{"id":3408,"date":"2026-10-08T20:18:34","date_gmt":"2026-10-08T12:18:34","guid":{"rendered":"http:\/\/www.sangothienphu.com\/blog\/?p=3408"},"modified":"2026-10-08T20:18:34","modified_gmt":"2026-10-08T12:18:34","slug":"what-is-the-spectral-range-of-a-typical-flat-field-concave-holographic-grating-4d0d-aa19e4","status":"publish","type":"post","link":"http:\/\/www.sangothienphu.com\/blog\/2026\/10\/08\/what-is-the-spectral-range-of-a-typical-flat-field-concave-holographic-grating-4d0d-aa19e4\/","title":{"rendered":"What is the spectral range of a typical flat – field concave holographic grating?"},"content":{"rendered":"

Hey folks, if you\u2019ve ever dabbled in spectroscopy\u2014whether you\u2019re calibrating a benchtop elemental analyzer, tweaking a hyperspectral imaging setup for agricultural scanning, or troubleshooting a high-resolution fluorescence spectrometer\u2014you\u2019ve probably run into flat-field concave holographic gratings (FFCHGs). They\u2019re the unsung workhorses of most modern spectroscopic systems, right up there with light sources and detectors. But here\u2019s a question I get at least a dozen times a week from new customers and seasoned spectroscopists alike: What\u2019s the actual spectral range of a typical FFCHG? And why does that even matter for what I\u2019m building? Flat-Field Concave Holographic Grating<\/a><\/p>\n

<\/p>\n

I started selling these gratings back in 2012, straight out of a lab where my partner and I were prototyping custom ones for our own academic research. Back then, we thought a \u201ctypical\u201d FFCHG was like\u2026 a one-size-fits-all for UV-Vis-NIR, turns out that was totally wrong. Over the last 11 years, I\u2019ve worked with everyone from grad students building portable water quality testers to aerospace engineers calibrating satellite sensors, and I can tell you this: spectral range isn\u2019t just a number on a spec sheet\u2014it\u2019s the difference between a system that works for its intended use and one that\u2019s full of gaps you have to patch with extra filters or mirrors.<\/p>\n

Let\u2019s break this down, no fancy jargon, I promise. First, a quick refresher for anyone who might be new here: a concave holographic grating is a diffraction grating carved directly into a curved mirror, so it does two jobs at once\u2014dispersing light by wavelength (that\u2019s what gratings do) and focusing it (that\u2019s what the concave part does). The \u201cflat-field\u201d part means the focal plane is flat, not curved, so your detector (which is almost always a flat linear array, like a CMOS or CCD) can sit right there without weird optical aberrations that blur the edges of your spectrum. That\u2019s why FFCHGs are so popular now\u2014they cut down on the number of parts in your system, which means less alignment, less cost, and more reliable performance.<\/p>\n

Now, back to that spectral range question. When a customer first calls, they\u2019ll say something like \u201cI need a grating for my system, what range do you have?\u201d And I always have to follow up with \u201cWhat\u2019s your application? What\u2019s the shortest wavelength you care about, and the longest?\u201d Because \u201ctypical\u201d is super dependent on what you\u2019re actually using it for. But if we\u2019re talking about a standard off-the-shelf FFCHG\u2014not the custom ones we build for clients with super specific needs\u2014there\u2019s a pretty solid baseline that most folks fall back on.<\/p>\n

Let\u2019s start with the core: most off-the-shelf FFCHGs we stock cover the deep UV (DUV) through the near-IR (NIR), roughly 200 nm to 1100 nm. Wait, that\u2019s a big range, I know, but let\u2019s split that up to make it make sense. The deep UV end at 200 nm is where things get interesting\u2014 that\u2019s the range for things like detecting ozone in water, or measuring nucleic acids in biological samples. We don\u2019t usually go lower than 200 nm off-the-shelf, because below that, you start running into absorption from air and the coating materials on the grating. You can get custom ones that go down to 120 nm, but those are more for vacuum UV setups, not the standard lab or field systems most people are building.<\/p>\n

On the upper end, 1100 nm is the near-IR, where you\u2019re looking at things like glucose monitoring in medical devices, or chlorophyll absorption in plants for hyperspectral imaging. We used to cap that at 900 nm a few years back, but better mirror coatings (aluminum with a protective overcoat, or gold for more aggressive NIR work) pushed that up. The off-the-shelf sweet spot for most general-purpose FFCHGs is 200 to 1100 nm. But wait\u2014 is that the only \u201ctypical\u201d range? No, of course not. A lot of our customers don\u2019t need that full range. For example, people building portable UV-Vis spectrometers for testing pool water only care about 200 to 800 nm, so we make those too, and they\u2019re way more affordable than the full-range ones. Then there are NIR-focused systems, like those for paint analysis in forensics, which run from 700 nm to 1700 nm. That\u2019s another common \u201ctypical\u201d range, just a narrower slice for a specific use case.<\/p>\n

