BBO Crystals for Second Harmonic Generation


  • Tunable Fundamental and Second Harmonic Wavelengths
  • Ultrathin Contacted Crystals Down to 30 µm Thick
  • Free-Standing Crystals Up to 3 mm Thick
  • Ø5.0 mm Aperture in a Ø1" Housing

NCL01

NLC01

0.15 mm Thick, θ = 30.5°, 5.0 mm Aperture

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.

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Key Common Specificationsa
Material β-BBO (beta-BaB2O4)
Aperture Ø5.0 mm
Clear Aperture >80% of Diameter
Transmitted Wavefront Error λ/3 @ 632.8 nm Over Clear Aperture
Surface Quality 20-10 Scratch-Dig
Optic Axis Angleb Tolerance ±0.5°
  • See the Specs tab for complete specifications.
  • Angle Between Crystal's Surface Normal and Optic Axis
'Light from the FSL1030X2 laser passing through an NLC05 crystal.
Click to Enlarge
View Imperial Product List
Item #QtyDescription
FSL1030X21Ytterbium Femtosecond Fiber Laser, 1030 nm, 2 µJ, <130 fs Typ. Pulse Width
NLC051Ø1" Mounted β-BBO Crystal, 1.00 mm Thick, θ = 23.3°, 900 - 1300 nm Fund., 450 - 650 nm SHG
RSP11Rotation Mount for Ø1" (25.4 mm) Optics, 8-32 Tap
LA4158-B1f = 250 mm, Ø1" UVFS Plano-Convex Lens, ARC: 650 - 1050 nm
UBS241Ø1" Low-GDD Beamsplitter for Second Harmonic of Ultrafast Yb Lasers
FESH10001Ø25.0 mm Shortpass Filter, Cut-Off Wavelength: 1000 nm
PM100D1Compact Power and Energy Meter Console, Digital 4" LCD
S350C1Thermal Power Sensor Head, Surface Absorber, 0.19 - 1.1 µm and 10.6 µm, 10 mW - 40 W, Ø40 mm
S425C-L1Thermal Power Sensor Head, Surface Absorber, 0.19 - 20 µm, 2 mW - 50 W, Ø25.4 mm
LMR13Lens Mount with Retaining Ring for Ø1" Optics, 8-32 Tap
PH33Ø1/2" Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L = 3"
PH1.52Ø1/2" Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L = 1.5"
TR4-P51Ø1/2" Optical Post, SS, 8-32 Setscrew, 1/4"-20 Tap, L = 4", 5 Pack
BE1-P51Ø1.25" Studded Pedestal Base Adapter, 1/4"-20 Thread, 5 Pack
CF125-P51Clamping Fork, 1.24" Counterbored Slot, Universal, 5 Pack
View Metric Product List
Item #QtyDescription
FSL1030X21Ytterbium Femtosecond Fiber Laser, 1030 nm, 2 µJ, <130 fs Typ. Pulse Width
NLC051Ø1" Mounted β-BBO Crystal, 1.00 mm Thick, θ = 23.3°, 900 - 1300 nm Fund., 450 - 650 nm SHG
RSP1/M1Rotation Mount for Ø1" (25.4 mm) Optics, M4 Tap
LA4158-B1f = 250 mm, Ø1" UVFS Plano-Convex Lens, ARC: 650 - 1050 nm
UBS241Ø1" Low-GDD Beamsplitter for Second Harmonic of Ultrafast Yb Lasers
FESH10001Ø25.0 mm Shortpass Filter, Cut-Off Wavelength: 1000 nm
PM100D1Compact Power and Energy Meter Console, Digital 4" LCD
S350C1Thermal Power Sensor Head, Surface Absorber, 0.19 - 1.1 µm and 10.6 µm, 10 mW - 40 W, Ø40 mm
S425C-L1Thermal Power Sensor Head, Surface Absorber, 0.19 - 20 µm, 2 mW - 50 W, Ø25.4 mm
LMR1/M3Lens Mount with Retaining Ring for Ø1" Optics, M4 Tap
PH75/M3Ø12.7 mm Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L=75 mm
PH40/M2Ø12.7 mm Post Holder, Spring-Loaded Hex-Locking Thumbscrew, L=40 mm
TR100/M-P51Ø12.7 mm Optical Post, SS, M4 Setscrew, M6 Tap, L = 100 mm, 5 Pack
BE1/M-P51Ø31.8 mm Studded Pedestal Base Adapter, M6 Thread, 5 Pack
CF125-P51Clamping Fork, 1.24" Counterbored Slot, Universal, 5 Pack

The image above shows the light from an FSL1030X2 fiber laser passing through an NLC05 crystal, with the UBS24 beamsplitter filtering out the second harmonic.

Features

  • β-BBO (beta-BaB2O4) Crystals Optimized for Type-I Second Harmonic Generation (SHG)
  • Four Wavelength Range Options:
    • 680 - 900 nm (Fundamental) & 340 - 450 nm (SHG)
    • Ultrathin 700 - 1200 nm (Fundamental) & 350 - 600 nm (SHG)
    • 900 - 1300 nm (Fundamental) & 450 - 650 nm (SHG)
    • 1300 - 1700 nm (Fundamental) & 650 - 850 nm (SHG)
  • Phase Matching Conditions Specified at or Near Normal Angle of Incidence
  • Markings on Housing Indicate Rotation Axis and Polarization Orientation
  • Options Include Crystals Optimized for Ti:Sapphire, Erbium (Er), and Ytterbium (Yb) Lasers
  • Designed for Use with Femtosecond Laser Pulses
  • Room Temperature Operation

Thorlabs' β-BBO Second Harmonic Crystals for Femtosecond Pulsed Lasers are tunable over a broad wavelength range to provide efficient second harmonic generation (SHG). SHG is a nonlinear process where two photons with the same fundamental wavelength are converted into a single SHG photon with half the wavelength. These uniaxial nonlinear crystals are frequently used to double the output of Ti:sapphire lasers (such as the Tiberius and Octavius lasers), few-cycle lasers, green-pumped and broadband optical parametric oscillators and amplifiers (OPOs and OPAs), as well as both ytterbium and erbium laser systems.

