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Computer Controlled Variable Attenuator for Tunable Lasers

Computer Controlled Variable Attenuator for Tunable Lasers
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A p p l i c a t i o n K i t s 277 Email: sales@spectra-physics.com • Web: spectra-physics.com Application Kits Educational Kits Computer Controlled Variable Attenuator for Tunable Lasers • Automatic control and adjustment of output power of fixed power lasers • Designed to work with Spectra-Physics Ti:Sapphire ultrafast lasers • All parts selected and tested to work together • Produces either horizontal or vertical output polarization Applications • Multiphoton Microscopy • Supercontinuum Generation • Terahertz Generation • Ultrafast Spectroscopy • Optical Coherence Tomography The Newport Computer Controlled Variable Attenuator Kit (CCVA) is an easy to use kit for the continuous, automatic attenuation of the laser output power. The CCVA application note describes a closed loop computer controlled variable attenuator for the control of output power from a tunable laser. It is based on the combination of a 1/2 wave-plate and polarizer. The algorithm used to control power operates in a closed loop with PID (proportional, integral, derivative) feedback, compensating for slow changes in output power. For the manual variable attenuator, the power is measured directly at the output of the attenuator for each wavelength and set accordingly by rotating the 12 wave-plate. In contrast, the computer controlled closed loop attenuator sets and maintains the power by positioning the 12 wave-plate based on a feedback signal from a photo detector which can exhibit a strong dependence on wavelength. This chromaticity becomes significant when the tuning range is large. Consequently, a spectrometer is incorporated into the setup which provides real-time information about the wavelength of the laser, thus taking advantage of the precise wavelength calibration of the photo-detector. This is especially important when the laser power needs to be held constant while scanning wavelength. Depending on the choice of components the attenuator is suitable for laser wavelengths ranging from 400 nm to 1100 nm, and average powers from 1nW up to 20 Watts (500 Watts/cm2 damage threshold). This device is capable of attenuating light by a factor of 1000 while still maintaining an error of less than 10%. The algorithm used to control power operates in a closed loop with PID (proportional, integral, derivative) feedback, compensating for slow changes in output power within the bandwidth of the device greater than 500 ms. Ordering Information Model Description CCVA-TL-KT Computer controlled variable attenuator M-CCVA-TL-KT Computer controlled variable attenuator, metric

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