calculated angle 40.1°. According to phase
In conclusion, using a compact dual-wavelength CO2 laser around 10 μm as DFG pumping source, we have implemented a novel compact THz source in one CO2 laser. Coherent terahertz pulses have been generated at a range of 236.3–1104.5 μm (0.27–1.3 THz) based on collinearly phase-matched DFG in GaSe crystal. A peak output power 182 mW was generated at a frequency of 1.23 THz. If a high quality GaSe was used in this experiment scheme, it is believed that a higher peak power and more widely tuning range of THz radiation could be realized. Acknowledgment This work is supported by the Creative Foundation of Wuhan National Laboratory for Optoelectronics (No. Z080007). References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15] [16] [17]
V.V. Apollonov, Y.A. Shakir, Laser Phys. 9 (1999) 741. W. Shi, Y.J. Ding, Opt. Lett. 30 (2005) 1030. Y.S. Lee, T. Meade, et al., Appl. Phys. Lett. 76 (2000) 2505. W. Shi, Y.J. Ding, N. Fernelius, K. Vodopyanov, Opt. Lett. 27 (2002) 1454. K. Kawase, T. Hatanaka, et al., Opt. Lett. 25 (2000) 1714. S.Y. Tochitsky, C. Sung, et al., J. Opt. Soc. Am. B 24 (2007) 2509. Y. Lu, X. Wang, et al., Appl. Phys. B: Laser Opt. 103 (2011) 387. S.E. Trubnick, S.Y. Tochitsky, et al., Opt. Express 17 (2009) 2385. Y. Jiang, Y.J. Ding, L.B. Zotova, Appl. Phys. Lett. 93 (2008) 241102. S. Das, C. Ghosh, et al., Appl. Phys. B: Laser Opt. 82 (2006) 43. Y. Geng, X. Tan, X. Li, J. Yao, Appl. Phys. B: Laser Opt. 99 (2010) 181. Y. Jiang, Y.J. Ding, Appl. Phys. Lett. 91 (2007) 091108. K. Finsterbusch, A. Bayer, H. Zacharias, Appl. Phys. B: Laser Opt. 79 (2004) 457. Y.Z. Lu, X.B. Wang, et al., J. Appl. Phys. 107 (2010) 093105. G.C. Bhar, S. Das, K.L. Vodopyanov, Appl. Phys. B: Laser Opt. 61 (1995) 187. Y. Lu, X. Wang, et al., Opt. Cummun. 284 (2011) 3622. C.W. Chen, T.T. Tang, S.H. Lin, J.Y. Huang, et al., J. Opt. Soc. Am.B 26 (2009) 58.