Pulse parameter information, including recommended minimum pulse durations and focal spot sizes, is provided. Each crystal has an antireflective (AR) coating to provide low reflectance over the fundamental and second harmonic wavelength ranges. To support pulsed laser applications, the crystals are offered with a range of thickness options from thin (3.00 mm) to ultrathin (30 μm) that are matched to typical pulse durations and spot sizes, listed in the tables below. When there is not a perfect match between any crystal thickness option and an application's laser pulse parameters, it is recommended that a crystal whose thickness is thinner, instead of thicker, than optimal be chosen. See the Specs tab for complete specifications for the nonlinear crystals listed below.

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 fundamental beam for Type-I critical phase matching (see Alignment for Optimal SHG below). Under phase matched conditions, the efficiency of the SHG process is improved, enabling the intensity of the SHG light to increase exponentially with propagation distance through the crystal. Phase matching in combination with suitable excitation intensities (10 - 100 GW/cm2) typically provides 10 - 50% conversion efficiencies.

To separate out the second harmonic from the fundamental of the output light, we recommend using a harmonic beamsplitter, as seen in the image above.

NLC06 Crystal in an RSP1 Rotation Mount on an RP01 Rotation Stage
Click to Enlarge
View Imperial Product List
Item #QtyDescription
NLC061Ø1" Mounted β-BBO Crystal, 2.00 mm Thick, θ = 23.3°, 900 - 1300 nm Fund., 450 - 650 nm SHG
RSP11Rotation Mount for Ø1" (25.4 mm) Optics, 8-32 Tap
RP011Ø2" Manual Rotation Stage
TR21Ø1/2" Optical Post, SS, 8-32 Setscrew, 1/4"-20 Tap, L = 2"
UPH21Ø1/2" Universal Post Holder, Spring Loaded Locking Thumbscrew, L = 2"
View Metric Product List
Item #QtyDescription
NLC061Ø1" Mounted β-BBO Crystal, 2.00 mm Thick, θ = 23.3°, 900 - 1300 nm Fund., 450 - 650 nm SHG
RSP1/M1Rotation Mount for Ø1" (25.4 mm) Optics, M4 Tap
RP01/M1Ø2" Manual Rotation Stage, Metric
TR50/M1Ø12.7 mm Optical Post, SS, M4 Setscrew, M6 Tap, L = 50 mm
UPH50/M1Ø12.7 mm Universal Post Holder, Spring-Loaded Locking Thumbscrew, L = 50 mm

NLC06 Crystal in an RSP1 Rotation Mount on an RP01 Rotation Stage

Alignment for Optimal SHG
To optimize the SHG process in β-BBO, Type-I phase matching can be achieved by aligning the polarization of the fundamental input light parallel to one of the crystal's principal ordinary axes, and then adjusting the angle between the optic axis and propagation direction so that both the fundamental and second harmonic light experience the same index of refraction (see the SHG Tutorial tab for a description of this process). For each of the crystals below, the angle between the optic axis and the normal to the crystal surface, θ, was chosen so that phase matching would be optimized for normally incident light at the Fundamental Wavelength, AOI = 0° specification listed in the tables below. For information on how the optimal angle for phase matching can be tuned for different fundamental wavelengths, see the Specs tab.

The front of each crystal’s housing is engraved with the polarization orientations for the fundamental input light (marked 1ω) and resulting orthogonally polarized second harmonic light (marked 2ω). A line across the middle of the housing indicates the axis around which the crystal can be rotated in order to adjust the angle between the fundamental beam’s propagation direction and the crystal’s optic axis.

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. The RSP1(/M) rotation mount facilitates aligning the crystal to the polarization direction of the fundamental-wavelength incident light. Additionally, 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 vertically polarized fundamental input beam, and the output second harmonic light will be horizontally polarized.

