{"id":3638,"date":"2026-10-23T09:37:37","date_gmt":"2026-10-23T01:37:37","guid":{"rendered":"http:\/\/www.corrchess-by.com\/blog\/?p=3638"},"modified":"2026-10-23T09:37:37","modified_gmt":"2026-10-23T01:37:37","slug":"what-is-the-dispersion-uniformity-of-seya-namioka-flat-field-concave-holographic-grating-49fa-18ef96","status":"publish","type":"post","link":"http:\/\/www.corrchess-by.com\/blog\/2026\/10\/23\/what-is-the-dispersion-uniformity-of-seya-namioka-flat-field-concave-holographic-grating-49fa-18ef96\/","title":{"rendered":"What is the dispersion uniformity of Seya – Namioka Flat – Field Concave Holographic Grating?"},"content":{"rendered":"

Hey everyone, if you\u2019ve ever worked with spectrometers, monochromators, or any optical analytical gear, you\u2019ve probably run into Seya-Namioka flat-field concave holographic gratings. But let\u2019s cut to the chase\u2014today we\u2019re talking about one of their most critical performance metrics that makes or breaks your measurements: dispersion uniformity. As a supplier of these gratings, I can\u2019t tell you how many times customers hit me up saying, \u201cMy readings are off, why?\u201d Half the time, it comes down to not understanding what dispersion uniformity actually is, and why it matters more than just raw dispersion numbers. Seya-Namioka Flat-Field Concave Holographic Grating<\/a><\/p>\n

<\/p>\n

First, let\u2019s get the basics straight: a concave holographic grating isn\u2019t just a plain diffraction grating. It\u2019s etched (holographically, so we use laser interference, not traditional ruling) onto a concave surface, which means it does two jobs at once: disperses light like a regular grating and<\/em> focuses it, so you don\u2019t need extra mirrors. The Seya-Namioka configuration specifically is a classic off-axis design used in many compact spectrometers\u2014great for labs, field tools, even portable device stuff. Now, dispersion itself is how much the grating spreads out different wavelengths of light; if you have high dispersion, a tiny change in wavelength gives a big shift in position, so you get sharp, separated peaks.<\/p>\n

But dispersion uniformity? That\u2019s the consistency of that spread across the entire wavelength range you\u2019re working with. Let\u2019s say your monochromator covers 200 nm to 800 nm (UV to visible). If your dispersion is 1.2 nm\/mm at 200 nm, and 2.8 nm\/mm at 800 nm, that\u2019s a huge jump\u2014that\u2019s<\/em> bad uniformity. Why? Because your calibration (the numbers you set to convert position to wavelength) only works for one spot; across the range, your readings will drift, peaks won\u2019t line up right, and if you\u2019re doing quantitative work (like measuring protein absorption or heavy metal traces), your data will be unreliable.<\/p>\n

Wait, let\u2019s make that concrete. I had a customer last year who runs a portable spectrometer for water testing. They were testing for lead, and their results kept coming back inconsistent\u2014one sample would show 5 ppb, the next 8 ppb, same water. Turned out their old grating had terrible dispersion uniformity: at the lead test wavelength (283 nm), dispersion was 1.1 nm\/mm, but at the next calibration point (400 nm), it was 2.5 nm\/mm. They were setting the same position offset for both, so their wavelength calibration was way off. Swapped to our Seya-Namioka flat-field grating, which has a uniformity error under 3%, and their results stabilized within 24 hours. That\u2019s the kind of real, daily problem this metric solves.<\/p>\n

Now, how do we measure it? When we make a holographic concave grating, we don\u2019t just etch lines randomly\u2014we use two interfering laser beams to create the groove pattern, and we can tweak those beams to adjust the curvature of the grooves, which directly impacts dispersion uniformity. We test it by illuminating the grating with a calibrated light source (like a tunable laser) across the full wavelength range, mapping where each wavelength diffracts, then calculate how much the dispersion changes from end to end. For our gratings, we target uniformity of less than 3% across the operating range\u2014industry standard is usually under 5%, so that\u2019s a point we stand on.<\/p>\n

Wait, why flat-field? Oh right, Seya-Namioka gratings are flat-field, meaning the focused spectrum lands on a flat plane instead of a curved one. That\u2019s a big deal for camera sensors or linear arrays, because you don\u2019t have to adjust the sensor\u2019s shape\u2014you just mount it straight, which cuts down on assembly time and cost. But flat-field and dispersion uniformity are linked: if the groove pattern is off, both the focus and the dispersion will be uneven. For example, if you overcorrect the grooves for focus, you might get a perfect flat field, but the dispersion will warp across the wavelength range. We spend a lot of time tuning the holographic exposure to balance both.<\/p>\n

Common mistakes I see customers make: 1) Buying a grating just based on \u201cgroove density\u201d (like 1200 l\/mm or 2400 l\/mm) without checking dispersion uniformity. A 1200 l\/mm grating with 2% uniformity is way better than a 1800 l\/mm one with 7% uniformity, even if it\u2019s less \u201cdense.\u201d Density only tells you how much light it disperses, not how evenly. 2) Assuming all Seya-Namioka gratings are the same. No\u2014someone else might cut corners on holographic alignment, so their uniformity is garbage. We test every single grating we ship with a metrology system, so you don\u2019t get a dud.<\/p>\n