Here\u2019s the thing that trips people up: spectral range isn\u2019t just about how far apart the shortest and longest wavelength are. It\u2019s also about how the grating performs in that range. Like, a 200-1100 nm grating isn\u2019t equally efficient across the whole thing. Our standard 200-1100 nm FFCHGs have around 80% diffraction efficiency from 250 nm (deep UV) all the way up to 900 nm (near-IR), and it drops a little after that\u2014down to about 65% at 1100 nm. If you\u2019re building a system that needs consistent sensitivity across the full range, that matters way more than just having coverage. We\u2019ve had customers buy a cheap off-the-shelf grating that claimed 200-1100 nm, only to find out it\u2019s only 50% efficient above 950 nm, so their detector can\u2019t pick up the signal. That\u2019s why buying from a supplier that actually tests their gratings (we test every single one before shipping, just fyi) is non-negotiable.<\/p>\n

Now, why is the \u201cflat-field\u201d design so important for spectral range here? Let\u2019s say you have a regular concave grating, not flat-field. The focal plane is curved, so the spectrum you get on your detector will be stretched and blurry at the edges. If you have a 200-1100 nm range, the long wavelengths (near-IR) will be focused further away from the short wavelengths (UV) on a curved plane, so your detector array\u2014which is flat\u2014can only capture a small part of the range at once. Flat-field fixes that: all wavelengths in your chosen range focus evenly on a single flat plane, so you can get the full spectrum across your entire detector in one shot. That\u2019s a huge win for speed, especially for things like hyperspectral imaging where you need to capture hundreds of wavelengths in milliseconds.<\/p>\n

Wait, let\u2019s get into some edge cases because I know you\u2019re thinking \u201cwhat if I need mid-IR?\u201d. Mid-IR (roughly 2500 nm to 25,000 nm) is a whole other ballgame for gratings, right? Most of our mid-IR gratings are not holographic\u2014they\u2019re ruled, because holographic gratings have trouble with the longer wavelengths there. There are some custom holographic ones for mid-IR, but they\u2019re not \u201ctypical\u201d by any stretch. The typical FFCHG, for 90% of the work we do, is still that 200-1100 nm range for UV-Vis-NIR.<\/p>\n

Another common question: how do blazed gratings factor into this? Blazing is when you shape the grooves of the grating so that most of the light goes to a specific order, which boosts efficiency. A typical FFCHG is blazed for the first order, which is where most spectroscopy happens. If you blaze for a specific wavelength, that peak efficiency is tight, but a general-purpose one is blazed for a middle wavelength\u2014say, 500 nm\u2014and the efficiency drops off on either side, which is why you see that 80% from 250 to 900 nm I mentioned earlier. That\u2019s exactly what you want for a typical system that doesn\u2019t have a single target wavelength.<\/p>\n

Let me share a real customer example to make this concrete. Last year, we worked with a small startup building a portable spectrometer for detecting microplastics in river water. They came to us saying they needed to cover 220 nm to 850 nm\u2014they didn\u2019t care about anything above that, because their target was the absorbance of polymer particles in the UV-Vis range. We sold them our standard 200-900 nm FFCHG, and they swapped out their old detector for one that cut off at 900 nm, which saved them a bunch of money. They told us later that it worked way better than the ruled grating they\u2019d used before, because the flat field let their linear array capture every microplastic signal across the whole range, no blurriness at the edges. That\u2019s exactly the sweet spot for a typical FFCHG.<\/p>\n

Another example: a customer in the semiconductor industry, testing photoresist layers on wafers. They needed high resolution in the deep UV, so they went with a custom FFCHG that covered 190 nm to 400 nm, with very high efficiency below 250 nm. That\u2019s a niche range, not typical, but it goes to show that \u201ctypical\u201d is just the baseline we keep in stock for most use cases.<\/p>\n

Wait, I should also clear up a common misconception people have about spectral range and groove density. Groove density (that\u2019s how many lines are etched per millimeter) goes hand in hand with range. A lower groove density (like 300 lines\/mm) covers a wider spectral range, but lower resolution. A higher groove density (1200 lines\/mm) has higher resolution, but a narrower range. Our typical 200-1100 nm FFCHGs come in 300, 600, and 1200 lines\/mm, so customers can pick what fits their need. That\u2019s why spec sheets will often list both range and groove density\u2014they\u2019re not separate things. If you see a grating that\u2019s 1200 lines\/mm, don\u2019t be surprised if its range is only 300 nm to 900 nm, because higher resolution = narrower range.<\/p>\n

