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Second-harmonic generation (SHG), also known as frequency doubling, is the lowest-order wave-wave nonlinear interaction that occurs in various systems, including optical, radio, atmospheric, and magnetohydrodynamic systems. [1]
First, a photon is shot through a specialized nonlinear optical device: a beta barium borate (BBO) crystal. [3] This crystal converts the single photon into two entangled photons of lower frequency, a process known as spontaneous parametric down-conversion (SPDC). These entangled photons follow separate paths.
The crystals exist in the high-temperature α phase and low-temperature β phase, abbreviated as BBO; both phases are birefringent, and BBO is a common nonlinear optical material. Barium borate was discovered and developed by Chen Chuangtian and others of the Fujian Institute of Research on the Structure of Matter, Chinese Academy of Sciences .
Practically, frequency doubling is carried out by placing a nonlinear medium in a laser beam. While there are many types of nonlinear media, the most common media are crystals. Commonly used crystals are BBO (β-barium borate), KDP (potassium dihydrogen phosphate), KTP (potassium titanyl phosphate), and lithium niobate.
For high output power BBO crystals are used as frequency doublers; for lower powers, KTP is used. Output powers available are up to 5000 mW. Output powers available are up to 5000 mW. Conversion efficiency for producing 473 nm laser radiation is low with some of the best lab produced results coming in at 10–15% efficient at converting 946 nm ...
Blue DPSSLs use a nearly identical process, except that the 808 nm light is being converted by an Nd:YAG crystal to 946 nm light (selecting this non-principal spectral line of neodymium in the same Nd-doped crystals), which is then frequency-doubled to 473 nm by a beta barium borate (BBO) crystal or LBO crystal. Because of the lower gain for ...
In an OPA, the input is two light beams, of frequency ω p and ω s. The OPA will make the pump beam (ω p) weaker, and amplify the signal beam (ω s), and also create a new, so-called idler beam at the frequency ω i with ω p =ω s +ω i. In the OPA, the pump and idler photons usually travel collinearly through a nonlinear optical crystal.
In the basic double-slit experiment, a beam of light (usually from a laser) is directed perpendicularly towards a wall pierced by two parallel slit apertures.If a detection screen (anything from a sheet of white paper to a CCD) is put on the other side of the double-slit wall (far enough for light from both slits to overlap), a pattern of light and dark fringes will be observed, a pattern that ...