Laser 2000

Liquid Crystal Attenuators

LVA Series

Computer control of light intensity

The LVA offers real‐time, continuous control of light intensity. Our attenuator consists of an LC Variable Retarder (with attached compensator) operating between crossed linear polarisers.

With crossed polarisers, light transmission is maximized by applying the correct voltage to achieve half‐wave retardance from the LC cell. Half‐wave operation rotates the incoming polarisation direction by 90°, so that light is passed by the second polariser. Minimum transmission is obtained with the retarder operating at zero (or a whole number of) waves.

Transmission decreases as the applied AC voltage amplitude increases (half‐ to zero‐waves retardance). The relationship between transmittance T and retardance (in degrees) for crossed polariser configuration is given

by: T(Θ) = 1/2 [1 ‐ cos(Θ)] Tmax

where Tmax is the maximum transmittance
when retardance is exactly one‐half wave (or 180°).

A Liquid Crystal Variable Attenuator can be configured with high efficiency calcite or beamsplitting polarisers to maximize light transmittance and increase damage threshold. With a linearly polarised input beam and a calcite polariser, transmittance values exceed 90% at most wavelengths. Very high contrast ratios, in excess of 5000:1, can be achieved with custom double attenuators. In this design, two Liquid Crystal Variable Retarders are combined with three polarisers.

Custom devices for near infrared applications, utilizing appropriate dichroic polarisers, can also be manufactured.

Retarder Material

Nematic liquid crystal with Birefringent polymer

Polarizer Material

Dichroic polymer

Substrate Material

Optical quality synthetic fused silica

Contrast Ratio

500:1 at single wavelength

Transmitted Wavefront

Distortion (at 632.8 nm) ≤ λ/4 (each component)

Surface Quality

40 – 20 scratch‐dig

Beam Deviation

≤ 2 arc min

Reflectance (per surface)

≤ 0.5% at normal incidence

Diameter Tolerance

±0.005 in.

Temperature Range

0˚C to + 50˚C

spectral regions

We offer standard liquid crystal variable attenuators to cover four spectral regions:
VIS: 450 – 700 nm
IR 1: 650 – 950 nm
IR 2: 900 – 1250 nm
IR 3: 1200 – 1700 nm

LC-Variable Attenuator
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LVA Series

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If you’re interested in the products shown here, or have questions about something you can’t find on our website, please get in touch through the form below.

Our knowledgeable sales team will be happy to help. We can normally source exactly what you need, or work with you to come up with custom solutions.

Alternatively, just call +44 (0) 1933 461 666 and ask to speak to the Photonics team.

Ask the Expert

If you’re interested in the products shown here, or can’t find exactly what you need, please get in touch with our specialist through the form below.

Alternatively, just call +44 (0) 1933 461 666 and ask to speak to Toby.

Toby Scrivener

MPhys (Hons)

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If you’re interested in the products shown here, or can’t find exactly what you need, please get in touch with our specialist through the form below.

Alternatively, just call +44 (0) 1933 461 666 and ask to speak to Karen.

Karen McGeachy West

MPhys (Hons)

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If you’re interested in the products shown here, or can’t find exactly what you need, please get in touch with our specialist through the form below.

Alternatively, just call +44 (0) 1933 461 666 and ask to speak to Peter.

Peter Collins

Peter Collins

BEng (Hons), MSc (Eng)

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Alternatively, just call +44 (0) 1933 461 666 and ask to speak to Sian.

Siân Brooks

BSc (Hons)

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Dan Young

BSc (Hons)

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Paul Williams

PhD

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Lisa Thomson

MPhys

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Alternatively, just call +44 (0) 1933 461 666 and ask to speak to Shannon.

Shannon O’Connor

BSc (Hons)