Usage, Handling, and Care
When handling the crystals, use care and always wear gloves. These crystals scratch easily, and the material is hygroscopic. Protect the crystals from excess moisture such as high humidity environments. If needed, we recommend 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 # NLC01 NLC02 NLC03 NLC08 NLC09 NLC04 NLC05 NLC06 NLC07
Crystal Thickness 0.15 mm 0.30 mm 0.60 mm 30 μm 75 μm 0.50 mm 1.00 mm 2.00 mm 3.00 mm
Crystal Thickness Tolerance ±0.02 mm ±0.05 mm +0 μm / -5 μm +0 μm / -11 μm ±0.05 mm
Angle of Optic Axis (θ)a 30.5° 29.2° 23.3° 19.8°
Tuning Angle vs. Wavelength Icon
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Optic Axis Angle (θ)a Tolerance ±0.5°
Fundamental Wavelength (1ω) AOI = 0° 770 nm 800 nm 1030 nm 1550 nm
AOI Tuned 680 - 900 nm 700 - 1200 nm 900 - 1300 nm 1300 - 1700 nm
SHG Wavelength (2ω) AOI = 0° 385 nm 400 nm 515 nm 775 nm
AOI Tuned 340 - 450 nm 350 - 600 nm 450 - 650 nm 650 - 850 nm
Minimum Recommended Focal Spot Size (1/e2 Diameter)b 25 µm 50 µm 100 µm 6 µm 12 µm 70 µm 140 µm 280 µm 360 µm
Circularity vs. Fundamental Mode Field Diameter (MFD)c Icon
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Minimum Recommended Pulse Duration (FWHM)b 30 fs 60 fs 120 fs 5.5 fs 14 fs 50 fs 100 fs 200 fs 15 fs
Minimum Fundamental Pulse Duration vs.
Fundamental Wavelength
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Phase Matching Bandwidth (FWHM)b 34 nm 17 nm 8 nm 165 nm 65 nm 30 nm 15 nm 7 nm 97 nm
Phase Matching Bandwidth vs.
Fundamental Wavelength
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Aperture Ø5.0 mm
Clear Aperture >80% of Diameter
Mount Diameter 1" (25.4 mm)
AR Coating Range 340 - 450 nm and 680 - 900 nm 650 - 1300 nm 450 - 650 nm and 900 - 1300 nm 650 - 850 nm and
1300 - 1700 nm
Reflectance Over Coating Range (Avg.) <4% at 0° AOI <1.25% at 0° AOI, Single-Layer AR
Coating on One Face Only
<3% at 0° AOI <4% at 0° AOI, Single-Layer AR
Coating on Both Faces
AR Coating Curve Icon
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Substrate N/A UV Fused Silica: Thickness = 2.5 mm,
Wedge Angle = 30 arcmin
N/A
Laser Induced Damage Thresholdd 0.5 J/cm2 (800 nm, 98 fs FWHM,
S-Pol, 104 Pulses)
0.8 J/cm2 (800 nm, 100 fs FWHM,
S-Pol, 104 Pulses)
0.3 J/cm2 (1030 nm, 190 fs FWHM,
S-Pol, 105 Pulses)
0.6 J/cm2 (1550 nm, 52 fs FWHM,
S-Pol, 104 Pulses)
Surface Quality 20-10 Scratch-Dig
Transmitted Wavefront Error λ/3 @ 632.8 nm Over Clear Aperture
  • Angle Between Crystal's Surface Normal and Optic Axis
  • Assumes incident light with fundamental wavelength 800 nm (Item #s NLC01, NLC02, NLC03, NLC08, and NLC09), 1030 nm (Item #s NLC04, NLC05, and NLC06), or 1550 nm (Item # NLC07).
  • The SHG output beam becomes increasingly elliptical below a certain input fundamental spot size.
  • For ultrafast optics, the laser induced damage threshold (LIDT) is defined as the fluence (per pulse) that produces visible damage after a given number of pulses. LIDT values are not guaranteed in the ultrashort pulse regime. As such, they are provided as a service to customers.
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
Nonlinear Refractive Index (Kerr Index)a 4.9 x 10−20 m2/W @ 1032 nm
Sellmeier Coefficientsb Ordinary Ray Sellmeier b-BBO n_o
Extraordinary Ray Sellmeier b-BBO n_e
Thermal Conductivity 1.2 W / m ⋅ K (⊥ C)
1.6 W / m ⋅ K (|| C)
Mohs Hardness 4.5 Mohs
Density 3.85 g/cm3
  • M. Bache, H. Guo, B. Zhou, and X. Zeng, "The anisotropic Kerr nonlinear refractive index of the beta-barium borate (β-BaB2O4) nonlinear crystal," Optical Materials Express,& 3(3), 357-382 (2013).
  • G. Tamošauskas, G. Beresnevicius, D. Gadonas, and A. Dubietis, "Transmittance and phase matching of BBO crystal in the 3 − 5 μm range and its application for the characterization of mid-infrared laser pulses," Optical Materials Express, 8(6), 1410-1418 (2018).

Second Harmonic Generation and Phase Matching

Optimizing the intensity and beam quality of the second harmonic light provided by these β-BBO crystals requires choosing the crystal thickness appropriate to the duration of the input laser pulses, determining a focal spot size that balances the positive and negative effects of the focal region, and optimizing the phase matching conditions. Succinct guidance on each of these topics is provided by the graphs available on the Specs tab. Additional information and background, which can be helpful for interpreting the graphed data as well as more effectively using the crystals to generate second harmonic light, is included in the expandable sections below.

Click on a question to expand the corresponding passage that provides an answer, and then click again to contract the section. Answers to questions lower in the list reference the discussions in preceding sections.

Damage Threshold Specificationsa
Item # Damage Threshold
NLC01 0.5 J/cm2 (800 nm, 98 fs FWHM, S-Pol, 104 Pulses)
NLC02
NLC03
NLC08 0.8 J/cm2 (800 nm, 100 fs FWHM, S-Pol, 104 Pulses)
NLC09
NLC04 0.3 J/cm2 (1030 nm, 190 fs FWHM, S-Pol, 105 Pulses)
NLC05
NLC06
NLC07 0.6 J/cm2 (1550 nm, 52 fs FWHM, S-Pol, 104 Pulses)
  • For ultrafast optics, the laser induced damage threshold (LIDT) is defined as the fluence (per pulse) that produces visible damage after a given number of pulses. LIDT values are not guaranteed in the ultrashort pulse regime. As such, they are provided as a service to customers.

Damage Threshold Data for Thorlabs' β-BBO Crystals

The specifications to the right are measured data for Thorlabs' β-BBO Crystals for Second Harmonic Generation.

