Laser Beam Profiler Accessories

Coherent LaserCam Attenuation Accessories

Laser-grade attenuation optics protect sensitive cameras from damage

Accessory, laser-grade attenuation optics are available for the Coherent LaserCam HR, BeamView and BeamMaster laser beam profilers to prevent damage to their delicate sensors. The optics thread directly to the C-mount adaptor fitted to the face-plate of each camera (optional on BeamMaster) to provide virtually distortion-free fixed or variable attenuation for beams up to 2kW/cm² or 50J/cm².

» Download Attenuator Datasheet

Why Attenuate?

CCD or CMOS camera sensors are too sensitive for direct viewing of most laser beams, unless you wish to regard them as consumables (unlikely!) For example, a typical CCD sensor saturates at a power density of only ~0.5 μW/cm² (at 633nm) or an energy density of ~9 nJ/cm² (at 1060nm). At about 1000 times the saturation irradiance, actual damage can occur to the camera sensor. If the camera has an electronic shutter, this can be used for some CW beam attenuation, but there is more flexibility in using optical attenuation accessories.

Flexible Attenuation Options

A LDFP low distortion face plate filter is supplied as standard with each camera. The LDFP is a laser-grade ND filter glass (attenuation of ~2,500:1 at 633nm) which is specified and polished for diagnostics use. It is mounted in a C-mount thread and provides sufficient attenuation of room light so that the camera can be used with the lights on. For operation below 400nm, the LDFP must be removed.

For higher levels of attenuation, Coherent offer precision accessory optics that possess the necessary flatness and wedge to avoid distortion of the beam under test. These simply screw into the C-mount fitting on each camera and offer attenuation at fixed or variable levels between zero and 400,000:1.

The BeamCube fixed attenuator modules (BCUBE and UV-BCUBE) provide fixed attenuation and beam pick-off for performing diagnostics on high power laser sources. These accessories utilise the front surface reflection from an uncoated laser mirror to sample between 2 and 10% of the incident radiation, depending upon the beam's polarisation state. Multiple BCUBEs can be coupled together for even higher fixed attenuation levels.

The VARM variable attenuator module is a triple-wheel filter holder that contains three filters per wheel. The VARM is adjustable in attenuation in 64 discrete steps giving approximately 16% reduction at each step from 400,000:1 down to 1:1. The VARM can be easily returned to exactly the same attenuation level as previously used.

The C-VARM and UV C-VARM continuously variable attenuator modules contain two wedge attenuators that are continuously variable and a step attenuator that will allow attenuation from 107:1 down to 3,000:1. The C-VARM and UV C-VARM can be finely adjusted to achieve both precise attenuation levels and maximum use of the camera’s dynamic range.

Configuring Attenuator Modules with your Profiler

BCUBE, UV-BCUBE, VARM, C-VARM, UV C-VARM each mate to the female C-mount thread on a camera using the male C-mount connection flange provided with each attenuator. All attenuators have a ¼-20 tapped hole for independent post or plate mounting. In addition, a set of three flanges and two extension barrels are available that allow you to join different attenuator modules together. The C-mount flanges have a female RMS microscope thread. This allows a microscope objective to be coupled to the attenuators and extension barrels in order to to create a flexible, close-up imaging system for the analysis of small or focused laser beams, fiber optics, laser diodes or LEDs.

Attenuation selection for cameras is an easy process. Attenuation is selected on the basis of power density in W/cm² or energy density in J/cm². The attenuation from the camera’s LDFP will allow an average power density of up to 1.2 mW/cm². Above that, choose either the VARM or the C-VARM for use at up to 1W/cm². In addition (or alternatively), use a BCUBE beamsplitter module to pick off between 5% and 20% of the beam (depending on polarisation and wavelength).

The illustration below shows how to configure the various attenuator modules with any Coherent camera-based profiler.

Possible CCD Camera Attenuation Configuration

Ordering Information

P/N	Description	Wavelength (nm)		Attenuation (times)		Aperture (mm)	Max. Power or Energy Density		Damage Threshold		Beam Offset
		Min	Max	From	To		(W/cm²)	(J/cm²)	(W/cm²)	(J/cm²)	(mm)
33-3328	VARM	380	2200	4x10⁵	1	19	1	0.1	5x10⁷	10	N/A
33-3336	C-VARM	380	2200	10⁷	3x10³	17	1	0.1	5x10⁷	10	N/A
33-6859	UV C-VARM	190	1100	10⁵	3x10²	17	1	0.008	-	0.008	N/A
1098403	BCUBE	380	2200	50	10	19	2x10⁹	50	2.5x10⁹	50	4.0
1098466	UV BCUBE	190	2200	50	10	19	2x10⁹	50	2.5x10⁹	50	4.0
1099426	Barrel Set*	-	-	-	-	-	-	-	-	-	-

* Barrel set comprises 2 connection barrels and 3 C-mount flanges

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