Thin Substrate, Dichroic and Polychroic Thin Film Filters Featuring Flatness
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Thin Substrate, Dichroic and Polychroic Thin Film Filters Featuring Flatness < 0.1 Waves RMS Alluxa Engineering Staff December 2012

Alluxa Introduces a New Line of Ultra-Flat Dichroic and Polychroic High Performance Thin Film Filters that Feature a Flatness of <0.1wave RMS Without the Need for Backside Compensation. Alluxa is introducing a new line of thin substrate ultra-flat dichroics and polychroic filters for use in imaging applications that require flatness levels exceeding 0.1 waves RMS per inch. These filters are unique because they achieve flatness by eliminating the high stresses of asdeposited traditional ion-based coating process such as Ion Beam Sputtering (IBS) and Ion Assisted Deposition (IAD). Alluxa’s...

using a technique known as “backside compensation.” In simplistic terms, this compensation technique involves coating both sides of the substrate with a coating that will balance out the stress of the filter and, therefore, flatten the surfaces. The downside of this technique is also straightforward: it can nearly double the amount of coating required and significantly increase the manufacturing cost of the filters. Following the widespread use of dichroic filters, the need for more complex filters has emerged over the past two decades. Now, applications such as Pinkel and Sedat style...

Figure 3. Triple bandpass polychroic on a 1.0 mm thick fused silica substrate with measured flatness of< 0.25 Waves/inch RMS @ 632.8 nm. Figure 4. Dual notch polychroic on a 0.5 mm thick fused silica substrate with measured

Specifying Dichroic and Polychroic Filters Specifying dichroics and polychroics filters primarily involves selecting the desired pass bands, blocking bands, substrate type, and thickness. The spectral gaps between the bands is the primary driver of coating complexity and cost. 45 degrees is a standard angle, but the lower the angle the easier it is to achieve performance of slope, blocking and transmission. Similarly, the lower the angular range of the beam, and more collimated, the better the performance in general. Table 1 shows a summary of recommended specifications for polychroic and...

Summary The filters used by fluorescence detection systems are arguably the most important element defining the system performance. Alluxa’s new line of thin substrate ultra-flat dichroics and polychroic filters provide improved optical performance, achieve near zero net stress on the primary coated side, and require only a simple AR coating on the back. Eliminating backside compensation lowers costs, improves transmission levels, reduces scatter and improves transmitted wave-front. Flatness levels of < 0.1 waves RMS at 632 for a one inch part are achievable at thicknesses ranging from...