 

Laser Induced Damage Threshold Tutorial

The following is a general overview of how laser induced damage thresholds are measured and how the values may be utilized in determining the appropriateness of an optic for a given application. When choosing optics, it is important to understand the Laser Induced Damage Threshold (LIDT) of the optics being used. The LIDT for an optic greatly depends on the type of laser you are using. Continuous wave (CW) lasers typically cause damage from thermal effects (absorption either in the coating or in the substrate). Pulsed lasers, on the other hand, often strip electrons from the lattice structure of an optic before causing thermal damage. Note that the guideline presented here assumes room temperature operation and optics in new condition (i.e., within scratch-dig spec, surface free of contamination, etc.). Because dust or other particles on the surface of an optic can cause damage at lower thresholds, we recommend keeping surfaces clean and free of debris. For more information on cleaning optics, please see our Optics Cleaning tutorial.

Testing Method

Thorlabs' LIDT testing is done in compliance with ISO/DIS 11254 and ISO 21254 specifications.

First, a low-power/energy beam is directed to the optic under test. The optic is exposed in 10 locations to this laser beam for 30 seconds (CW) or for a number of pulses (pulse repetition frequency specified). After exposure, the optic is examined by a microscope (~100X magnification) for any visible damage. The number of locations that are damaged at a particular power/energy level is recorded. Next, the power/energy is either increased or decreased and the optic is exposed at 10 new locations. This process is repeated until damage is observed. The damage threshold is then assigned to be the highest power/energy that the optic can withstand without causing damage. A histogram such as that below represents the testing of one BB1-E02 mirror.

LIDT metallic mirror
The photograph above is a protected aluminum-coated mirror after LIDT testing. In this particular test, it handled 0.43 J/cm2 (1064 nm, 10 ns pulse, 10 Hz, Ø1.000 mm) before damage.
LIDT BB1-E02
Example Test Data
Fluence # of Tested Locations Locations with Damage Locations Without Damage
1.50 J/cm2 10 0 10
1.75 J/cm2 10 0 10
2.00 J/cm2 10 0 10
2.25 J/cm2 10 1 9
3.00 J/cm2 10 1 9
5.00 J/cm2 10 9 1

According to the test, the damage threshold of the mirror was 2.00 J/cm2 (532 nm, 10 ns pulse, 10 Hz, Ø0.803 mm). Please keep in mind that these tests are performed on clean optics, as dirt and contamination can significantly lower the damage threshold of a component. While the test results are only representative of one coating run, Thorlabs specifies damage threshold values that account for coating variances.

Continuous Wave and Long-Pulse Lasers

When an optic is damaged by a continuous wave (CW) laser, it is usually due to the melting of the surface as a result of absorbing the laser's energy or damage to the optical coating (antireflection) [1]. Pulsed lasers with pulse lengths longer than 1 µs can be treated as CW lasers for LIDT discussions.

When pulse lengths are between 1 ns and 1 µs, laser-induced damage can occur either because of absorption or a dielectric breakdown (therefore, a user must check both CW and pulsed LIDT). Absorption is either due to an intrinsic property of the optic or due to surface irregularities; thus LIDT values are only valid for optics meeting or exceeding the surface quality specifications given by a manufacturer. While many optics can handle high power CW lasers, cemented (e.g., achromatic doublets) or highly absorptive (e.g., ND filters) optics tend to have lower CW damage thresholds. These lower thresholds are due to absorption or scattering in the cement or metal coating.

Linear Power Density Scaling

LIDT in linear power density vs. pulse length and spot size. For long pulses to CW, linear power density becomes a constant with spot size. This graph was obtained from [1].

Intensity Distribution

Pulsed lasers with high pulse repetition frequencies (PRF) may behave similarly to CW beams. Unfortunately, this is highly dependent on factors such as absorption and thermal diffusivity, so there is no reliable method for determining when a high PRF laser will damage an optic due to thermal effects. For beams with a high PRF both the average and peak powers must be compared to the equivalent CW power. Additionally, for highly transparent materials, there is little to no drop in the LIDT with increasing PRF.

In order to use the specified CW damage threshold of an optic, it is necessary to know the following:

  1. Wavelength of your laser
  2. Beam diameter of your beam (1/e2)
  3. Approximate intensity profile of your beam (e.g., Gaussian)
  4. Linear power density of your beam (total power divided by 1/e2 beam diameter)

Thorlabs expresses LIDT for CW lasers as a linear power density measured in W/cm. In this regime, the LIDT given as a linear power density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size, as demonstrated by the graph to the right. Average linear power density can be calculated using the equation below. 

The calculation above assumes a uniform beam intensity profile. You must now consider hotspots in the beam or other non-uniform intensity profiles and roughly calculate a maximum power density. For reference, a Gaussian beam typically has a maximum power density that is twice that of the uniform beam (see lower right).

Now compare the maximum power density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately. A good rule of thumb is that the damage threshold has a linear relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 10 W/cm at 1310 nm scales to 5 W/cm at 655 nm):

CW Wavelength Scaling

While this rule of thumb provides a general trend, it is not a quantitative analysis of LIDT vs wavelength. In CW applications, for instance, damage scales more strongly with absorption in the coating and substrate, which does not necessarily scale well with wavelength. While the above procedure provides a good rule of thumb for LIDT values, please contact Tech Support if your wavelength is different from the specified LIDT wavelength. If your power density is less than the adjusted LIDT of the optic, then the optic should work for your application. 

Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. The damage analysis will be carried out on a similar optic (customer's optic will not be damaged). Testing may result in additional costs or lead times. Contact Tech Support for more information.

Pulsed Lasers

As previously stated, pulsed lasers typically induce a different type of damage to the optic than CW lasers. Pulsed lasers often do not heat the optic enough to damage it; instead, pulsed lasers produce strong electric fields capable of inducing dielectric breakdown in the material. Unfortunately, it can be very difficult to compare the LIDT specification of an optic to your laser. There are multiple regimes in which a pulsed laser can damage an optic and this is based on the laser's pulse length. The highlighted columns in the table below outline the relevant pulse lengths for our specified LIDT values.

