Abstract
A terahertz parametric oscillator based on KTiOAsO(4) crystal is demonstrated for the first time. With the near-forward scattering configuration X(ZZ)X + Δφ, the polarizations of the pump, the Stokes and the generated THz waves are parallel to the z-axis of the crystal KTA. When the incident angle θext of the pump wave is changed from 1.875° to 6.500°, the THz wave is intermittently tuned from 3.59 to 3.96 THz, from 4.21 to 4.50 THz, from 4.90 to 5.16 THz, from 5.62 to 5.66 THz and from 5.92 to 6.43 THz. The obtained maximum THz wave energy is 627 nJ at 4.30 THz with a pump energy of 100 mJ. It is believed that the terahertz wave generation is caused by the stimulated scattering of the polaritons associated with the most intensive transverse A(1) mode of 233.8 cm(-1). Four much weaker transverse A(1) modes of 132.9 cm(-1), 156.3 cm(-1),175.1 cm(-1), and 188.4 cm(-1) cause four frequency gaps, from 3.97 THz to 4.20 THz, from 4.51 to 4.89 THz, from 5.17 to 5.61 THz and from 5.67 to 5.91 THz, respectively.
Highlights
KTiOAsO4 (KTA) is a prominent nonlinear optical crystal. It has a high optical damage threshold (> 1.2 GW/cm2 for 8 ns at 1064 nm) [1] and a high second-order nonlinear coefficient (d33 = 16.2 ± 1 pm/V measured with second harmonic generation of 1064 nm) [2]. It has been widely used in expanding the frequency range of lasers through nonlinear conversion processes, including second harmonic generation [3, 4], sum frequency generation [5], difference frequency generation [6], and optical parametric oscillator [7,8,9]
A surface-emitted Terahertz parametric oscillators (TPOs) based on crystal KTA has been proposed and demonstrated according to the experimental study on the angle-tuning characteristics of the Stokes wave in the stimulated polariton scattering
With the near-forward scattering configuration X(ZZ)X + Δφ, the polarization of the THz wave was measured along the z-axis of the crystal KTA
Summary
KTiOAsO4 (KTA) is a prominent nonlinear optical crystal. It has a high optical damage threshold (> 1.2 GW/cm for 8 ns at 1064 nm) [1] and a high second-order nonlinear coefficient (d33 = 16.2 ± 1 pm/V measured with second harmonic generation of 1064 nm) [2]. The transverse optical A1 modes are located at 111.5, 132.9, 156.3, 175.1, 188.4, 209.4 and 233.8 cm−1 and the 233.8 cm−1 mode has a very intense strength [13] It is because of the existence of the intense transverse optical A1 mode which is both infrared- and Raman-active that KTA crystal has the potential to generate THz wave based on stimulated polariton scattering [14, 15]. They were respectively coated for high reflectivity (R > 99.8%) and partial transmission (T = 5.2%) at the wavelength range from 1060 nm to 1100 nm Both the resonant cavity and the crystal KTA were fixed on a rotational stage, which was controlled to adjust the phase-matching angle θin between the pump and oscillating Stokes waves inside the crystal. The surface-emitted configuration of the KTA-TPO is employed below
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