This listing is for the sale of an Ideal Spectroscopy cavity ring down laser absorption spectroscopy cell with the following components (pictured left):

• One (1) 50 cm (20 in.) long, 304 stainless steel, 1.5" OD, 1.37" ID, vacuum gas cell with the following features:
  • Two (2) Conflat (CF) 2.75 fixed, thru-hole end flanges.
  • Two (2) 1/4" Swagelok® inlet and outlet ports.
  • One (1) 1/4" VCR® male gauge port.
• Two (2) Conflat (CF) 2.75 fixed, thru-hole adjustable mirror mounts for 1" OD optics with the following features:
  • Fits optics with variable thickness from 0.05 to 0.5" (1.3 to 13 mm).
  • 0.5" (1.3 mm) clear aperture.
  • 1/8" tube purge port.
• Two (2) Hinge Clamps for 1.5" OD tubes.
• Two (2) 1/2" diameter, 3" length, optical posts and post holders.
• All fasteners necessary for assembly.
• Mirrors sold separately

Cavity ring down (CRD) spectroscopy is an optical spectroscopic technique that measures the absolute extinction by absorption or scattering of samples. It uses highly reflective mirrors, often with reflectivities > 99.9%, to achieve effective optical pathlengths through the sample of tens or even hundreds of kilometers. This enabled detection of both extremely weak transitions and extremely small concentrations, down to the parts per trillion level. The measurement is made by firing a short laser pulse into the cell, or by quickly shuttering a continuous wave laser in resonance with the cavity, and then measuring the cells output laser intensity as a function of time. The resulting decay is fit to an exponential function and the decay constant, or ring down time, is compared with that of an empty cavity to determine the absorption coefficient. Because the decay constant is independant of initial laser intensity CRD spectroscopy is immune to noise from shot to shot laser intensity fluctuations.

This Ideal Vacuum CRD Spectroscopy Cell has a true pathlength of 51.7 cm (20.36 in). It has convenient ports for all of your experimental needs. Two 1/4" swagelok connections are designed for sample introduction and evacuation from the cell. A centered 1/4" VCR male connection is designed to connect directly to a pressure gauge for measuring total sample pressure. Each mirror mount is equipped with a 1/8" tube purge port to allow introduction of clean inert gas to prevent mirror contamination, prevent baseline drift, and extend mirror life. Two 1.5" hinge tube clamps and optical posts are included for immediate install onto your optical table without need for purchasing additional mounting hardware.

This Ideal Vacuum CRD Spectroscopy Cell is equipped with two adjustable mirror mounts for 80 TPI adjustment screws for easy optic alignment. The cavity length is not stabilized so this configuration is ideal for pulsed laser CRD measurements. High resolution continous wave laser sources can also be used by having a fast shuttering element, such as an electro-optic modulator or an acousto-optic modulator, that is set to trigger when the cavity output power crosses a threshold which is indicative of the cavity being on resonance with the laser. This will occur more often if there is a source of thermal of mechanical instability near the cell, such as a fan, air conditioning unit, or noisy vacuum pump. For greater control over cavity length and for cavity locking purposes, Ideal Vacuum sells replacement adjustment screws with internal piezo-electric elements capable of controlling the cavity length with sub-nanometer accuracy. Replacement of all three piezo-electric adjustment screws on only one mirror mount is necessary for this application.

Each cell is assembled and helium leak tested to ensure that it is leak tight before it is shipped. This is to ensure that atmospheric gases will not enter the cell to interfere with your measurement or react with your samples. It also ensures that your samples will not leak out of the cell and concentrations will remain constant over the duration of the experiment.

Mirror replacement to access a new wavelength region or replace fogged mirrors is quick and easy. Simply use a 9/64" Allen wrench to remove the three screws on the mirror mount and lift the blue aluminum piece away.

Swagelok, VCR-TM Swagelok Company