Pulses shorter than 10-9 s cannot be compared to our specified LIDT values with much reliability. In this ultra-short-pulse regime various mechanics, such as multiphoton-avalanche ionization, take over as the predominate damage mechanism [2]. In contrast, pulses between 10-7 s and 10-4 s may cause damage to an optic either because of dielectric breakdown or thermal effects. This means that both CW and pulsed damage thresholds must be compared to the laser beam to determine whether the optic is suitable for your application.

Pulse Duration t < 10-9 s 10-9 < t < 10-7 s 10-7 < t < 10-4 s t > 10-4 s
Damage Mechanism Avalanche Ionization Dielectric Breakdown Dielectric Breakdown or Thermal Thermal
Relevant Damage Specification No Comparison (See Above) Pulsed Pulsed and CW CW

When comparing an LIDT specified for a pulsed laser to your laser, it is essential to know the following:

Energy Density Scaling

LIDT in energy density vs. pulse length and spot size. For short pulses, energy density becomes a constant with spot size. This graph was obtained from [1].

  1. Wavelength of your laser
  2. Energy density of your beam (total energy divided by 1/e2 area)
  3. Pulse length of your laser
  4. Pulse repetition frequency (prf) of your laser
  5. Beam diameter of your laser (1/e2 )
  6. Approximate intensity profile of your beam (e.g., Gaussian)

The energy density of your beam should be calculated in terms of J/cm2. The graph to the right shows why expressing the LIDT as an energy density provides the best metric for short pulse sources. In this regime, the LIDT given as an energy density can be applied to any beam diameter; one does not need to compute an adjusted LIDT to adjust for changes in spot size. This calculation assumes a uniform beam intensity profile. You must now adjust this energy density to account for hotspots or other nonuniform intensity profiles and roughly calculate a maximum energy density. For reference a Gaussian beam typically has a maximum energy density that is twice that of the 1/e2 beam.

Now compare the maximum energy density to that which is specified as the LIDT for the optic. If the optic was tested at a wavelength other than your operating wavelength, the damage threshold must be scaled appropriately [3]. A good rule of thumb is that the damage threshold has an inverse square root relationship with wavelength such that as you move to shorter wavelengths, the damage threshold decreases (i.e., a LIDT of 1 J/cm2 at 1064 nm scales to 0.7 J/cm2 at 532 nm):

Pulse Wavelength Scaling

You now have a wavelength-adjusted energy density, which you will use in the following step.

Beam diameter is also important to know when comparing damage thresholds. While the LIDT, when expressed in units of J/cm², scales independently of spot size; large beam sizes are more likely to illuminate a larger number of defects which can lead to greater variances in the LIDT [4]. For data presented here, a <1 mm beam size was used to measure the LIDT. For beams sizes greater than 5 mm, the LIDT (J/cm2) will not scale independently of beam diameter due to the larger size beam exposing more defects.

The pulse length must now be compensated for. The longer the pulse duration, the more energy the optic can handle. For pulse widths between 1 - 100 ns, an approximation is as follows:

Pulse Length Scaling

Use this formula to calculate the Adjusted LIDT for an optic based on your pulse length. If your maximum energy density is less than this adjusted LIDT maximum energy density, then the optic should be suitable for your application. Keep in mind that this calculation is only used for pulses between 10-9 s and 10-7 s. For pulses between 10-7 s and 10-4 s, the CW LIDT must also be checked before deeming the optic appropriate for your application.

Please note that we have a buffer built in between the specified damage thresholds online and the tests which we have done, which accommodates variation between batches. Upon request, we can provide individual test information and a testing certificate. Contact Tech Support for more information.


[1] R. M. Wood, Optics and Laser Tech. 29, 517 (1998).
[2] Roger M. Wood, Laser-Induced Damage of Optical Materials (Institute of Physics Publishing, Philadelphia, PA, 2003).
[3] C. W. Carr et al., Phys. Rev. Lett. 91, 127402 (2003).
[4] N. Bloembergen, Appl. Opt. 12, 661 (1973).

In order to illustrate the process of determining whether a given laser system will damage an optic, a number of example calculations of laser induced damage threshold are given below. For assistance with performing similar calculations, we provide a spreadsheet calculator that can be downloaded by clicking the button to the right. To use the calculator, enter the specified LIDT value of the optic under consideration and the relevant parameters of your laser system in the green boxes. The spreadsheet will then calculate a linear power density for CW and pulsed systems, as well as an energy density value for pulsed systems. These values are used to calculate adjusted, scaled LIDT values for the optics based on accepted scaling laws. This calculator assumes a Gaussian beam profile, so a correction factor must be introduced for other beam shapes (uniform, etc.). The LIDT scaling laws are determined from empirical relationships; their accuracy is not guaranteed. Remember that absorption by optics or coatings can significantly reduce LIDT in some spectral regions. These LIDT values are not valid for ultrashort pulses less than one nanosecond in duration.

Intensity Distribution
A Gaussian beam profile has about twice the maximum intensity of a uniform beam profile.

CW Laser Example
Suppose that a CW laser system at 1319 nm produces a 0.5 W Gaussian beam that has a 1/e2 diameter of 10 mm. A naive calculation of the average linear power density of this beam would yield a value of 0.5 W/cm, given by the total power divided by the beam diameter:

CW Wavelength Scaling

However, the maximum power density of a Gaussian beam is about twice the maximum power density of a uniform beam, as shown in the graph to the right. Therefore, a more accurate determination of the maximum linear power density of the system is 1 W/cm.

