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Large-Beam Fiber Collimators


  • Long Effective Focal Length: 40 mm or 80 mm
  • FC/PC or FC/APC Connector
  • Three AR-Coating Wavelength Ranges Available

Application Idea

C40FC-A Collimator Mounted on a Ø1/2" Post Using an SM1RC Slip Ring

C80APC-A (Front View)

80 mm Focal Length, FC/APC Connector, and AR Coated for 400 - 650 nm

C40FC-B (Back View)

40 mm Focal Length, FC/PC Connector, and AR Coated for 650 - 1050 nm

C80APC-C (Back View)

80 mm Focal Length, FC/APC Connector, and AR Coated for 1050 - 1650 nm

Related Items


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Zoom Fiber Collimators with Lens Tubes
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The free-space end of the collimators has either external SM2 or SM1 threading for attaching Ø2" or Ø1" lens tubes, respectively.

Features

  • Ideal for Fiber-to-Free-Space Collimation or Coupling
  • Effective Focal Length (EFL): 40 mm or 80 mm
  • Three Broadband Antireflection Coatings Available (See the Coating Tab for Plots)
    • 400 nm - 650 nm: Rmax < 0.5%
    • 650 nm - 1050 nm: Rmax < 0.5%
    • 1050 nm - 1650 nm: Rmax < 0.5%
  • Closest Focusing Distance: 0.35 m (40 mm EFL) or 0.7 m (80 mm EFL)
  • Couple Free-Space Beams up to Ø42.5 mm
  • Near-Gaussian Output
  • Diffraction-Limited Wavefront Error: λ/8 (Typical, P-V at 633 nm with 0.14 NA Fiber)
  • Available with a 2.2 mm Wide Key FC/PC or FC/APC Connector (Dust Cap Included)
  • Ø1.2" or Ø2.2" Outer Diameter Provides Compatibility with Slip Rings and Tube Clamps
  • External SM1 or SM2 Threading for Compatibility with Ø1" or Ø2" Lens Tubes
  • Packages with an SMA Connector Are Offered as a Special; Contact Tech Support

Thorlabs' Large-Beam Fiber Collimators are designed with an effective focal length (EFL) of 40 mm or 80 mm over three different wavelength ranges and are available with FC/PC or FC/APC connectors. A four-element, air-spaced lens design produces a superior beam quality (M2 close to 1) and less wavefront error when compared to aspheric lens collimators. A red wheel adjusts the focus distance between infinity and the closest focusing distance; the wheel can be locked using the included 0.05" (1.3 mm) hex key. As a result, these collimators are very flexible; they can be used as free-space collimator or coupler. They may also be used over a long distance in pairs, which allows the free-space beam to be manipulated prior to entering the second collimator and may be useful in long-distance communications applications.

To minimize losses caused by surface reflections, all the lenses in the collimator feature a broadband AR coating on both sides (see the Coating tab for details). AR coatings for three different wavelength ranges are available: 400 - 650 nm, 650 - 1050 nm, or 1050 - 1650 nm. Please contact Tech Support for laser line (V-coating) AR coatings centered at a specific wavelength.

These collimation packages use 2.2 mm wide key connectors with tightly toleranced ceramic sleeves that provide excellent pointing repeatability, allowing the user to easily adjust the focus distance and replace the fiber without the need for large realignments. Please note that careful alignment is needed when mating a narrow key PM fiber with the collimator's wide key receptacle. Collimators with an SMA connector are available as a special; contact Tech Support for a quote. Other collimators are also available; for our complete line of collimation and coupling options, please see the Collimator Guide tab.

Mounting Options
Each collimator has a black-anodized outer Ø1.2" or Ø2.2" region, which matches the outer diameter of our Ø1" or Ø2" lens tubes, respectively. As a result, the collimators can be easily mounted to a post using slip rings or tube clamps. The free-space end of the 40 mm EFL and 80 mm EFL collimators feature external SM1 (1.035"-40) and SM2 (2.035"-40) threading, respectively. This makes it easy to integrate these collimators into our entire line of optomechanical components, such as 30 mm and 60 mm cage systems. The threaded ring at the end of the collimator does not rotate when turning the focus adjustment ring, allowing the user to adjust the focus without disturbing any attached optics (see the Performance tab for more information).

