Optical fused silica · Material selection
JGS1 vs JGS2 vs JGS3 quartz glass grades
A technical comparison and selection guide for optical fused silica. JGS1, JGS2 and JGS3 are different spectral classes — not a low / medium / high quality ranking.
Direct answer
JGS1 is synthetic fused silica for deep-UV work (typically ~185–2500 nm, high OH). JGS2 is natural fused quartz for UV–visible optics (typically ~220–2500 nm). JGS3 is low-OH fused quartz for infrared paths that must clear the 2.73 μm water band (typically ~260–3500 nm). They differ by raw material, melting method, OH content, impurity level and transmission — not by which number is “best”.
JGS1
Deep UV · synthetic
~185–2500 nm
High OH is a UV-grade trait, not a quality defect.
JGS2
UV–visible · natural
~220–2500 nm
The economical optical grade when deep UV is not required.
JGS3
IR · low OH
~260–3500 nm
Selected to clear the 2.73 μm water band.
Core comparison
JGS1 vs JGS2 vs JGS3: property comparison
This is a material-selection table, not a quality ranking. Numbers are typical industry values. Thermal expansion is a fused-silica property and is essentially the same across grades.
| Property | JGS1 | JGS2 | JGS3 |
|---|---|---|---|
| Material type | Synthetic fused silica | Natural fused quartz | Low-OH fused quartz |
| Raw material | SiCl₄ (silicon tetrachloride) or equivalent synthetic precursor | High-purity natural quartz crystal | Natural quartz crystal, electrically fused |
| Manufacturing method | Flame hydrolysis / CVD in an oxyhydrogen flame | Oxyhydrogen flame fusion of natural crystal | Vacuum / electric fusion (low-OH route) |
| SiO₂ purity Typical | Highest of the three; metallic impurities typically lowest | High; more metallic impurities than JGS1 | High SiO₂; metallic impurities typically highest of the three |
| OH content Typical | ~1,000–2,000 ppm | ~100–200 ppm | <5–20 ppm |
| Metallic impurities Typical | Typically ~5 ppm | Typically 20–40 ppm | Typically 40–50 ppm |
| Bubble / inclusion level Typical | Typically bubble-free; highest optical cleanliness | May contain striae or particle structure | May contain bubbles; can limit precision optics |
| Homogeneity Typical | Highest of the three JGS grades | Good; confirm quality class for wavefront-critical work | Lower; bubbles and birefringence can be limiting |
| UV transmission Typical | Deep UV; typical useful window from ~185 nm | UV from ~220 nm; not the deep-UV grade | Limited UV; typical useful start ~260 nm |
| Visible transmission Typical | Excellent | Excellent — usual workhorse for visible windows | Good; bubbles may affect scatter-sensitive paths |
| Near-IR transmission Typical | Good except OH combination bands | Good except OH combination bands | Excellent — OH bands largely removed |
| IR transmission Typical | Limited by OH absorption near 2.73 μm; practical to ~2.5 μm | Same OH limitation near 2.73 μm; practical to ~2.5 μm | Clean through the 2.73 μm water band; useful to ~3.5 μm |
| Thermal expansion Same | ~5.5 × 10⁻⁷ /°C (20–320°C) | ~5.5 × 10⁻⁷ /°C (20–320°C) | ~5.5 × 10⁻⁷ /°C (20–320°C) |
| Typical applications | Deep-UV optics, 193/248 nm paths, UV spectroscopy windows | General optical windows, UV–Vis lab optics, sight glasses, UV sleeves | IR windows, thermal imaging, IR spectroscopy, 2.7 μm paths |
| Relative cost Typical | Highest | Lowest of the three optical grades | Typically mid |
Metallic-impurity and birefringence figures in vendor catalogues are not FGQuartz certificates of analysis. Transmission cut-ons shift with thickness, surface finish and lot.