An AC127-030-C achromatic doublet lens has a specified CW LIDT of 350 W/cm, as tested at 1550 nm. CW damage threshold values typically scale directly with the wavelength of the laser source, so this yields an adjusted LIDT value:

CW Wavelength Scaling

The adjusted LIDT value of 350 W/cm x (1319 nm / 1550 nm) = 298 W/cm is significantly higher than the calculated maximum linear power density of the laser system, so it would be safe to use this doublet lens for this application.

Pulsed Nanosecond Laser Example: Scaling for Different Pulse Durations
Suppose that a pulsed Nd:YAG laser system is frequency tripled to produce a 10 Hz output, consisting of 2 ns output pulses at 355 nm, each with 1 J of energy, in a Gaussian beam with a 1.9 cm beam diameter (1/e2). The average energy density of each pulse is found by dividing the pulse energy by the beam area:

Pulse Energy Density

As described above, the maximum energy density of a Gaussian beam is about twice the average energy density. So, the maximum energy density of this beam is ~0.7 J/cm2.

The energy density of the beam can be compared to the LIDT values of 1 J/cm2 and 3.5 J/cm2 for a BB1-E01 broadband dielectric mirror and an NB1-K08 Nd:YAG laser line mirror, respectively. Both of these LIDT values, while measured at 355 nm, were determined with a 10 ns pulsed laser at 10 Hz. Therefore, an adjustment must be applied for the shorter pulse duration of the system under consideration. As described on the previous tab, LIDT values in the nanosecond pulse regime scale with the square root of the laser pulse duration:

Pulse Length Scaling

This adjustment factor results in LIDT values of 0.45 J/cm2 for the BB1-E01 broadband mirror and 1.6 J/cm2 for the Nd:YAG laser line mirror, which are to be compared with the 0.7 J/cm2 maximum energy density of the beam. While the broadband mirror would likely be damaged by the laser, the more specialized laser line mirror is appropriate for use with this system.

Pulsed Nanosecond Laser Example: Scaling for Different Wavelengths
Suppose that a pulsed laser system emits 10 ns pulses at 2.5 Hz, each with 100 mJ of energy at 1064 nm in a 16 mm diameter beam (1/e2) that must be attenuated with a neutral density filter. For a Gaussian output, these specifications result in a maximum energy density of 0.1 J/cm2. The damage threshold of an NDUV10A Ø25 mm, OD 1.0, reflective neutral density filter is 0.05 J/cm2 for 10 ns pulses at 355 nm, while the damage threshold of the similar NE10A absorptive filter is 10 J/cm2 for 10 ns pulses at 532 nm. As described on the previous tab, the LIDT value of an optic scales with the square root of the wavelength in the nanosecond pulse regime:

Pulse Wavelength Scaling

This scaling gives adjusted LIDT values of 0.08 J/cm2 for the reflective filter and 14 J/cm2 for the absorptive filter. In this case, the absorptive filter is the best choice in order to avoid optical damage.

Pulsed Microsecond Laser Example
Consider a laser system that produces 1 µs pulses, each containing 150 µJ of energy at a repetition rate of 50 kHz, resulting in a relatively high duty cycle of 5%. This system falls somewhere between the regimes of CW and pulsed laser induced damage, and could potentially damage an optic by mechanisms associated with either regime. As a result, both CW and pulsed LIDT values must be compared to the properties of the laser system to ensure safe operation.

If this relatively long-pulse laser emits a Gaussian 12.7 mm diameter beam (1/e2) at 980 nm, then the resulting output has a linear power density of 5.9 W/cm and an energy density of 1.2 x 10-4 J/cm2 per pulse. This can be compared to the LIDT values for a WPQ10E-980 polymer zero-order quarter-wave plate, which are 5 W/cm for CW radiation at 810 nm and 5 J/cm2 for a 10 ns pulse at 810 nm. As before, the CW LIDT of the optic scales linearly with the laser wavelength, resulting in an adjusted CW value of 6 W/cm at 980 nm. On the other hand, the pulsed LIDT scales with the square root of the laser wavelength and the square root of the pulse duration, resulting in an adjusted value of 55 J/cm2 for a 1 µs pulse at 980 nm. The pulsed LIDT of the optic is significantly greater than the energy density of the laser pulse, so individual pulses will not damage the wave plate. However, the large average linear power density of the laser system may cause thermal damage to the optic, much like a high-power CW beam.


