Superluminescent high-efficient parametric generation in PPLN crystal with pumping by a Q-switched mode locked Nd:YAG laser

Abstract

We present results on parametric superluminescence in a periodically poled lithium niobate crystal pumped by a train of 45 ps pulses using a Q-switched mode locked Nd:YAG laser. The conversion efficiency (with respect to the absorbed power) was ~83%. To the best of our knowledge, this is the highest efficiency obtained with powerful superluminescent parametric sources. At the average pumping power of the laser of ~0.5 W and repetition rates of 1 and 1.7 kHz, the peak total output powers were as high as 210 and 200 kW, and the powers of the idler wavelength (3.82 µm) were 55 and 50 kW. New lines in the visible and UV spectrum were observed and are explained. The experiments demonstrated that the spectral and angular characteristics of superluminescence are determined by the pumping laser. In particular, the line width of the signal wave was close to that of the pumping line at ~200 GHz, and the divergence of the signal and idler waves depended only on the convergence (divergence) angle of the pumping radiation (30 mrad) and was independent of the wavelength.

Subharmonic mode locking of a Q-switched Nd:YAG laser

“…The characteristics of this scheme related to obtaining superluminescent parametric generation on a lithium niobate crystal with a periodic domain structure (PPLN) are described in detail in Ref. [18]. In this work, the same experimental results were obtained: the conversion efficiency was 83% for absorbed pump power.…”

“…Approximately half of the pump power (λ = 1064 nm) remained unconverted and came out of the PPLN crystal. Because the time delay of the pump and signal pulses is lΔn=c ∼ 1.7 ps (where l is the length of the PPLN crystal, Δn is the difference in refractive indices at 1064 nm and in the region of 1475 nm, c is the speed of light) and it is much shorter than the duration of these pulses, and their divergences are equal [18] ; then, further frequency conversion in an additional nonlinear element to the 620 nm region is possible. For this purpose, a lens 6 with a focal length of 5 cm, a nonlinear LBO crystal 7, a prism 8, and a diaphragm 9 were introduced to separate radiation at wavelengths 620, 1064, and 1475 nm, as well as measuring equipment 10 and 11 (Ophir power meter, MDR-23 monochromator or Michelson interferometer).…”

A 6.5 ns gain-switched electro-optical Q-switched Nd:YAG laser by 885 nm laser diode pulsed-end pumping

“…The laser diode (LD) end-pumped 1064 nm pulsed Nd:YAG lasers with high-peak-power, short-pulse-width and highbeam-quality have played an important role in the laser radar, material processing, etc, and they also serve as the pumps for the optical parametric oscillator to generate lasers with other wavelengths [1][2][3][4].…”

“…Figure 1 shows the Nd:YAG energy level diagram. Conventional Nd:YAG lasers pumped at 808 nm suffer from heat-related processes, arising from the quantum defect between the pump energy level 4 F 5/2 and emitting energy level 4 F 3/2 , such as strong thermal lensing, which can lead to beam quality degradation, pump-induced stresses, which lead to birefringence, and crystal fracture at excessive heat loads. Nevertheless, the quantum defect can be decreased by pumping particles directly into the emitting level 4 F 3/2 , thus reducing the thermal effect.…”