Converging or Diverging
Converging LightDiverging Light
Collimated
Collimated Light

Collimation

When collimating light, a shearing interferometer can be used to determine if a coherent beam of light is collimated. The interferometer is comprised of a wedged optical flat mounted at 45° and a diffuser plate with a ruled reference line down the middle.

The diffuser plate can then be used to view the interference fringes created by Fresnel reflections from the front and back surfaces of the optical flat (as shown in the images to the right). If the beam is collimated, the resulting fringe pattern will be parallel to the ruled reference line. In addition to the degree of collimation, the fringes will also be sensitive to spherical aberration, coma, and astigmatism.

  

Free-Space Coupling

When using these collimators as a free-space coupler, precise alignment is needed for good coupling efficiency. In general, six movement degrees of freedom are recommended, such as pairing a kinematic mount with an XYZ translation stage. For example, the 40 mm collimators can be mounted with a KM100T, KC1-T (KC1-T/M), or KS1T kinematic mount and an MT3 (MT3/M) translation stage. The 80 mm collimators can be mounted using the KM200T, KC2-T (KC2-T/M), or KS2T kinematic mounts with an MT3 (MT3/M) Translation Stage. The beam can be focused anywhere between the maximum waist distance (see the Divergence tab for details) and the closest focusing distance, enabling easy optimization of coupling efficiency. AR-coated single mode or polarization-maintaining patch cables can be used to further increase coupling efficiency and beam quality; these cables feature an AR coating on one connector end that improves return loss at the fiber-to-free-space interface when coupling.

  

Zoom Collimator Adjustments
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The focus wheel provides smooth adjustment of the focusing distance.

Adjustment

Thorlabs' large-beam fiber collimators provide a fixed 40 mm or 80 mm focal length while allowing the beam to be focused between the maximum waist distance (see the Divergence tab) and the closest focusing distance. This allows for simple optimization of coupling efficiency from free-space laser beam into a fiber. 

To adjust the focusing distance, rotate the red section of the housing as shown in the image to the right; this will alter the focal point of the beam. There is a setscrew on one end for locking the focus which can be adjusted using the included 0.05" (1.3 mm) hex key.

Longitudinal Chromatic Aberration
When used within the specified operating wavelength range, these large-beam fiber collimators are designed to introduce a minimal amount of longitudinal chromatic aberration, also known as chromatic focal shift. This occurs when the focal planes for different wavelengths of light are located at different distances from the same focusing optic.

The focal shift produced by these collimators when they are used as couplers is shown the graphs below. The theoretical deviation of the focal plane location from the nominal focal length is plotted over the operating wavelength range. The calculation was performed for each coating type at the available focal lengths (40 mm and 80 mm).

Longitudinal Chromatic Aberration
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Click Here for Theoretical Data
The chromatic focal shift for the 400 - 650 nm large-beam fiber collimators. The blue-shaded region indicates the specified operating wavelength range of the collimator.
Longitudinal Chromatic Aberration
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Click Here for Theoretical Data
The chromatic focal shift for the 650 - 1050 nm large-beam fiber collimators. The blue-shaded region indicates the specified operating wavelength range of the collimator.
Longitudinal Chromatic Aberration
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Click Here for Theoretical Data
The chromatic focal shift for the 1050 - 1650 nm large-beam fiber collimators. The blue-shaded region indicates the specified operating wavelength range of the collimator.

The graphs below illustrate the theoretical beam diameter as a function of propagation distance for certain SM-coupled laser wavelengths using our large-beam collimators and triplet collimators adjusted for the minimum divergence. These graphs are valid for all large-beam collimators when using single mode fibers and show that the large-beam collimators exhibit minimal divergence over a long distance from the collimator when compared to collimators with a shorter focal length.

Theoretical Approximation of the Divergence Angle

The divergence angle is easy to approximate theoretically using the formula below as long as the light emerging from the fiber has a Gaussian intensity profile. Consequently, the formula works well for single mode (SM) fibers, but will underestimate the divergence angle for multimode (MM) fibers since light emerging from an MM fiber has a non-Gaussian intensity profile.

The full divergence angle (in degrees) is given by:

Divergence Angle Equation

where MFD is the mode field diameter and f is the focal length of the collimator; both MFD and focal length must have the same units in this equation.