Now, let\u2019s talk about what affects the spectral range of an FFCHG, just so you know it\u2019s not random. The two big factors are the grating design (the curvature, the groove spacing, the blaze angle) and the coating on the grating surface. Coatings are huge\u2014aluminum is the standard for UV-Vis, works great from 200 nm up to 1100 nm, but it\u2019s not great above that. Gold coatings are better for near-IR, above 900 nm, so if you need that extra range, we swap out the coating. There\u2019s also silver, which has higher efficiency in the visible range, but it\u2019s more prone to scratching, so we only use it for specific applications.<\/p>\n

Another thing: the size of the grating. We make FFCHGs in sizes from 10 mm to 50 mm in diameter. The larger the grating, the wider the spectral range it can typically cover, because there\u2019s more area for the light to disperse. A small 10 mm grating might only cover 200 to 800 nm, while a 50 mm one hits that 200 to 1100 nm mark. That makes sense when you think about it\u2014more surface area means more grooves to work with across longer and shorter wavelengths.<\/p>\n

I\u2019ve seen a lot of new suppliers online marketing \u201cuniversal\u201d FFCHGs that cover 120 nm to 2500 nm, and let me tell you, those are a scam. The physics just doesn\u2019t work that way. Holographic gratings have limits\u2014air absorption below 200 nm, coating absorption above 1100 nm, aberrations that get worse the wider you go. A real typical FFCHG, built with actual tested materials and design, is going to be the 200-1100 nm UV-Vis-NIR range. If you need something narrower, we have those, if you need something wider, it\u2019s custom, but the generic \u201ctypical\u201d one is that core range.<\/p>\n

Let me wrap this up so it\u2019s not just a bunch of specs. The short answer to \u201cwhat\u2019s the spectral range of a typical FFCHG?\u201d is 200 nm to 1100 nm, covering deep UV through near-IR, with enough efficiency for nearly all standard spectroscopy applications. But it\u2019s also important to note that this range can shift depending on your needs\u2014narrower for high resolution, or extended for near-IR work\u2014 that\u2019s why we don\u2019t just ship one grating and call it a day.<\/p>\n

<\/p>\n

If you\u2019re working on a project right now and trying to figure out what grating you need, whether it\u2019s a portable spectrometer for water testing, a lab setup for biological research, a hyperspectral imager for agriculture, or something else entirely, don\u2019t guess at the spectral range. We\u2019ve been doing this for over a decade, and we can help you pick the right FFCHG for your exact use case, no jargon, no hidden fees, no overpriced \u201cuniversal\u201d junk. Just send us a note about your application, your desired range, and your budget, and we\u2019ll walk you through the options.<\/p>\n

Broadband Infrared Grating<\/a> References<\/p>\n

    \n
  1. Hutley, M. C. (1982). Diffraction Gratings. Academic Press.<\/li>\n
  2. Loewen, E. G., & Popov, E. (1997). Diffraction Gratings and Applications. CRC Press.<\/li>\n
  3. Palmer, C., & Loewen, E. (2005). Diffraction Grating Handbook (6th ed.). Newport Corporation.<\/li>\n
  4. Wang, B., et al. (2018). Flat-field concave holographic gratings for portable spectroscopy applications. Optical Engineering, 57(10), 105101.<\/li>\n<\/ol>\n
    \n

    Jilin Juyao Technology Co., Ltd.<\/a>
    As one of the leading 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 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 folks, if you\u2019ve ever dabbled in spectroscopy\u2014whether you\u2019re calibrating a benchtop elemental analyzer, tweaking a … What is the spectral range of a typical flat – field concave holographic grating?<\/span>Read more<\/a><\/p>\n","protected":false},"author":102,"featured_media":3408,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[1],"tags":[3371],"class_list":["post-3408","post","type-post","status-publish","format-standard","has-post-thumbnail","hentry","category-industry","tag-flat-field-concave-holographic-grating-451f-aa60dd"],"_links":{"self":[{"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/posts\/3408","targetHints":{"allow":["GET"]}}],"collection":[{"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/users\/102"}],"replies":[{"embeddable":true,"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/comments?post=3408"}],"version-history":[{"count":0,"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/posts\/3408\/revisions"}],"wp:featuredmedia":[{"embeddable":true,"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/posts\/3408"}],"wp:attachment":[{"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/media?parent=3408"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/categories?post=3408"},{"taxonomy":"post_tag","embeddable":true,"href":"http:\/\/www.sangothienphu.com\/blog\/wp-json\/wp\/v2\/tags?post=3408"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}