Numerous nonlinear parametric applications, such as second harmonic generation, differential frequency production, and optical parametric amplification, require nonlinear optical (NLO) crystals. To employ a crystal for a particular purpose, the appropriate crystal must be chosen. In addition to transparency across the appropriate spectral range, it should also have high nonlinear coefficients, high optical damage thresholds, and enough birefringence for phase matching.
Alfa Chemistry customizes a range of NLO crystals for basic, applied research and industrial applications for optical frequency conversion applications from deep UV to far IR, covering a wide spectral range for nonlinear optical applications. Short lead times are possible for custom NLO crystals. We also provide bespoke coating for our customers. In case you have any urgent needs, kindly contact us.
Quality Customized Service
NLO custom crystals are produced using materials that have undergone rigorous quality control. Available materials include Lithium Triborate (LBO), Barium β-Borate (BBO), Cadmium Selenide (CdSe), Cadmium Sulfide (CdS), Potassium Titanyl Phosphate (KTP), Potassium Dihydrogen Phosphate (KDP), and Potassium Dideuterium Phosphate (KDP). Available crystal growth techniques include Stepanov, Czochralski (CZ), Kyropoulos, temperature gradient technique (TGT), and flux method.
Fig 1. Nonlinear microscopic images of 3D NPCs fabricated in a LiNbO3 crystal by femtosecond laser erasing of the second-order nonlinearity x(2). (Wei D, et al. 2018)
Custom NLO crystals include protective coatings that lessen reflections, shield against laser abrasion, and keep them from fogging in normal environments. For the most demanding intra- and extra-cavity applications, we employ advanced coating methods like ion beam sputtering (IBS) and ion assisted deposition (IAD) to deliver high damage thresholds and extremely low residual reflections. Additionally, NLO crystals crystals are also available in custom wavelengths and sizes.
Principles of NLO Crystals
What factors should a client consider when choosing an NLO crystal for a particular laser frequency conversion procedure? The main goal should be to achieve a high conversion efficiency. The conversion efficiency is related to the effective nonlinear coefficient (deff), crystal length (L), input power density (P) and phase mismatch (Dk) as follows:
hPL2(deffsin(DkL)/DkL)
It can be concluded that higher power density, longer crystal length, larger nonlinear coefficient and smaller phase mismatch will usually lead to higher conversion efficiency.
NLO crystals and lasers always have certain limits, though. For instance, the nonlinear crystal itself determines the deff, and the input power density must be below the crystal's damage threshold. Choosing the appropriate crystal for the customer's application is crucial. The following table contains the laser and crystal parameters we use to help our customers choose the best crystal.
| NLO crystal selection parameters | |
|---|---|
| Crystal Parameters | Laser Parameters |
| Phase-Matching Type and Angle, deff | NLO Process |
| Acceptance Angle | Divergence |
| Crystal Size, Walk-Off Angle | Beam Size |
| Damage Threshold | Power or Energy, Repetition Rate |
| Spectral Acceptance | Bandwidth |
| Group Velocity Mismatching | Pulse Width |
If you need technical advice, please contact our technical team to learn more about our high-quality services.
Reference
- Wei D, et al. (2018). "Experimental Demonstration of A Three-Dimensional Lithium Niobate Nonlinear Photonic Crystal." Nat. Photonics. 12: 596-600.