Applications of PPKTP

Spontaneous Parametric Down-Conversion (SPDC)

SPDC is the underlying process used in quantum optics to generate entangled photons. In this process one pump photon is split into two entangled photons, called signal and idler. Our crystals can be tailored to produce entangled photons at your desired wavelength. It is possible to generate entangled photons with the same polarisation (Type 0) or with opposite polarisation (Type II). Type 0 generally offers a higher photon rate while type II offers a narrower spectral bandwidth.

We also offer aperiodic poled KTP (APKTP). These crystals have been designed to remove the spectral side-lobes from the normal sinc¬≤. This gives a higher spectral purity but reduces the photon rate. 

We aim to have the following crystals in stock for SPDC:


405 nm to 810 nm (Type 0)
405 nm to 810 nm (Type II)
532 nm to 1064 nm (Type 0)
775 nm to 1550 nm (Type 0)
775 to 1550 nm (Type II)


Backward Wave Optical Parametric Oscillator (BWOPO)

In a BWOPO the generated signal and idler are counter-propagating. This actually makes it possible to effectively have an OPO without the need for any mirrors or cavity. Instead of establishing the feedback by resonating the signal or idler, it is established by the backwards propagating beam.

While this might not sound like a tremendous advantage at first, the BWOPO actually brings multiple benefits:

  • No cavity makes it compact and robust
  • Highly efficient (>70% efficiency demonstrated)
  • Unique spectral properties (Forward wave mimics pump, backward wave narrow and almost independent of pump)
  • Usable with pulse durations above 200 ps (shorter is possible with reduced efficiency)

Second Harmonic and Sum Frequency Generation (SHG and SFG)

SFG is the process where two photons of different frequency or wavelength interact with the nonlinear material to generate a new photon with the combined energy of the initial photons. One special case of this is SHG where the two initial photons have the same wavelength. 

Both SHG and SFG can be used to generate light at wavelengths unobtainable by conventional lasers. 

We offer both Type 0 (all z-polarised beams) and Type II (mix of z- and y-polarised beams). Type 0 offer significantly higher nonlinearity.

Optical Parametric Oscillator and Amplifier (OPO and OPA)

These are the same process as SPDC but with pump levels much higher and are used in order to generate laser light at new wavelengths. In an OPO the nonlinear crystal is placed inside a cavity. This cavity normally resonates the signal or idler to establish a feedback mechanism. This improves the efficiency and spectral properties of the generated light. 

To amplify the output of an OPO (or other seed laser) one uses an OPA. The OPA is normally operated in a single pass configuration and allows for amplification to higher levels.

We offer PPKTP for any kinds of OPOs and OPAs. One of our specialties is to manufacture our unique 4 mm x 4 mm apertures which, in combination with the high damage threshold of PPKTP, is the perfect choice for high energy applications.