Example Calculation:

When the C40APC-A collimator is used with the P3-460B-FC-1 SM patch cable, MFD = 3.6 µm, f ≈ 40 mm, and λ = 543 nm, the divergence angle is:

θ ≈ (0.0036 mm / 40 mm) x (180 / 3.1416) ≈ 0.0051° or 0.089 mrad.

Theoretical Approximation of the Output Beam Diameter

The output beam diameter can be approximated from the equation below:

Output Beam Diameter Equation

where λ is the wavelength of light being used, MFD is the mode field diameter, and f is the focal length of the collimator.

Example Calculation:

When the C80FC-C collimator (f = 80 mm) is used with the P1-SMF28E-FC-1 patch cable (MFD = 10.5 µm) at 1550 nm, the output beam diameter is:

d = 4 x 1550 nm x [80 mm / (3.1416 · 10.5 µm)] = 15.0 mm

Theoretical Approximation of the Maximum Waist Distance

The maximum waist distance, which is the furthest distance from the lens, may be approximated by:

Max Waist Distance Calculation

where f is the focal length of the collimator, λ is the wavelength of light used, and MFD is the mode field diameter.

Example Calculation:

When the C40FC-A collimator is used with the P3-460B-FC-1 SM patch cable, MFD = 3.6 µm, f = 40.0 mm, and λ = 543 nm, then the maximum waist distance is:

40 mm + (2 x (40 mm)2 x (543 nm) / (3.1416) x (3.6 µm)2) = 42.7 m.

The graphs below show the reflectance with respect to the wavelength of the AR coatings used on the 8 lens surfaces in our large-beam fiber collimators (two surfaces per lens). The blue shaded region indicates the wavelength range specified for each coating. The table below details which AR coating is used with each collimator.

Antireflection Coatings
Item #  Wavelength Range Reflectance (Per Surface)a
C40FC-A 400 - 650 nmb Rmax < 0.5%
C40APC-A
C80FC-A
C80APC-A
C40FC-A 650 - 1050 nm Rmax < 0.5%
C40APC-A
C80FC-A
C80APC-A
C40FC-A 1050 - 1650 nm Rmax < 0.5%
C40APC-A
C80FC-A
C80APC-A
  • Each collimator has 8 coated surfaces.
  • Please note that transmission below 400 nm is significantly reduced, as seen in the Zemax black box files.
Damage Threshold Specifications
Item # Suffix AR Coating Damage Threshold
-A 400 - 650 nm 3 J/cm2 (532 nm, 10 Hz, 10 ns, Ø408 μm)
-B 650 - 1050 nm 7.5 J/cm2 (810 nm, 10 Hz, 10 ns, Ø76.9 μm)
-C 1050 - 1650 nm 3 J/cm2 (1542 nm, 1 Hz, 10 ns, Ø268 μm)

Damage Threshold Data for Thorlabs' Large-Beam Fiber Collimators

The specifications to the right are measured data for Thorlabs' Large-Beam Fiber Collimators.

 

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.

Fiber Collimator Selection Guide

Click on the collimator type or photo to view more information about each type of collimator.

