Ruby (chromium-doped single-crystal alumina) Cr:Al2O3
Al2O3 with a Cr3+ dopant (Cr:Al2O3) · trigonal
Ruby is alumina (Al2O3) grown as one crystal with a small amount of chromium (Cr3+) in place of aluminium.
Evidence level
2 of 5
Lab-measured
- 0Predicted only. No one has made it, or no measurement exists.
- 1Calculated. Only calculated or predicted values from sources.
- 2Lab-measured. Measured properties with their conditions stated.
- 3Space-relevant tests. Measured in conditions relevant to space, such as vacuum or atomic oxygen.
- 4Ground-qualified. Qualified for an application on the ground.
- 5Flown or field-proven. Flight or field results exist.
Hardness
Mohs 9
Heat
2040 °C
Laser band
680 to 1100 nm
Pulse energy in 1969
1.2 GW
Recipe, share of the weight
- Al2O3 not statedAluminium oxide host lattice
- Cr not statedChromium
Best for
Pulsed and tunable solid-state laser rods that need a hard, well-characterised crystal with a known pump band
Weakest at
Little space-qualification data: the sources read cover ground lasers, lunar ranging from Earth and one datasheet, with no ruby-specific radiation, outgassing or thermal-vacuum result
Risk at a glance
- People Low. No ruby-specific safety sheet was read
- If it fails Moderate. Light outside the specified pump or tuning band
- Corrosion No data. No corrosion data recorded
Quick facts: Cr:Al2O3
| Property | Value | Basis |
|---|---|---|
| Density | 3.98 g/cm³ | 1 sourced value |
| Thermal conductivity | 33 to 35 W/(m·K) | 2 sourced values across conditions |
| Thermal expansion (CTE) | 4.78 to 5.31 ppm/K | 2 sourced values across conditions |
| Melting point | 2,040 °C | 1 sourced value |
| Specific heat | 761 J/(kg·K) | 1 sourced value |
What is the density of Ruby (Cr:Al2O3)?
Ruby (Cr:Al2O3) has a density of 3.98 g/cm³. The source and test conditions are listed in the properties table on this page.
What is the thermal conductivity of Ruby (Cr:Al2O3)?
Ruby (Cr:Al2O3) has a thermal conductivity of 33 to 35 W/(m·K). The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the coefficient of thermal expansion of Ruby (Cr:Al2O3)?
Ruby (Cr:Al2O3) has a coefficient of thermal expansion of 4.78 to 5.31 ppm/K. The range covers 2 sourced values across the tempers, forms and test conditions the sources report; room-temperature values are used where a source states a temperature.
What is the melting point of Ruby (Cr:Al2O3)?
Ruby (Cr:Al2O3) has a melting point of 2,040 °C. The source and test conditions are listed in the properties table on this page.
What is Ruby (Cr:Al2O3) used for?
Uses recorded in the sources include Cr:Al2O3 laser rods for solid-state lasers; Pulsed ruby laser ranging to the Apollo 11 retroreflector (Lick Observatory, 1969); Pulsed ruby laser lunar-ranging station at McDonald Observatory (2.7 m telescope).
Why it exists
Ruby is alumina with a chromium dopant. Its datasheet gives a density of 3.98 g/cm3, a Mohs hardness of 9 and a melting point of 2040 °C. The chromium is what makes it a laser: the datasheet lists pump and tuning ranges, and a ruby laser was used for lunar ranging from Earth in 1969.
Where it's used
Laser rods
CRYLINK sells ruby laser crystals for solid-state lasers, in diameters of 3 to 40 mm and lengths of 10 to 140 mm.
Lunar ranging, 1969
The Lick Observatory team used a 1.2 GW ruby-crystal laser to range to the Apollo 11 retroreflector on 1 August 1969. The IEEE milestone page calls it the first Earth-to-Moon distance measurement with centimetre accuracy.
McDonald lunar-ranging station
NASA's station description says the McDonald 2.7-m telescope uses pulsed ruby laser light for lunar ranging.
Bearings and probes
Machine Design says sapphire balls can be drilled for jeweled bearing rollers, and ruby balls are used in valves and probe tips. No flight bearing record for ruby was read.
Recipe
Al2O3 with a Cr3+ dopant (Cr:Al2O3)
Ruby is alumina grown as one crystal, with chromium (Cr3+) taking a small share of the metal sites in place of aluminium. CRYLINK gives the formula as Cr3+:Al2O3 and the growth method as Czochralski (CZ). Wikipedia says the dopant is around 0.05% of the crystal and is responsible for all of the absorption and emission, and that synthetic ruby is pink or red depending on the dopant concentration.
| Ingredient | Share of the weight | What it does |
|---|---|---|
| Aluminium oxide host lattice Al2O3 | not stated | The host crystal. The chromium sits in some of its metal sites. |
| Chromium Cr | not stated | Cr3+ activator ion. It causes the blue and green absorption bands and the laser emission. |
Weight shares are as printed in the sources.
