ZnTe / GaSe Terahertz Crystals | SIMTRUM Photonics Store

ZnTe (Zinc Telluride) Crystals have a few orientations. For Thz generation by optical rectification process, ZnTe with <110> orientation is used. Optical rectification is a difference frequency in media with large second order susceptibility. Optical rectification is also analogous to frequency doubling, where a polarization induced in the crystal is equal to the difference of the individual frequencies rather than their sum. This can be calculated by the relation cos(A)*cos(B) =[cos(A+B)+cos(A-B)]/2. Another way of describing optical rectification and frequency doubling is by considering the polarization induced in a medium at frequency 2w when the source is at frequency w. The generated pulse would then be the envelope of the optical pulse. Detection of the THz pulses happens in free-space electro-optic detection with another 110 orientated ZnTe crystal. By linear propagation of the Thz pulse and the visiblepulse through the ZnTe crystal, birefringence in ZnTe crystal is induced and i read out by a linearly polarized visible pulse. When both pulses are in the ZnTe crystal, the visible polarization will be rotated by the THz pulse. Utilizing a l/4 waveplate, a set of balanced photodiodes, and a beam-splitting polarizer,we are able to trace out the THz pulse amplitude by tracking the visible pulse polarization rotation after the ZnTe crystal at a range of delay time with regards to the THz pulse. The applications of ZnTe includes LED and laser diodes, solar cells, terahertz imaging, electro-optic detector, holographic interferometry, and laser optical phase conjugation devices.

Gallium Selenide (GaSe) is a non-linear single optical crystal that has a high non-linear coefficient, a wide transparency range and a high damge threshold. It is a well suited material for SHG in the mid-IR. The frequency doubling properties of GaSe were observed for the wavelength range of 6.0μm to 12μm.

Some areas of application include- SHG of CO2 laser (up to 9% conversion); SHG of pulsed CO, CO2 and chemical DF-laser (I = 2.36 μm) radiation; upconversion of CO and CO2 laser radiation into the visible light region; infrared pulses generation via frequency mixing of Neodymium and infrared dye laser or (F-)- centre laser pulses; OPG light generation within 3.5-18 μm; terahertz (T-rays) radiation generartion.

Since it is not possible to cut crystals for certain phase matching angles due to their material structure, this restricts the areas of applications.