Type   Description
Fixed FC, APC, or SMA Fiber Collimators Fixed SMA Fiber Collimator These fiber collimation packages are pre-aligned to collimate light from an FC/PC-, FC/APC-, or SMA-terminated fiber. Each collimation package is factory aligned to provide diffraction-limited performance for wavelengths ranging from 405 nm to 4.55 µm. Although it is possible to use the collimator at detuned wavelengths, they will only perform optimally at the design wavelength due to chromatic aberration, which causes the effective focal length of the aspheric lens to have a wavelength dependence.
Air-Spaced Doublet, Large Beam Collimators Air-Spaced Doublet Fiber Collimator For large beam diameters (Ø5.3 - Ø8.5 mm), Thorlabs offers FC/APC, FC/PC, and SMA air-spaced doublet collimators. These collimation packages are pre-aligned at the factory to collimate a laser beam propagating from the tip of an FC or SMA-terminated fiber and provide diffraction-limited performance at the design wavelength.
Triplet Collimators Triplet Fiber Collimator Thorlabs' High Quality Triplet Fiber Collimation packages use air-spaced triplet lenses that offer superior beam quality performance when compared to aspheric lens collimators. The benefits of the low-aberration triplet design include an M2 term closer to 1 (Gaussian), less divergence, and less wavefront error.
Achromatic Collimators for Multimode Fiber Triplet Fiber Collimator Thorlabs' High-NA Achromatic Collimators pair a meniscus lens with an achromatic doublet for high performance across the visible spectrum with low spherical aberration. Designed for use with high-NA multimode fiber, these collimators are ideal for Optogenetics and Fiber Photometry applications.
Reflective Collimators Reflective Fiber Collimator Thorlabs' metallic-coated Reflective Collimators are based on a 90° off-axis parabolic mirror. Mirrors, unlike lenses, have a focal length that remains constant over a broad wavelength range. Due to this intrinsic property, a parabolic mirror collimator does not need to be adjusted to accommodate various wavelengths of light, making them ideal for use with polychromatic light. Our reflective collimators are ideal for single-mode fiber.
FiberPorts Fiberport Fiber Collimator These compact, ultra-stable FiberPort micropositioners provide an easy-to-use, stable platform for coupling light into and out of FC/PC, FC/APC, or SMA terminated optical fibers. It can be used with single mode, multimode, or PM fibers and can be mounted onto a post, stage, platform, or laser. The built-in aspheric or achromatic lens is available with five different AR coatings and has five degrees of alignment adjustment (3 translational and 2 pitch). The compact size and long-term alignment stability make the FiberPort an ideal solution for fiber coupling, collimation, or incorporation into OEM systems.
Adjustable Fiber Collimators Adjustable Fiber Collimator These collimators are designed to connect onto the end of an FC/PC or FC/APC connector and contain an AR-coated aspheric lens. The distance between the aspheric lens and the tip of the FC-terminated fiber can be adjusted to compensate for focal length changes or to recollimate the beam at the wavelength and distance of interest.
Large Beam Fiber Collimators large beam collimators Thorlabs' Large-Beam Fiber Collimators are designed with an effective focal length (EFL) of 40 mm or 80 mm over three different wavelength ranges and are available with FC/PC or FC/APC connectors. A four-element, air-spaced lens design produces a superior beam quality (M2 close to 1) and less wavefront error when compared to aspheric lens collimators. As a result, these collimators are very flexible; they can be used as free-space collimator or coupler. They may also be used over a long distance in pairs, which allows the free-space beam to be manipulated prior to entering the second collimator and may be useful in long-distance communications applications.
Zoom Fiber Collimators Zoom Fiber Collimator These collimators provide a variable focal length between 6 and 18 mm, while maintaining the collimation of the beam. As a result, the size of the beam can be changed without altering the collimation. This universal device saves time previously spent searching for the best suited fixed fiber collimator and has a very broad range of applications. They are offered with FC/PC, FC/APC, or SMA905 connectors with three different antireflection wavelength ranges to choose from.
Pigtailed Collimators Pigtailed Fiber Collimator Our pigtailed collimators come with one meter of either single mode or multimode fiber, have the fiber and AR-coated aspheric lens rigidly potted inside the stainless steel housing, and are collimated at one of six wavelengths: 532, 830, 1030, 1064, 1310, or 1550 nm. Although it is possible to use the collimator at any wavelength within the coating range, the coupling loss will increase as the wavelength is detuned from the design wavelength.
GRIN Fiber Collimators GRIN Fiber Collimator Thorlabs offers gradient index (GRIN) fiber collimators that are aligned at a variety of wavelengths from 630 to 1550 nm and have either FC terminated, APC terminated, or unterminated fibers. Our GRIN collimators feature a Ø1.8 mm clear aperture, are AR-coated to ensure low back reflection into the fiber, and are coupled to standard single mode or graded-index multimode fibers.
GRIN Lenses GRIN Lens These graded-index (GRIN) lenses are AR coated for applications at 630, 830, 1060, 1300, or 1560 nm that require light to propagate through one fiber, then through a free-space optical system, and finally back into another fiber. They are also useful for coupling light from laser diodes into fibers, coupling the output of a fiber into a detector, or collimating laser light. Our GRIN lenses are designed to be used with our Pigtailed Glass Ferrules and GRIN/Ferrule sleeves.

