Products Home / Optical Elements / Nonlinear Crystals / BBO Crystals for Spontaneous Parametric Down ConversionBBO Crystals for Spontaneous Parametric Down Conversion
- Optimized for Type I and Type II Spontaneous Parametric Down Conversion
- Source for Polarization Entangled Photons or Heralded Single Photons
- Cut for Normal Incidence with 405 nm, 532 nm, or 775 nm Pump Lasers
- Available in Thicknesses of 1.00 mm, 2.00 mm, and 3.00 mm
When one of these β-BBO Crystals is mounted in the RSP1 mount, the crystal will be centered over the 8-32 (M4) hole in the mount's base without the need for spacers.
NLCQ1
1.00 mm Thick, θ = 29.2°
5.0 mm Aperture
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| Key Common Specificationsa | |
|---|---|
| Material | β-BBO (beta-BaB2O4) |
| Aperture | Ø5.0 mm |
| Clear Aperture | >Ø4.0 mm |
| Transmitted Wavefront Error | λ/3 @ 632.8 nm Over Clear Aperture |
| Surface Quality | 20-10 Scratch-Dig |
| Optic Axis Angleb Tolerance | ±0.5° |
Features
- β-BBO (beta-BaB2O4) Crystals Optimized for Spontaneous Parametric Down Conversion (SPDC)
- Type-I or Type-II SPDC
- Collinear and Noncollinear SPDC
- Designed for Use with 405 nm, 532 nm, or 775 nm Pump Lasers
- Markings on Housing Indicate Rotation Axis and Polarization Orientations
Thorlabs' β-BBO crystals for Spontaneous Parametric Down Conversion (SPDC) are designed for Type-I or Type-II SPDC, a nonlinear process where a single high-energy pump photon is down converted into a signal and idler pair of lower-energy photons, conserving both energy and momentum in the process. SPDC is commonly used as a source for polarization-entangled photon pairs or as a heralded single-photon source. Type-I SPDC outputs signal and idler photons with the same polarization, perpendicular to the pump polarization. Type-II SPDC outputs signal and idler photons with polarizations perpendicular to each other. Crystals are available for Type-I or Type-II SPDC, both collinear and noncollinear, designed for pump wavelengths of 405 nm, 532 nm, or 775 nm.
SPDC is the reverse process of sum frequency generation (SFG) and, in the degenerate case, second harmonic generation (SHG). As such, these BBO crystals are very similar to crystals designed for second harmonic generation. The primary difference is in the crystal lengths. Crystals for SHG are designed to match the group velocity walkoff of typical pulse durations. By contrast, the SPDC process is not limited in the same way. This allows for the use of thicker crystals that can provide greater efficiency (more signal/idler photon counts) at the cost of a blurring of the wavelength-position correlation of the photons. In order to support applications with differing requirements, these SPDC-optimized BBO crystals are available in thicknesses of 1.00 mm, 2.00 mm, and 3.00 mm.
Each crystal has an antireflection (AR) coating to provide low reflectance over the pump, signal, and idler wavelengths. For plots of the antireflection performance, see the Specs tab. The crystals are mounted in Ø1" housings that have a Ø5.0 mm aperture and engravings to aid in aligning the crystal with the polarization state and propagation direction of the input pump beam for phase matching (see Alignment for Optimal SPDC below).
To distinguish between pump and signal/idler photons (especially for collinear SPDC), a high optical density long-pass filter should be used. An optical density of 7 or greater is recommended which typically precludes the use of just a single filter. These crystals produce signal and idler photons with wavelengths in the visible to near infrared where single-photon detection is practical with detectors like the SPDMA Single Photon Detection Module.
Alignment for Optimal SPDC
The front of each crystal’s housing is engraved with the polarization orientations for the pump input beam (marked 2ω) and resulting orthogonally polarized SPDC-generated signal/idler beams (marked 1ω). A zero-order half-wave plate prior to the BBO crystal can be used to rotate the polarization of a linearly polarized pump beam to match the 2ω axis of the crystal. A line across the middle of the housing, labeled Rotation Axis, indicates the axis around which the crystal can be rotated in order to adjust the angle between the pump beam’s propagation direction and the optic axis of the crystal.