Posted Comments:
Emek Durmusoglu  (posted 2024-01-24 16:38:26.327)
Dear Thorlabs Technical Support, We have a Coherent VITARA-STi:S femtosecond laser (https://www.coherent.com/lasers/oscillators/vitara). The laser generates a beam at 800 nm and we want to use second-harmonic at 400 nm. Could you help us with the selection of the right BBO crystal for this purpose? Thank you. Best Regards, Emek Durmusoglu
jpolaris  (posted 2024-01-30 04:27:29.0)
Thank you for contacting Thorlabs. Given the < 20 fs pulse width that is specified for the Coherent laser that you have linked, you would be limited to either NLC08 or NLC09 from our catalog because NLC07 is not designed for 800 nm sources. It appears that both NLC08 and NLC09 have minimum recommended pulse widths that are less than the 20 fs pulse width of your laser. However, since conversion efficiency increases exponentially with crystal thickness, NLC09 is likely to give you the highest SHG intensity. I highly recommend that you verify that the specified "< 20 fs" pulse width is not actually lower than the 14 fs minimum recommended pulse width of NLC09.
runze liang  (posted 2023-08-01 12:36:10.393)
In the second harmonic generation tutorial, when explaining the relationship between refractive index and polarization direction, the discrete Angle between D and E is not considered, and D is perpendicular to K instead of E, is there a problem?
jpolaris  (posted 2023-08-08 06:58:31.0)
You are correct that the electric displacement vector (D) is orthogonal to the k-vector. The angle between the electric field vector (E) and the electric displacement vector (D) that you are referring to is explained by Poynting vector walk-off during second harmonic generation (also referred to as spatial walk-off). We can make a note clarifying this point. Thank you for your feedback!
YIHAUN SHI  (posted 2023-07-16 17:43:14.99)
请问你们NLC01-03这三款产品中,3dB转换光谱带宽最宽的是哪一款?3dB转换光谱带宽的范围是从哪个波长到哪个波长?谢谢
jpolaris  (posted 2023-07-21 02:53:49.0)
English Translation: Between NLC01, NLC02, and NLC03, which one has the widest 3 dB conversion spectral bandwidth? What is the range of its 3 dB conversion spectral bandwidth? Thank you for contacting Thorlabs. The NLC01 will have the broader phase matching bandwidth. At 800 nm, the phase matched SHG bandwidth is 33 nm FWHM, which equates to a Gaussian pulse 30 fs in duration. If instead, it is a series of pulses over a wide range of wavelengths with > 30 fs durations, then NLC01 will work well. The 33 nm figure assumes a fixed angle between the crystal and input laser, i.e., for a particular pulse. Our technical support team local to your region will reach out to you directly to discuss this further.
Benjamin Soloway  (posted 2023-05-31 22:15:14.65)
Hi, I was wondering if it's possible for you to produce a BBO crystal with a custom coating at 532nm fundamental and 266nm second harmonic generation. Best, Ben
jpolaris  (posted 2023-06-02 01:47:43.0)
Hello, thank you for contacting Thorlabs. The wavelength ranges of the antireflective coatings on these β-BBO crystals align with the respective wavelength bands that these crystals are optimized for. Requests for customizations can be made by reaching out to us at techsupport@thorlabs.com
YIHAUN SHI  (posted 2023-05-25 18:00:25.59)
请问你们NLC07这款晶体的转换带宽为多大?即在固定的输入角度下,最大的3db转换带宽
jpolaris  (posted 2023-05-30 04:44:13.0)
Hello, thank you for contacting Thorlabs. The 3 dB conversion bandwidth for NLC07 is 185 nm, with a center-wavelength of 1520 nm.

BBO Crystals, 680 - 900 nm (Fundamental) and 340 - 450 nm (SHG)

Key Specifications for SHG Applicationsa
Item # NLC01 NLC02 NLC03
Crystal Thickness 0.15 mm 0.30 mm 0.60 mm
Angle of Optic Axis (θ)b 30.5°
AR Coating Rangec 340 - 450 nm and 680 - 900 nm
Reflectance Over Coating Range (Avg.) <4% at 0° AOI
Fundamental Wavelength
(1ω)
AOI = 0° 770 nm
AOI Tunedc 680 - 900 nm
SHG Wavelength
(2ω)
AOI = 0° 385 nm
AOI Tuned 340 - 450 nm
Minimum Recommended Focal Spot Size
(1/e2 Diameter)c,d
25 µm 50 µm 100 µm
Minimum Recommended Pulse Duration (FWHM)c,d 30 fs 60 fs 120 fs
Phase Matching Bandwidth (FWHM)c,d 34 nm 17 nm 8 nm
  • See the Specs tab for complete specifications.
  • Angle Between Crystal's Surface Normal and Optic Axis
  • See the Specs tab for performance graphs.
  • Assumes incident light with fundamental wavelength 800 nm.
  • Mounted Crystal with Antireflection (AR) Coating for 340 - 450 nm and 680 - 900 nm
  • Suitable for Ti:Sapphire Lasers

These β-BBO crystals are designed to produce SHG emission from 340 to 450 nm from an input beam with a center wavelength in the range of 680 to 900 nm. They are available with thicknesses of 0.15, 0.30, or 0.60 mm and feature an AR coating to reduce surface reflections over the fundamental and second harmonic wavelength ranges. These mounted crystals can be used to frequency double the output of Ti:sapphire lasers, such as our Tiberius laser.

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NLC01 Support Documentation
NLC01Ø1" Mounted β-BBO Crystal, 0.15 mm Thick, θ = 30.5°, 680 - 900 nm Fund., 340 - 450 nm SHG
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NLC02 Support Documentation
NLC02Ø1" Mounted β-BBO Crystal, 0.30 mm Thick, θ = 30.5°, 680 - 900 nm Fund., 340 - 450 nm SHG
$561.00
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NLC03 Support Documentation
NLC03Ø1" Mounted β-BBO Crystal, 0.60 mm Thick, θ = 30.5°, 680 - 900 nm Fund., 340 - 450 nm SHG
$561.00
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Ultrathin BBO Crystals, 700 - 1200 nm (Fundamental) and 350 - 600 nm (SHG)

Key Specifications for SHG Applicationsa
Item # NLC08 NLC09
Crystal Thickness 30 μm 75 μm
Angle of Optic Axis (θ)b 29.2°
AR Coating Rangec 650 - 1300 nm
Reflectance Over Coating Range (Avg.) <1.25% at 0° AOI,
Single-Layer Coating,
One Side Only
Fundamental Wavelength
(1ω)
AOI = 0° 800 nm
AOI Tunedc 700 - 1200 nm
SHG Wavelength
(2ω)
AOI = 0° 400 nm
AOI Tuned 350 - 600 nm
Minimum Recommended Focal Spot Size (1/e2 Diameter)c,d 6 µm 12 µm
Minimum Recommended Pulse Duration (FWHM)c,d 5.5 fs 14 fs
Phase Matching Bandwidth (FWHM)c,d 165 nm 65 nm
Substrate UV Fused Silica:
Thickness = 2.5 mm,
Wedge Angle = 30 arcmin
  • See the Specs tab for complete specifications.
  • Angle Between Crystal's Surface Normal and Optic Axis
  • See the Specs tab for performance graphs.
  • Assumes incident light with fundamental wavelength 800 nm.

