Potential of Sub-THz-Wave Generation in Li2B4O7 Nonlinear Crystal at Room and Cryogenic Temperatures

Abstract

Due to their high optical damage threshold, borate crystals can be used for the efficient nonlinear down-conversion of terawatt laser radiation into the terahertz (THz) frequency range of the electromagnetic spectrum. In this work, we carried out a thorough study of the terahertz optical properties of the lithium tetraborate crystal (Li2B4O7; LB4) at 295 and 77 K. Approximating the terahertz refractive index in the form of Sellmeier’s equations, we assessed the possibility of converting the radiation of widespread high-power laser sources with wavelengths of 1064 and 800 nm, as well as their second and third harmonics, into the THz range. It was found that four out of eight types of three-wave mixing processes are possible. The conditions for collinear phase matching were fulfilled only for the o − e → o type of interaction, while cooling the crystal to 77 K did not practically affect the phase-matching curves. However, a noticeable increase of birefringence in the THz range with cooling (from 0.12 to 0.16) led to an increase in the coherence length for o − o → e and e − e → e types of interaction, which are potentially attractive for the down-conversion of ultrashort laser pulses.

London Dispersion Effects on the Structure and Properties of Nonlinear Optical BiB3O6 Crystal

“…It can be diagonalized to give n x = 2.39, n y = 2.67, n z = 3.57, which may be compared with the measured refractive indices of n x = 2.4, n y = 2.6 and n z = 3.9 at RT [64] or n x = 2.37, n y = 2.71 and n z = 3.75 at 77 K [65] in the THz range (at around 0.2 THz, well below the lowest vibration frequencies ~4.2 THz and well above the piezoelectric resonances~several MHz of the BiBO crystal samples).…”

Single-Chip Switchable Dual-Wavelength Vertical External-Cavity Surface-Emitting Laser

“…The key to the advancement of terahertz technology is the availability of low-cost and compact terahertz sources. Difference frequency generation is a relatively mature technique for producing terahertz band output [12][13][14]. VECSELs have unique advantages, such as broad wavelength range, fine wavelength tuning, and a flexible external cavity structure, making them very suitable for difference frequency generation of terahertz sources [15].…”

Elastic-plastic properties of Li2B4O7 determined by nanoindentation

“…The research interest in the superionic conductor lithium tetraborate (Li 2 B 4 O 7 ) is determined by its broad prospects for use in nonlinear optical and piezoelectric devices. Lithium tetraborate is a promising nonlinear material for laser frequency conversion, including for generating the fourth and fifth harmonics of Nd:YAG lasers [1] and sub-terahertz radiation [2]. In addition, following Sahil et al [3] and Mehrabi et al [4], Li 2 B 4 O 7 crystals (doped with various impurities) have wide application possibilities in radiation dosimetry.…”