Optical transmission by wavelength band
Which band you need decides the grade — not which grade “sounds” more advanced. This maps common working bands to the typical grade.
| Band | Examples | Typical grade | Reason |
|---|---|---|---|
| Deep UV (< ~220 nm) | 185 nm, 193 nm ArF, 200 nm | JGS1 | Synthetic fused silica is the grade with usable deep-UV transmission. |
| UV (≈220–400 nm) | 248 nm KrF, 254 nm, 365 nm | JGS1 or JGS2 | Below ~220 nm, JGS1. Near 248–254 nm, JGS1 is conservative; JGS2 may suffice depending on thickness and required transmission. |
| Visible | 400–700 nm | JGS2 (typical) | All three transmit visible light; JGS2 is usually the economical optical grade. |
| Near IR | 800–2500 nm, 1064 nm | JGS2 or JGS3 | JGS2 is often enough until the path approaches the 2.73 μm OH band. |
| Mid IR / 2.7 μm region | 2.5–3.5 μm, 2.73 μm | JGS3 | Low OH is what clears the water-absorption band that limits JGS1 and JGS2. |
Widely published spectral-class reference values for a 10 mm unpolished blank. These are industry reference tables, not FGQuartz measured lot data.
JGS1
| 185 nm | > 85% |
| 200 nm | > 85% |
| 220 nm | > 85% |
| 240 nm | > 87% |
| 300 nm | > 90% |
| 185–1200 nm | No absorption peak |
JGS2
| 220 nm | > 80% |
| 240 nm | > 75% |
| 300 nm | > 80% |
JGS3
| 2.0 μm | > 90% |
| 2.5 μm | > 90% |
| 2.7 μm | > 90% |
| 2.8 μm | > 85% |
| 0.2–2.8 μm | No absorption peak |
JGS1
What is JGS1 quartz glass?
JGS1 is synthetic fused silica in the Chinese optical-grade system — far-ultraviolet optical quartz glass. It is made from a high-purity silicon precursor, typically silicon tetrachloride (SiCl₄), by flame hydrolysis in an oxyhydrogen flame (Type III fused silica analogue). The result is a very clean, highly homogeneous glass with low metallic impurities and high hydroxyl (OH) content.
High OH is not a defect in JGS1. The same synthesis route that introduces OH also produces the lowest metallic-impurity, bubble-free network that remains transmitting in the deep UV. Typical published windows are about 185–2500 nm. Industry class-1 tables for a 10 mm blank call for >85% at 185 nm — not a guaranteed 90% at every thickness.
Why is JGS1 used for deep UV?
JGS1 is typically selected when transmission in the deep-UV range is required, subject to the exact wavelength, thickness and optical specification. Metallic impurities and structural defects in natural fused quartz absorb below ~220 nm. Synthetic flame-hydrolysed silica avoids that UV edge.
- 193 nm (ArF) and 248 nm (KrF) — JGS1 is the matching spectral class for excimer paths. Lithography-grade homogeneity, induced absorption and laser-damage threshold are extra specifications; they are not automatic with the name “JGS1”.
- UV lithography, inspection and spectroscopy — deep-UV windows, cuvettes and beam paths where the short-wavelength edge matters.
- Trade-off — the OH stretching band near 2.73 μm makes JGS1 a poor infrared window despite excellent UV performance.
JGS2
What is JGS2 quartz glass?
JGS2 is optical fused quartz melted from high-purity natural quartz crystal in an oxyhydrogen flame (Type II analogue). It is not “lower-quality JGS1”. It is a different optical-performance profile: moderate OH (typically ~100–200 ppm), usable UV from about 220 nm, strong visible transmission, and a lower cost than synthetic deep-UV material.
Typical published window: about 220–2500 nm. Large pieces may show striae; confirm optical quality class when transmitted wavefront matters. JGS2 still carries an OH absorption band near 2.73 μm, so it is not an IR-grade substitute for JGS3.
When is JGS2 enough?
JGS2 is typically enough when the application is a general UV–visible optical window, sight glass, laboratory optic, UV-sterilisation sleeve or viewport that does not require transmission below ~220 nm and does not need a clear 2.7 μm path. Over-specifying JGS1 for those jobs is a common way to overpay.
JGS3
What is JGS3 quartz glass?
JGS3 is infrared optical fused quartz made by a low-OH route, typically vacuum / electric fusion of natural quartz (Type I analogue). Hydroxyl is driven down to typically <5–20 ppm so the 2.73 μm water band is largely removed. Typical published window: about 260–3500 nm.
Electrically fused natural quartz usually carries more metallic impurities than synthetic JGS1, so the UV edge is worse — often around 260 nm, not 185 nm. Some catalogues list 185–3500 nm; that description usually belongs to dry synthetic (Type IV) silica, not to standard electrically fused JGS3. Do not treat JGS3 as a 1:1 equivalent of Heraeus Suprasil 300.