Another use case: UV spectroscopy, which is super common in pharma for drug testing. If a pharma lab uses a grating with bad dispersion uniformity, their absorbance readings for a drug\u2019s active ingredient will be off by enough to fail regulatory checks. We\u2019ve got a few pharma clients who\u2019ve been with us for years because we deliver gratings that pass their FDA calibration requirements\u2014another area where uniformity isn\u2019t just a nice-to-have, it\u2019s a requirement.<\/p>\n

What affects dispersion uniformity? Let\u2019s break it down a bit, in plain terms. The main thing is the holographic interference pattern. If the two laser beams we use to create the grooves aren\u2019t perfectly aligned, the groove spacing changes across the grating surface, which makes dispersion uneven. Also, the concave substrate\u2019s curvature\u2014if the substrate isn\u2019t polished perfectly flat before coating, that adds distortion. We use fused silica substrates because they\u2019re super stable, so thermal changes don\u2019t warp the grating and mess with uniformity. Ruled gratings (not holographic) are worse here, by the way\u2014their grooves are machine-cut, so there\u2019s always slight irregularities in spacing, which kills uniformity. That\u2019s why holographic is the way to go for flat-field Seya-Namioka designs.<\/p>\n

Wait, let\u2019s clarify a common mix-up: dispersion uniformity vs. resolution. Resolution is how sharp your peaks are\u2014can you tell apart two wavelengths that are really close? Dispersion uniformity is about consistency across the range. A grating can have great resolution but terrible uniformity, or vice versa. You need both, but uniformity is the backbone because if your dispersion changes, your resolution measurements will be uneven too.<\/p>\n

I get it, if you\u2019re not an optics person, this stuff can sound jargon-heavy. So let\u2019s sum it up in plain English: when you pick a Seya-Namioka flat-field concave holographic grating, dispersion uniformity is how evenly it spreads light across all the wavelengths you care about. Bad uniformity = your measurements will be inconsistent, your calibration will be wrong, and you\u2019ll end up redoing tests. Good uniformity = reliable data, less calibration hassle, and better performance from your spectrometer.<\/p>\n

<\/p>\n

Now, if you\u2019re out there shopping for these gratings\u2014whether you\u2019re building a lab spectrometer, a field water tester, or a pharma quality control tool\u2014don\u2019t sleep on dispersion uniformity. A lot of suppliers will lead with groove density or price, but those don\u2019t tell you the full story. We\u2019ve built our business on making sure every grating we ship has that uniformity under 3%, and we stand behind every one.<\/p>\n

Broadband Infrared Grating<\/a> If you\u2019re troubleshooting a current issue with your optical setup, or you\u2019re sourcing for a new project, hit us up to chat through what you need. We can walk you through the specs, explain how our gratings fit your wavelength range, and even share test data if you want to check uniformity for yourself. No sales pitch, just straight talk about what works for your application.<\/p>\n

References<\/h3>\n
    \n
  1. Palmer, C. H. (2005). Diffraction Grating Handbook<\/em>. Newport Corporation.<\/li>\n
  2. Yoshikawa, H., & Ohta, K. (1980). Flat-field concave holographic gratings for Seya-Namioka monochromators. Applied Optics<\/em>, 19(15), 2567-2572.<\/li>\n
  3. Kuroda, N., et al. (2012). Performance evaluation of holographic concave gratings for UV-Vis spectroscopy. Journal of Optical Technology<\/em>, 79(10), 652-656.<\/li>\n
  4. Bennett, J. M. (1995). Principles of holographic grating fabrication. Optical Engineering<\/em>, 34(3), 821-830.<\/li>\n<\/ol>\n
    \n

    Jilin Juyao Technology Co., Ltd.<\/a>
    As one of the leading seya-namioka flat-field concave holographic grating manufacturers and suppliers in China, we offer a wide range of products with superior quality. Please feel free to wholesale customized seya-namioka flat-field concave holographic grating from our factory. Welcome to view our website for more information.
    Address: Room 101, No. 2 Huiwen Road, Nanguan District, Changchun City, Jilin Province, China
    E-mail: jyoptix@outlook.com
    WebSite:     https:\/\/www.jyoptix.com\/<\/a><\/p>\n","protected":false},"excerpt":{"rendered":"

    Hey everyone, if you\u2019ve ever worked with spectrometers, monochromators, or any optical analytical gear, you\u2019ve probably … What is the dispersion uniformity of Seya – Namioka Flat – Field Concave Holographic Grating?<\/span>Read more<\/a><\/p>\n","protected":false},"author":207,"featured_media":3638,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3601],"class_list":["post-3638","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-seya-namioka-flat-field-concave-holographic-grating-46eb-191f54"],"_links":{"self":[{"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/posts\/3638","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/users\/207"}],"replies":[{"embeddable":true,"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/comments?post=3638"}],"version-history":[{"count":0,"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/posts\/3638\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/posts\/3638"}],"wp:attachment":[{"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/media?parent=3638"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/categories?post=3638"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.corrchess-by.com\/blog\/wp-json\/wp\/v2\/tags?post=3638"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}