What is M2 - Lee Laser, Inc.

More documents

Recommendations

Info

2It should be remembered that the M 2 value of 1.0 for a laser is the ideal, theoretical limit. Noactual laser meets this theoretical limit. Only the most sophisticated scientific lasers evenapproach the theoretical limit of 1.0 for M 2 .Why does Lee Laser not use M 2 ?Lee Laser prefers not to use the value of M 2 to indicate the beam quality of our laser products.M 2 cannot be measured; it is a value that is calculated from other parameters that aremeasured. As a practical matter, it is much more difficult to use the value of M 2 to determinethe focus potential of a laser, or the focus spot diameter when a laser is used with a particularset of beam delivery optics:wheres = 4(M 2 ) f/ Ds = diameter of the beam focus spot, in mf = focal length of the focusing lens, in mmRather, Lee Laser prefers simply to use the values of beam diameter, D, and beamdivergence, , that we publish in our specifications data sheets. With these values, thediameter of a beam focus spot may be calculated simply by the expressions:1. Focus Spot Potential of a Laserwhereors = FDF = the F# of the focus lens (in this case, a beam expander must be adjusted to sothat the beam completely fills the input clear aperture of the focus lens)2. Focus Spot Diameter (when a laser is used with a particular set of beam delivery optics)wheres = f 11 = full-angle divergence of the beam as it enters the focus lens (will be different fromif a beam expander is used), in mr
M 2 and Lee Laser Specifications Data Sheets3Specifications data sheets for Lee Laser products do not state the M 2 values of the lasers.Rather, we state the beam diameter and full-angle beam divergence values that a lasertypically exhibits. This information is much more useful to our customers that must calculatethe beam focus capability of a laser. This calculation from the M 2 value is much more difficult.Furthermore, the value of beam waist diameter of a laser that is needed to calculate M 2 is notthe same as the value of beam diameter that Lee Laser states in our data sheet:1. Beam Diameter for Data Sheet: Actual measured value about 10 inches (25 mm) fromthe output end of the laser.2. Beam Diameter for M 2 Calculation: This is the beam waist diameter which is located atthe reflective surface of the laser output coupler. Because access is not possible tomeasure this dimension, it must be calculated from beam diameter measurements thatare taken at different distances from the output end of the laser.Clearly, Lee Laser s published value for laser beam diameter cannot be used as the beamwaist value to calculate M 2 .The Benefit of Using M 2What is the benefit of using the M 2 value of a laser ? Within the laser industry, there existssome disagreement about the meaning of beam divergence and beam size. Somecompanies list in their data sheets only the half angle for beam divergence, and list only thebeam radius for beam size. Therefore, the mm-mr product that is used by many lasermanufacturers does not clearly define the performance of a laser, and for two identical lasersit can differ by as much as a factor of 4.However, the expression of M 2 as defined above is universally recognized within the laserindustry. Therefore, M 2 can be a valuable tool when comparing the performance of two lasersthat are manufactured by different companies, or even of two lasers by the same company.
Page 1: What is M 2 ?Recently, there has be

What is M2 - Lee Laser, Inc.

Create successful ePaper yourself

Delete template?

Save as template?