Why is low OH important for infrared applications?
Hydroxyl in the silica network absorbs strongly near 2.73 μm (and more weakly at related combination bands). If the instrument, sensor or thermal-imaging path must transmit there, high-OH JGS1 is the wrong material even though it is the “premium” UV grade. Low OH is an infrared transmission requirement, not a purity trophy.
Why does OH content matter?
OH (hydroxyl) is water-related Si–OH in the glass network. In fused silica it is both a process fingerprint and an optical absorber.
- Infrared: the fundamental OH stretch sits near 2.73 μm. High-OH JGS1 and moderate-OH JGS2 show a deep transmission dip there. Low-OH JGS3 is made to clear that dip.
- UV: JGS1’s high OH does not make it a worse UV material. The flame-hydrolysis route that leaves high OH also produces the cleanest deep-UV silica in this family.
- Selection rule: high OH is a UV-grade characteristic; low OH is an IR-grade characteristic. Neither is “better” in the abstract.
JGS1 vs JGS2
Direct answer: JGS1 is synthetic fused silica for deep UV; JGS2 is natural fused quartz for general UV–visible work. Choose JGS1 when the path is below ~220 nm, or when the drawing requires synthetic / highest homogeneity. Choose JGS2 when UV–visible transmission is enough and cost matters.
| Question | JGS1 | JGS2 |
|---|---|---|
| Feedstock | Synthetic (SiCl₄) | Natural quartz crystal |
| OH | High (~1000–2000 ppm typical) | Moderate (~100–200 ppm typical) |
| UV | Deep UV from ~185 nm | From ~220 nm |
| Homogeneity | Highest / typically bubble-free | May contain striae |
| Cost | Highest | Lowest optical grade |
| When necessary | Deep UV, 193/248 nm, critical UV optics | General UV–Vis windows and sight glasses |
JGS2 vs JGS3
Direct answer: JGS2 is the UV–visible workhorse with residual OH; JGS3 is the low-OH infrared grade. The 2.73 μm absorption band is the practical dividing line. Cost usually places JGS2 below JGS3, but the decision is spectral, not price-first.
- JGS2: moderate OH, better UV than typical JGS3, limited by the water band in the IR.
- JGS3: very low OH, cleaner 2.5–3.5 μm path, typically weaker deep UV, possible bubbles.
JGS1 vs JGS3
Direct answer: JGS1 and JGS3 are not high and low versions of the same glass. JGS1 is a deep-UV, high-OH synthetic. JGS3 is a low-OH infrared fused quartz. The grade number does not mean quality. Working wavelength does.
A 193 nm window that is “upgraded” to JGS3 will usually fail the UV requirement. An IR window that is “upgraded” to JGS1 will usually fail at 2.73 μm. Specify the spectrum, then the grade.
Can JGS1, JGS2 and JGS3 be used interchangeably?
No. They are not interchangeable by default. A drawing that says “Material: JGS1” is a specification, not a suggestion. Do not ship JGS2 or JGS3 in its place without written customer confirmation — and the reverse is equally true.
Substitution can be discussed only after wavelength, required transmission at thickness, OH absorption, optical quality, homogeneity, application and the customer specification are on the table. Visible-only windows sometimes allow more than one grade optically, but bubbles, fluorescence, scatter and cost still differ.
Are JGS grades necessary for every quartz glass product?
No. Optical-grade fused silica and process-grade fused quartz are different buying decisions. Furnace tubes, quartz boats, crucibles and most structural components are specified for temperature resistance, chemical resistance, purity and dimensional stability — not for a JGS transmission band.
Do not write JGS1/JGS2/JGS3 onto every quartz glass RFQ. Use a JGS grade when the part is an optical path (window, viewport, UV envelope, IR window, polished optic). Use process-grade fused quartz when it is not. See What is quartz glass? and quartz glass tubes.
How to choose between JGS1, JGS2 and JGS3
Step 1. What wavelength does the application use?
The shortest and longest wavelengths in the optical path decide the grade more than any other question.
Step 2. Does it require deep-UV transmission?
If the path is below ~220 nm, JGS1 is the typical spectral class.