Thorlabs recommends mounting these crystals in an RSP1(/M) rotation mount attached to a manual rotation stage, such as Item # XRNR1(/M) or RP01(/M), as seen in the image to the left. When the crystal's housing is installed in the RSP1(/M) mount, the crystal will be centered over the 8-32 (M4) threaded hole in the bottom of the mount without the need to use spacers or additional retaining rings. This allows the crystal to be centered on the RP01(/M) rotation stage, which provides the fine control needed to optimize the phase matching angle by adjusting the angle of incidence. In this example case, the crystal is oriented for a horizontally polarized input pump beam.
To optimize the SPDC process in β-BBO, phase matching can be achieved by aligning the polarization of the pump input beam parallel to the crystal's principal extraordinary axis (marked 2ω), and then adjusting the angle between the optic axis and propagation direction to tune the phase matching, and thus the efficiency of the SPDC process. For each of the crystals below, the angle between the optic axis and the normal to the crystal surface was chosen so that phase matching would be optimized for normally incident light at the design wavelength listed in the tables below. Fine tuning in the range of ±1° around normal incidence will be necessary to achieve the desired collinear or non-collinear phase matching condition. Tuning to a greater angle allows for phase matching with a different wavelength pump laser; see the Specs tab for plots of tuning sensitivity.
Usage, Handling, and Care
Use care and always wear gloves when handling BBO crystals. These crystals scratch easily and the BBO is hygroscopic. Protect the crystals from excess moisture such as high humidity environments. In high-humidity environments, desiccant can help prolong the lifespan of the crystal. If needed, we recommend removing dust by gently puffing with clean dry air only, as detailed in the Blowing Off the Surface of an Optic section in our Optics Handling and Care Tutorial.
| Item # | NLCQ1 | NLCQ2 | NLCQ3 | NLCQ4 | NLCQ5 | NLCQ6 | NLCQ7 | NLCQ8 | NLC07 | |
|---|---|---|---|---|---|---|---|---|---|---|
| Material | β-BBO (beta-BaB2O4) | |||||||||
| Crystal Thickness | 1.00 mm | 2.00 mm | 3.00 mm | 1.00 mm | 2.00 mm | 3.00 mm | 3.00 mm | 3.00 mm | 3.00 mm | |
| Crystal Thickness Tolerance | ±0.05 mm | ±0.05 mm | ±0.05 mm | ±0.05 mm | ±0.05 mm | |||||
| Angle of Optic Axisa (θ) | 29.2° | 41.8° | 26.9° | 22.2° | 19.8° | |||||
| Optic Axis Anglea (θ) Tolerance | ±0.5° | ±0.5° | ±0.5° | ±0.5° | ±0.5° | |||||
| Application | Type-I SPDC | Type-II SPDC | Type-I SPDC | Type-I SPDC | Type-I SPDC | |||||
| Collinear vs Noncollinear | Both | Both | Collinear | Collinear | Both | |||||
| Pump Wavelength at AOI = 0° | 405 nm | 405 nm | 405 nm | 532 nm | 775 nm | |||||
| Signal Wavelength at AOI = 0° | 810 nm | 810 nm | 586 nm | 810 nm | 1550 nm | |||||
| Idler Wavelength at AOI = 0° | 810 nm | 810 nm | 1310 nm | 1550 nm | 1550 nm | |||||
| Angle of Incidence Tuning Sensitivityb |  |
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| AR Coating, Entrance Face, 0° AOI | R<0.5% at 405 and 810 nm | R<0.5% at 405 nm | R<1% at 532 nm | Ravg<4% 650 - 850 nm and 1300-1700 nm |
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| AR Coating, Exit Face, 0° AOI | R<3% at 586 and 1310 nm | R<2.5% at 810 and 1550 nm | ||||||||
| AR Coating Curves |  Raw Data |
 Raw Data |
 Raw Data |
 Raw Data |