These ultrathin β-BBO crystals are designed to produce broad bandwidth SHG emission from 350 to 600 nm from an input beam with a center wavelength in the range of 700 to 1200 nm. They are available with thicknesses of either 30 or 75 μm and are bonded to a 2.5 mm thick UV fused silica (UVFS) substrate via epoxy-free optical contacting. The entrance crystal face features a single-layer AR coating to reduce surface reflections over the fundamental wavelength range only. The subsequent interface (βBBO to UVFS) and exit face (UVFS to air) are un-coated. Due to their large bandwidth, these mounted crystals can be used to frequency double the output of spectrally broadened ytterbium lasers, broadband optical parametric amplifier systems, few-cycle lasers, or nearly octave spanning Ti:sapphire lasers, such as our Octavius laser.

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NLC08 Support Documentation
NLC08Ø1" Mounted β-BBO Crystal, 30 μm Thick, θ = 29.2°, 700 - 1200 nm Fund., 350 - 600 nm SHG
$816.00
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NLC09 Support Documentation
NLC09Ø1" Mounted β-BBO Crystal, 75 μm Thick, θ = 29.2°, 700 - 1200 nm Fund., 350 - 600 nm SHG
$765.00
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BBO Crystals, 900 - 1300 nm (Fundamental) and 450 - 650 nm (SHG)

Key Specifications for SHG Applicationsa
Item # NLC04 NLC05 NLC06
Crystal Thickness 0.50 mm 1.00 mm 2.00 mm
Angle of Optic Axis (θ)b 23.3°
AR Coating Rangec 450 - 650 nm and 900 - 1300 nm
Reflectance Over Coating Range (Avg.) <3% at 0° AOI
Fundamental Wavelength
(1ω)
AOI = 0° 1030 nm
AOI Tunedc 900 - 1300 nm
SHG Wavelength
(2ω)
AOI = 0° 515 nm
AOI Tuned 450 - 650 nm
Minimum Recommended Focal Spot Size
(1/e2 Diameter)c,d
70 µm 140 µm 280 µm
Minimum Recommended Pulse Duration (FWHM)c,d 50 fs 100 fs 200 fs
Phase Matching Bandwidth (FWHM)c,d 30 nm 15 nm 7 nm
  • See the Specs tab for complete specifications.
  • Angle Between Crystal's Surface Normal and Optic Axis
  • See the Specs tab for performance graphs.
  • Assumes incident light with fundamental wavelength of 1030 nm.
  • Mounted Crystal with Antireflection (AR) Coating for 450 - 650 nm and 900 - 1300 nm
  • Suitable for Ytterbium (Yb) Lasers

These β-BBO crystals are designed to produce SHG emission from 450 to 650 nm from an input beam with a center wavelength in the range of 900 to 1300 nm. They are available with thicknesses of 0.50, 1.00, or 2.00 mm and feature an AR coating to reduce surface reflections over the fundamental and second harmonic wavelength ranges. These mounted crystals can be used to frequency double the output of ytterbium lasers.

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NLC04 Support Documentation
NLC04Ø1" Mounted β-BBO Crystal, 0.50 mm Thick, θ = 23.3°, 900 - 1300 nm Fund., 450 - 650 nm SHG
$561.00
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NLC05 Support Documentation
NLC05Ø1" Mounted β-BBO Crystal, 1.00 mm Thick, θ = 23.3°, 900 - 1300 nm Fund., 450 - 650 nm SHG
$561.00
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NLC06 Support Documentation
NLC06Ø1" Mounted β-BBO Crystal, 2.00 mm Thick, θ = 23.3°, 900 - 1300 nm Fund., 450 - 650 nm SHG
$561.00
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BBO Crystal, 1300 - 1700 nm (Fundamental) and 650 - 850 nm (SHG)

Key Specifications for SHG Applicationsa
Item # NLC07
Crystal Thickness 3.00 mm
Angle of Optic Axis (θ)b 19.8°
AR Coating Rangec 650 - 850 nm and 1300 - 1700 nm,
Single-Layer Coating, Both Faces
Reflectance Over Coating Range (Avg.) <4% at 0° AOI
Fundamental Wavelength
(1ω)
AOI = 0° 1550 nm
AOI Tunedc 1300 - 1700 nm
SHG Wavelength
(2ω)
AOI = 0° 775 nm
AOI Tuned 650 - 850 nm
Minimum Recommended Focal Spot Size
(1/e2 Diameter)c,d
360 µm
Minimum Recommended Pulse Duration (FWHM)c,d 15 fs
Phase Matching Bandwidth (FWHM)c,d 97 nm
  • See the Specs tab for complete specifications.
  • Angle Between Crystal's Surface Normal and Optic Axis
  • See the Specs tab for performance graphs.
  • Assumes incident light with fundamental wavelength of 1550 nm.

This 3.00 mm thick β-BBO crystal is designed to produce SHG emission from 650 to 850 nm from an input beam with a center wavelength in the range of 1300 to 1700 nm. It features single-layer AR coatings to reduce surface reflections over the fundamental and second harmonic wavelength ranges. This mounted crystal can be used to frequency double the output of erbium lasers or an optical parametric amplifier.

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NLC07 Support Documentation
NLC07Ø1" Mounted β-BBO Crystal, 3.00 mm Thick, θ = 19.8°, 1300 - 1700 nm Fund., 650 - 850 nm SHG
$540.60
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