What it can do
Hardness
Mohs 9
CRYLINK gives a Mohs hardness of 9 for ruby. No Vickers or fracture figure was read.
Heat
2040 °C
The melting point is 2040 °C and the specific heat is 761 J/(kg·K) at 18 °C, both from the CRYLINK datasheet.
Laser band
680 to 1100 nm
The tuning range is 680 to 1100 nm, and the pump range is 450 to 532 nm. The absorption coefficient at 510 nm is 0.5 to 2.5 per cm.
Pulse energy in 1969
1.2 GW
The Lick Observatory ruby-crystal laser was rated at 1.2 GW (IEEE milestone page). This is a ground instrument, not a space-rated one.
How it compares
Compared with undoped sapphire in sapphire.yaml, ruby has nearly the same density and melting point. The difference is the chromium: about 0.05% of the crystal, which gives the pink or red colour, the absorption bands and the laser action. Ruby's datasheet gives 35 W/(m·K) at 25 °C perpendicular to the c axis, while the Kyocera sheet cited in sapphire.yaml gives a higher figure at 20 °C. Those are different suppliers at different temperatures, so the gap is not a like-for-like test. Sapphire's profile gives a transmission range and radiation results that this profile does not have for ruby.
The same measurements for each material, so you can compare them. Each row names the key condition under the value; the full conditions and methods are in the numbered notes under Technical details. Other materials are shown beside it; each was measured under its own conditions, so open its page before comparing closely. Compare every grade in the family.
| Measurement | Cr:Al2O3 | Al2O3 | CaF2 | LiF | ZnSe | ZnS | CsI | CdSe | Be3Al2Si6O18 / SiO2 / CuAl6(PO4)4(OH)8 / KAlSi3O8 / (Mg,Fe)2SiO4 |
|---|---|---|---|---|---|---|---|---|---|
| Thermal behavior and safety | |||||||||
| Melting pointValue printed in a supplier datasheet | 2040 °C | 2040 to 2054 °C | 1360 °C | 848 °C | 1525 °C | 1827 °C | 621 °C | 1537 °C | no data |
| Specific heat capacity at 18 °C | 761 J/(kg·K)1 | 0.75 J/(g·K) | 854 J/(kg·K) | 1562 J/(kg·K) | 0.339 J/(g K) | 515 J/(kg·K) | 201 J/(kg·K) | 258 J/(kg × K) | no data |
| Thermal conductivity at 25 °C, perpendicular to the c axis | 0.35 W/(cm·K)2 | 42 W/(m·K) | 9.71 W/(m·K) | 11.3 W/(m·K) | 18 W m-1 K-1 | 27.2 W/(m·K) | 1.1 W/(m·K) | 6.9 W/(m × K) | no data |
| Thermal conductivity at 25 °C, parallel to the c axis | 0.33 W/(cm·K)3 | 42 W/(m·K) | 9.71 W/(m·K) | 11.3 W/(m·K) | 18 W m-1 K-1 | 27.2 W/(m·K) | 1.1 W/(m·K) | 6.9 W/(m × K) | no data |
| Physical and electrical | |||||||||
| Density, CZ-grown Cr:Al2O3Value printed in a supplier datasheet | 3.98 g/cm³ | 3.97 g/cm³ | 3.18 g/cc | 2.639 g/cc | 5.27 g/cm³ | 4.09 g/cm³ | 4.51 g/cc | 5.81 g/cm³ | 2.63 to 2.97 g/cm³ |
| Mohs hardnessValue printed in a supplier datasheet | 9 - | 9 - | no data | no data | no data | no data | no data | 3.25 - | 7.5 to 8 - |
| Other measurements | |||||||||
| Thermal expansion, perpendicular to the c axis, 20 to 100 °C | 4.78 ppm/K4 | 7.7 ppm/K | 18.85 ppm/K | 37 ppm/K | 7.1 x10-6/K | 6.5 ppm/K | 48.3 ppm/K | 2.45 x10-6/K | no data |
| Thermal expansion, parallel to the c axis, 20 to 100 °C | 5.31 ppm/K5 | 7.7 ppm/K | 18.85 ppm/K | 37 ppm/K | 7.1 x10-6/K | 6.5 ppm/K | 48.3 ppm/K | 2.45 x10-6/K | no data |
| Refractive index, npValue printed in a supplier datasheet | 1.759 - | 1.768 - | 1.399 - | 1.392 - | 2.403 - | 2.201 - | 1.739 - | 2.431 - | 1.567 to 1.61 - |
| Refractive index, nmValue printed in a supplier datasheet | 1.767 - | 1.768 - | 1.399 - | 1.392 - | 2.403 - | 2.201 - | 1.739 - | 2.431 - | 1.567 to 1.61 - |
| Birefringence | 0.0082 -6 | no data | no data | no data | no data | no data | no data | no data | no data |
| Laser tuning rangeRange printed in a supplier datasheet | 680 to 1100 nm | no data | no data | no data | no data | no data | no data | no data | no data |
| Pump wavelength rangeRange printed in a supplier datasheet | 450 to 532 nm | no data | no data | no data | no data | no data | no data | no data | no data |
| Absorption coefficient at 510 nmRange printed in a supplier datasheet | 0.5 to 2.5 cm-1 | no data | no data | no data | 5×10^-4 cm-1 | no data | no data | no data | no data |
Why choose it, and why not
Good for
- Pulsed and tunable laser rods, with a pump band of 450 to 532 nm and a tuning range of 680 to 1100 nm (CRYLINK).