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| Laser Induced Damage Threshold | 9.5 J/cm2 (532 nm, 5.3 ns, 100 Hz, Ø218 μm) | 0.6 J/cm2 (1550 nm, 52 fs FWHM, S-Pol, 104 Pulses) |
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| Aperture Diameter | Ø5.0 mm | |||||||||
| Clear Aperture | >Ø4.0 mm | |||||||||
| Mounted Diameter | 1" (25.4 mm) | |||||||||
| Surface Quality | 20-10 Scratch-Dig | |||||||||
| Transmitted Wavefront Error | λ/3 @ 632.8 nm Over Clear Aperture | |||||||||
| Physical and Optical Properties | ||
|---|---|---|
| Material | β-BBO (beta-BaB2O4) | |
| Crystal Structure | Trigonal, Space Group R3c | |
| Transparency Range | 189 - 3500 nm | |
| Second-Order Nonlinear Coefficients | d21 = 2.2 pm/V d31 = 0.08 pm/V d22 = 2.2 pm/V |
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| Nonlinear Refractive Index (Kerr Index)a | 4.9 x 10−20 m2/W @ 1032 nm | |
| Sellmeier Coefficientsb | Ordinary Ray |  |
| Extraordinary Ray |  |
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| Thermal Conductivity | 1.2 W / m ⋅ K (⊥ C) 1.6 W / m ⋅ K (|| C) |
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| Mohs Hardness | 4.5 Mohs | |
| Density | 3.85 g/cm3 | |
| Posted Comments: | |
| No Comments Posted |
Zoom| Key Specifications for SPDC Applicationsa | ||||
|---|---|---|---|---|
| Item # | NLCQ1 | NLCQ2 | NLCQ3 | |
| Crystal Thickness | 1.00 mm | 2.00 mm | 3.00 mm | |
| Angle of Optic Axis (θ)b | 29.2° ± 0.5° | |||
| Application | Type-I SPDC | |||
| AR Coating (AOI = 0°) | R<0.5% at 405 and 810 nm | |||
| AR Coating Curves | Raw Data |
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| Pump Wavelength (2ω) | AOI = 0° | 405 nm | ||
| SPDC Signal / Idler Wavelength (1ω) | AOI = 0° | 810 nm / 810 nm | ||
- Mounted Crystal with Antireflection (AR) Coating for 405 nm and 810 nm
- Optic Axis Angle of 29.2°
- Cut for a 405 nm Pump Wavelength and 810 nm Signal/Idler Wavelength at Normal Incidence
These β-BBO crystals are designed to produce 810 nm Type-I SPDC emission from an input beam with a center wavelength of 405 nm. They are available with thicknesses of 1.00, 2.00, or 3.00 mm and feature an AR coating to reduce surface reflections over the pump, signal, and idler wavelength ranges. These mounted crystals can be pumped with nanosecond lasers like Item # NPL41B, the frequency doubled output of Ti:sapphire lasers, or a 405 nm diode laser such as Item # L405P20.
Zoom| Key Specifications for SPDC Applicationsa | ||||
|---|---|---|---|---|
| Item # | NLCQ4 | NLCQ5 | NLCQ6 | |
| Crystal Thickness | 1.00 mm | 2.00 mm | 3.00 mm | |
| Angle of Optic Axis (θ)b | 41.8° ± 0.5° | |||
| Application | Type-II SPDC | |||
| AR Coating (AOI = 0°) | R<0.5% at 405 and 810 nm | |||
| AR Coating Curves | Raw Data |
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| Pump Wavelength (2ω) | AOI = 0° | 405 nm | ||
| SPDC Signal / Idler Wavelength (1ω) | AOI = 0° | 810 nm / 810 nm | ||
- Mounted Crystal with Antireflection (AR) Coating for 405 nm and 810 nm
- Optic Axis Angle of 41.8°
- Cut for a 405 nm Pump Wavelength and 810 nm Signal/Idler Wavelength at Normal Incidence
These β-BBO crystals are designed to produce 810 nm Type-II SPDC emission from an input beam with a center wavelength of 405 nm. They are available with thicknesses of 1.00, 2.00, or 3.00 mm and feature an AR coating to reduce surface reflections over the pump, signal, and idler wavelength ranges. These mounted crystals can be pumped with nanosecond lasers like Item # NPL41B, the frequency doubled output of Ti:sapphire lasers, or a 405 nm diode laser such as Item # L405P20.