Posted Comments:
kevin.yyw  (posted 2018-11-22 03:02:10.983)
Dear Thorlabs team: For this item of focuser, can we change the connector for SMA905? We need it to do the fiber alingment, but we must use SMA905 connector, because our customer require select SMA905 connector fiber.
YLohia  (posted 2018-12-03 12:20:32.0)
Hello, thank you for contacting Thorlabs. Custom beam expanders can be requested through techsupport@thorlabs.com. I will reach out to you directly regarding the possibility of obtaining one of these.
rkharrison  (posted 2018-07-25 12:23:26.577)
Hi, Can you make one of these with SMA fiber coupling? Thanks, Rick
YLohia  (posted 2018-07-26 08:44:34.0)
Hi Rick, I have reached out to you directly to discuss the possibility of offering this.
user  (posted 2018-01-17 18:15:09.33)
divergence calculation is wrong. Should be 0.089 mrad.
tcampbell  (posted 2018-01-19 10:11:51.0)
Hello, thank you for contacting Thorlabs. Our calculation already shows the result of 0.089 mrad. Feel free to contact us at techsupport@thorlabs.com if you have further questions about our calculations.

Collimators for 400 - 650 nm

Item # EFLa Typical Collimated Beam
Diameter (Alignment Fiber)b
Closest Focus
Distance
Clear
Aperturec
Outer
Diameterd
Threading Connector Transmission AR Coating Fiber NA
(Max)e
C40FC-A 40 mm 7.5 mm (SM400 at 405 nm)
7.4 mm (SM450 at 543 nm)
7.4 mm (SM600 at 633 nm)
0.35 m Ø20.5 mm 1.2" External SM1
(1.035"-40)
2.2 mm FC/PC  93% at 405 nm
93% at 543 nm
93% at 633 nm
400 - 650 nm
Rmax < 0.5%
Per Surface
0.25
C40APC-A 2.2 mm FC/APC
C80FC-A 80 mm 15.2 mm (SM400 at 405 nm)
14.9 mm (SM450 at 543 nm)
15.0 mm (SM600 at 633 nm)
0.7 m Ø42.5 mm 2.2" External SM2
(2.035"-40)
2.2 mm FC/PC
C80APC-A 2.2 mm FC/APC
  • Effective Focal Length
  • The 1/e2 beam diameters given were measured for the specific single mode fibers listed and at the specified wavelengths.
  • Specifies the largest beam size that can enter or exit the collimator.
  • These collimators can be mounted using tube clamps and slip rings. Collimators with a 1.2" outer diameter can be used with the SM1RC, SM1RC/MSM1TCCP12, and SM2A21. Collimators with a 2.2" outer diameter can be used with the SM2RC, SM2RC/MSM2TC, and LCP09.
  • Specifies the maximum fiber NA that can be used when collimating light from a fiber.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
C40FC-A Support Documentation
C40FC-ALarge-Beam Fiber Collimator, f = 40 mm, FC/PC, ARC: 400 - 650 nm
$875.50
Today
C40APC-A Support Documentation
C40APC-ALarge-Beam Fiber Collimator, f = 40 mm, FC/APC, ARC: 400 - 650 nm
$875.50
5-8 Days
C80FC-A Support Documentation
C80FC-ALarge-Beam Fiber Collimator, f = 80 mm, FC/PC, ARC: 400 - 650 nm
$1,236.00
Today
C80APC-A Support Documentation
C80APC-ALarge-Beam Fiber Collimator, f = 80 mm, FC/APC, ARC: 400 - 650 nm
$1,236.00
Today

