Theoretical and experimental studies on output characteristics of an intracavity KTA OPO

Dual-signal-resonant optical parametric oscillator intracavity driven by a coaxially end-pumped laser with compound gain media

A flexible method of generating stable dual-wavelength laser pulses with tunable power ratio and pulse interval is proposed, through integrating a coaxially end-pumped laser with compound gain media and an intracavity pumped optical parametric oscillator (IOPO). A theoretical model was built by a set of time-domain coupling wave equations containing both the generation of two fundamental waves from a shared pump source and the conversion to signal waves through the parametric process. Simulations showed that by simply varying the pump focal position or pump wavelength, the gains in two laser crystals could be changed, leading to simultaneous change in average power ratio and time interval between two wavelengths. Experimental verifications were performed with combined laser crystals (Nd:YAG and a-cut Nd:YLF) and a nonlinear crystal (KTA), which enabled dual-wavelength signal output in the 1.5-1.6 μm eye-safe region and demonstrated coincident conclusions with theoretical results. As there was no gain competition between two fundamental waves, stable signal output was obtained. Moreover, various wavelength pairs in any wavelength ranges are possible by using different laser crystals and nonlinear crystals. It is believed that this is a promising method for generating simultaneous dual-wavelength laser pulses for applications in lidar, remote sensing, nonlinear frequency conversion, etc.

Tunable KTA Stokes laser based on stimulated polariton scattering and its intracavity frequency doubling

This paper presents the tunable Stokes laser characteristics of KTiOAsO₄ (KTA) crystal based on stimulated polariton scattering (SPS). When the pumping laser wavelength is 1064.2 nm, the KTA Stokes wave can be discontinuously tuned from 1077.9 to 1088.4 nm with four gaps from 1079.0 to 1080.1 nm, from 1080.8 to 1082.8 nm, from 1083.6 to 1085.5 nm, and from 1085.8 to 1086.8 nm. When a frequency doubling crystal LiB₃O₅ (LBO) is inserted into the Stokes laser cavity, the frequency-doubled wave can be discontinuously tuned from 539.0 to 539.5 nm, from 540.1 to 540.4 nm, from 541.3 to 541.8 nm, from 542.7 to 542.9 nm and from 543.4 to 544.2 nm. With a pumping pulse energy of 130.0 mJ and an output coupler reflectivity of about 30%, the obtained maximum Stokes laser pulse energy at 1078.6 nm is 33.9 mJ and the obtained maximum frequency-doubled laser pulse energy at 543.8 nm is 15.7 mJ. By using the most probably coupled transverse optical modes obtained from the literature, the polariton refractive indexes, and the simplified polariton Sellmeier equations, the polariton dispersion curve is obtained. The formation of the Stokes frequency gaps is explained.

THz-wave generation via stimulated polariton scattering in KTiOAsO4 crystal

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.

Efficient RTP-based OPO intracavity pumped by an acousto-optic Q-switched Nd:YVO₄ laser

This Letter describes an intracavity pumped optical parametric oscillator (OPO) based on noncritical phase matching RbTiOPO4 (RTP) crystal driven by a laser diode end-pumping acousto-optic Q-switched Nd:YVO4 laser. Simultaneous efficient signal light at 1.6 μm and idler light at 3.1 μm outputs were obtained. At an incident pump power of 10.5 W and a Q-switching pulse repetition frequency of 60 kHz, 1.42 W at center wavelength of about 1619 nm and 0.38 W at 3108 nm were achieved, with the diode to OPO total output conversion efficiency up to 17.1%. The pulse width is about 6.5 ns for the signal light corresponding to the fundamental light at 1064 nm of about 10 ns. The spectral widths of the signal and idler light are narrower than 0.5 and 1.0 nm. The result shows that the RTP crystal is an efficient crystal to generate eye-safe and mid-infrared lights by making full use of noncritical phase matching.