Zoom| Key Specifications for SPDC Applicationsa | ||||
|---|---|---|---|---|
| Item # | NLCQ7 | |||
| Crystal Thickness | 3.00 mm | |||
| Angle of Optic Axis (θ)b | 26.9° ± 0.5° | |||
| Application | Type-I SPDC | |||
| AR Coating (AOI = 0°) | R<0.5% at 405 nm R<3% at 586 and 1310 nm |
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| AR Coating Curves | Raw Data |
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| Pump Wavelength (2ω) | AOI = 0° | 405 nm | ||
| SPDC Signal / Idler Wavelength (1ω) | AOI = 0° | 586 nm / 1310 nm | ||
- Mounted Crystal with Antireflection (AR) Coating for 405 nm, 586 nm, and 1310 nm
- Optic Axis Angle of 26.9°
- Cut for a 405 nm Pump Wavelength and 586/1310 nm Signal/Idler Wavelength at Normal Incidence
This β-BBO crystal is designed to produce 586 nm and 1310 nm Type-I SPDC emission from an input beam with a center wavelength of 405 nm. It is available with a thicknesses of 3.00 mm and features an AR coating to reduce surface reflections over the pump, signal, and idler wavelength ranges. This mounted crystal can be pumped with nanosecond lasers like Item # NPL41B, the frequency doubled output of Ti:sapphire lasers, or a 405 nm diode laser such as Item # L405P20.
Zoom| Key Specifications for SPDC Applicationsa | ||||
|---|---|---|---|---|
| Item # | NLCQ8 | |||
| Crystal Thickness | 3.00 mm | |||
| Angle of Optic Axis (θ)b | 22.2° ± 0.5° | |||
| Application | Type-I SPDC | |||
| AR Coating (AOI = 0°) | R<1% at 532 nm R<2.5% at 810 and 1550 nm |
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| AR Coating Curves | Raw Data |
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| Pump Wavelength (2ω) | AOI = 0° | 532 nm | ||
| SPDC Signal / Idler Wavelength (1ω) | AOI = 0° | 810 nm / 1550 nm | ||
- Mounted Crystal with Antireflection (AR) Coating for 532 nm, 810 nm, and 1550 nm
- Optic Axis Angle of 22.2°
- Cut for a 532 nm Pump Wavelength and 810/1550 nm Signal/Idler Wavelength at Normal Incidence
This β-BBO crystal is designed to produce 810 nm and 1550 nm Type-I SPDC emission from an input beam with a center wavelength of 532 nm. It is available with a thicknesses of 3.00 mm and features an AR coating to reduce surface reflections over the pump, signal, and idler wavelength ranges. This mounted crystal can be pumped with frequency doubled lasers at 532 nm and diode-pumped solid state lasers such as our Item # DJ532-40.
Zoom| Key Specifications for SPDC Applicationsa | ||||
|---|---|---|---|---|
| Item # | NLC07 | |||
| Crystal Thickness | 3.00 mm | |||
| Angle of Optic Axis (θ)b | 19.8° ± 0.5° | |||
| Application | Type-I SPDC | |||
| AR Coating (AOI = 0°) | Ravg<4%, 650 - 850 nm and 1300-1700 nm | |||
| AR Coating Curves | Raw Data |
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| Pump Wavelength (2ω) | AOI = 0° | 775 nm | ||
| SPDC Signal / Idler Wavelength (1ω) | AOI = 0° | 1550 nm / 1550 nm | ||
- Mounted Crystal with Antireflection (AR) Coating for 775 nm and 1550 nm
- Optic Axis Angle of 19.8°
- Cut for a 775 nm Pump Wavelength and 1550 nm Signal/Idler Wavelength at Normal Incidence
This β-BBO crystal is normally used for second harmonic generation (SHG) but in the reverse process also produces 1550 nm Type-I SPDC emission from an input beam with a center wavelength of 775 nm. It is available with a thicknesses of 3.00 mm and features an AR coating to reduce surface reflections over the pump, signal, and idler wavelength ranges. This mounted crystal can be pumped with a Ti:sapphire laser, a frequency doubled 1550 nm laser like Item # FSL1550, or diode lasers like Item # DBR780PN. This crystal can also be found on the BBO Crystals for Second Harmonic Generation page.
 β-BBO Crystals for SPDC |