Step 3. Does it require low OH for IR?
If the path includes ~2.73 μm or must stay open toward ~3.5 μm, JGS3 is the typical class.
Step 4. What optical quality is required?
Homogeneity, bubbles, striae, scratch-dig and flatness are specified in addition to grade.
Step 5. What thickness is required?
Cut-on wavelength and OH-band depth both move with thickness.
Step 6. Does the drawing already name a grade?
If it does, that grade is the requirement until the customer changes it in writing.
Step 7. Is an optical grade actually necessary?
If the part is not an optical path, process-grade fused quartz is usually correct.
Decision table
“Likely grade” is not “guaranteed grade”. Edge-of-band work needs a transmission requirement at thickness.
| Requirement | Likely grade | Reason |
|---|---|---|
| Deep UV transmission | JGS1 | Synthetic fused silica is specified when the path is below ~220 nm. |
| 193 nm (ArF) path | JGS1 | JGS1 is the matching spectral class. Lithography-grade homogeneity and laser-damage specs are additional and must be stated separately. |
| 248 nm (KrF) path | JGS1 (typical) | JGS1 is the conservative choice. Do not assume JGS2 without a transmission requirement at thickness. |
| General UV / visible window | JGS2 (typical) | Most UV–Vis windows do not need deep-UV synthetic material. |
| IR transmission past ~2.5 μm | JGS3 | Low OH removes the 2.73 μm absorption that cuts JGS1 / JGS2. |
| Specified low-OH material | JGS3 | Low OH is the defining IR-grade requirement, not a quality ranking. |
| General optical window (no deep UV, no 2.7 μm) | JGS2 (typical) | Best cost-to-performance among the optical grades for this band. |
| IR window / thermal imaging | JGS3 | Selected for the infrared window, not because it is “higher grade.” |
| Furnace tube, boat, crucible, structural part | Process-grade fused quartz (not a JGS blank) | Thermal, chemical and dimensional requirements dominate; optical JGS is usually unnecessary. |
Selection flowchart
- Working wavelength known?
- Deep UV (below ~220 nm, including 193 nm) → JGS1
- IR / 2.73 μm / low OH required → JGS3
- UV–visible / general optical window → JGS2 (typical)
- Not an optical path → process-grade fused quartz, not a JGS blank
Applications
Where each grade is actually used
Applications below match the spectral class. If the part is not an optical path, see process-grade fused quartz instead.
JGS1 applications
- Deep-UV optics and windows
- Excimer laser paths (193 nm ArF, 248 nm KrF) when the spectral class is JGS1
- UV lithography / inspection optics (grade plus wavefront/damage specs as required)
- UV spectroscopy windows and sample cells
- UV optical windows where the short-wavelength edge is specified
Only list JGS1 when the UV edge actually requires synthetic fused silica.
JGS2 applications
- General optical windows and plates
- UV–visible laboratory optics
- Sight glasses and viewports in the UV–Vis
- UV sterilisation sleeves where deep UV below ~220 nm is not required
- Cost-sensitive polished windows that still need optical-grade material
JGS2 is the default optical grade for many UV–Vis jobs — not a compromise JGS1.
JGS3 applications
- Infrared windows
- Thermal imaging viewports
- IR spectroscopy paths that include the 2.7 μm region
- Broadband systems that must remain open past the water band
Do not assign JGS3 to deep-UV work because the number is higher.
FGQuartz components in these grades
Once the grade is chosen, the usual next step is a plate, window or custom optic — not a catalogue SKU named after the grade. If you already know you need JGS2, start with JGS2 windows. If you do not, send wavelength and application.
Engineering inquiry
What to provide when requesting JGS quartz glass
A complete RFQ avoids a second round of questions. FGQuartz reviews drawings and typically replies within 24 business hours. No minimum order quantity for prototypes.
- JGS grade (or “advise grade”)
- Working wavelength(s)
- Component type (window, plate, tube, lens blank, custom)
- Dimensions and tolerances
- Thickness
- Clear aperture
- Surface quality (e.g. scratch-dig)
- Flatness / transmitted wavefront
- Parallelism
- Coating requirement (if any)
- Quantity
- Drawing (DXF, STEP, IGES or PDF)
FAQ
Short answers for search and AI overviews. Details live in the sections above.