Collimators for 650 - 1050 nm

Item # EFLa Typical Collimated Beam
Diameter (Alignment Fiber)b
Closest Focus
Distance
Clear
Aperturec
Outer
Diameter
d
Threading Connector Transmission AR Coating Fiber NA
(Max)e
C40FC-B 40 mm 8.6 mm (780HP at 780 nm)
8.6 mm (SM980-5.8-125 at 980 nm)
0.35 m Ø20.5 mm 1.2" External SM1
(1.035"-40)
2.2 mm FC/PC  96% at 780 nm
95% at 980 nm
650 - 1050 nm
Rmax < 0.5%
Per Surface
0.25
C40APC-B 2.2 mm FC/APC
C80FC-B 80 mm 17.3 mm (780HP at 780 nm)
17.2 mm (SM980-5.8-125 at 980 nm)
0.7 m Ø42.5 mm 2.2" External SM2
(2.035"-40)
2.2 mm FC/PC
C80APC-B 2.2 mm FC/APC
  • Effective Focal Length
  • The 1/e2 beam diameters given were measured for the specific single mode fibers listed and at the specified wavelengths.
  • Specifies the largest beam size that can enter or exit the collimator.
  • These collimators can be mounted using tube clamps and slip rings. Collimators with a 1.2" outer diameter can be used with the SM1RC, SM1RC/MSM1TCCP12, and SM2A21. Collimators with a 2.2" outer diameter can be used with the SM2RC, SM2RC/MSM2TC, and LCP09.
  • Specifies the maximum fiber NA that can be used when collimating light from a fiber.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
C40FC-B Support Documentation
C40FC-BLarge-Beam Fiber Collimator, f = 40 mm, FC/PC, ARC: 650 - 1050 nm
$875.50
Today
C40APC-B Support Documentation
C40APC-BLarge-Beam Fiber Collimator, f = 40 mm, FC/APC, ARC: 650 - 1050 nm
$875.50
Today
C80FC-B Support Documentation
C80FC-BLarge-Beam Fiber Collimator, f = 80 mm, FC/PC, ARC: 650 - 1050 nm
$1,236.00
Today
C80APC-B Support Documentation
C80APC-BLarge-Beam Fiber Collimator, f = 80 mm, FC/APC, ARC: 650 - 1050 nm
$1,236.00
Today

Collimators for 1050 - 1650 nm

Item # EFLa Typical Collimated Beam
Diameter (Alignment Fiber)b
Closest Focus
Distance
Clear
Aperturec
Outer
Diameter
d
Threading Connector Transmission AR Coating Fiber NA (Max)e
C40FC-C 40 mm 8.7 mm (SM980-5.8-125 at 1064 nm)
7.2 mm (SMF-28-J9 at 1310 nm)
7.3 mm (SMF-28-J9 at 1550 nm)
0.35 m Ø20.5 mm 1.2" External SM1
(1.035"-40)
2.2 mm FC/PC  92% at 1064 nm
92% at 1310 nm
92% at 1550 nm
1050 - 1650 nm
Rmax < 0.5%
Per Surface
0.25
C40APC-C 2.2 mm FC/APC
C80FC-C 80 mm 17.5 mm (SM980-5.8-125 at 1064 nm)
14.5 mm (SMF-28-J9 at 1310 nm)
14.5 mm (SMF-28-J9 at 1550 nm)
0.7 m Ø42.5 mm 2.2" External SM2
(2.035"-40)
2.2 mm FC/PC
C80APC-C 2.2 mm FC/APC
  • Effective Focal Length
  • The 1/e2 beam diameters given were measured for the specific single mode fibers listed and at the specified wavelengths.
  • Specifies the largest beam size that can enter or exit the collimator.
  • These collimators can be mounted using tube clamps and slip rings. Collimators with a 1.2" outer diameter can be used with the SM1RC, SM1RC/MSM1TCCP12, and SM2A21. Collimators with a 2.2" outer diameter can be used with the SM2RC, SM2RC/MSM2TC, and LCP09.
  • Specifies the maximum fiber NA that can be used when collimating light from a fiber.
Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
C40FC-C Support Documentation
C40FC-CLarge-Beam Fiber Collimator, f = 40 mm, FC/PC, ARC: 1050 - 1650 nm
$875.50
Today
C40APC-C Support Documentation
C40APC-CLarge-Beam Fiber Collimator, f = 40 mm, FC/APC, ARC: 1050 - 1650 nm
$875.50
Today
C80FC-C Support Documentation
C80FC-CLarge-Beam Fiber Collimator, f = 80 mm, FC/PC, RC: 1050 - 1650 nm
$1,236.00
Today
C80APC-C Support Documentation
C80APC-CLarge-Beam Fiber Collimator, f = 80 mm, FC/APC, ARC: 1050 - 1650 nm
$1,236.00
Today
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