- Hard, stiff optical and bearing parts where Mohs 9 is needed (CRYLINK for hardness, Machine Design for ball use).
- Ground lunar ranging, as the 1969 Lick and McDonald work showed (IEEE milestone, NASA station description).
Watch out for
- Space data is thin. No ruby radiation, outgassing or thermal-vacuum result was found, and the NASA items are ground or lunar-ranging records.
- Values come from one supplier. CRYLINK is the source for all physical properties, and the datasheet is undated.
- Orientation matters. The datasheet asks for 90 degrees to the c axis with less than 5 degrees of tolerance.
- Dopant level varies. The 0.05% figure is from Wikipedia, not from a rod datasheet, and early dark rods used a different chromium level.
Ruby is sapphire with a chromium dopant, and the dopant is what makes it a laser. Its datasheet gives hardness, density, a pump band and a tuning range. The space record is ground lunar ranging in 1969 and ball use in valves and probes, not flight hardware, so a ruby-specific radiation and outgassing check is needed before any space use.
Technical details
For scientists and researchers. Everything above comes from the record below: every number with its method, its conditions and its source.
Notes
The method, full conditions and any caveat for the numbered rows above.
| # | Measurement | Method | Conditions | Caveat |
|---|---|---|---|---|
| 1 | Specific heat capacity at 18 °C | Value printed in the datasheet as J kg-1 K-1; written in the same units | temperature 18 °C | — |
| 2 | Thermal conductivity at 25 °C, perpendicular to the c axis | Value printed in the datasheet as W cm-1 K-1 and kept in that unit; 0.35 W/(cm·K) equals 35 W/(m·K) | temperature 25 °Corientation perpendicular to the c axis | — |
| 3 | Thermal conductivity at 25 °C, parallel to the c axis | Value printed in the datasheet as W cm-1 K-1 and kept in that unit; 0.33 W/(cm·K) equals 33 W/(m·K) | temperature 25 °Corientation parallel to the c axis | — |
| 4 | Thermal expansion, perpendicular to the c axis, 20 to 100 °C | Printed as 4.78×10-6 K-1; 1 ppm/K equals 1×10-6 K-1 | temperature range 20 to 100 °Corientation perpendicular to the c axis | — |
| 5 | Thermal expansion, parallel to the c axis, 20 to 100 °C | Printed as 5.31×10-6 K-1; 1 ppm/K equals 1×10-6 K-1 | temperature range 20 to 100 °Corientation parallel to the c axis | — |
| 6 | Birefringence | Value printed in a supplier datasheet, under the name Double Refraction | wavelength not stated on the datasheet | — |
Risks and side effects
Hazards to people, what happens when a cell overheats, and how the material is handled and stored.
For people
The only hazard records read are PubChem's entries for chromium(III) oxide powder, which are minority notifications. They do not describe a solid ruby crystal.
- Minority classifications
- PubChem lists H302, H317, H319 and H360 for some chromium(III) oxide notifications, with signal word Danger. These concern powder, not a solid crystal.
- Datasheet
- The CRYLINK datasheet has no safety section.
If it fails
The failure information comes from the supplier datasheet and from NASA-era records. No flight failure was read.
- Orientation
- The datasheet sets the orientation tolerance below 5 degrees, so a rod cut outside it does not match the specification.
- Wavelength band
- The datasheet gives a pump band of 450 to 532 nm and a tuning range of 680 to 1100 nm. Light outside these bands is outside the specification.
Handling and storage
- Protective equipment
- No ruby-specific guidance was read. The chromium(III) oxide record gives precautionary codes but not their text.
- Not covered
- No storage or handling limit for ruby was read in this run.
Test details
The original wording and numbers from the sources, for readers who want them.
Failure risks
| Failure | Trigger and consequence |
|---|---|
| Misaligned crystal orientationlow severity | A rod cut or mounted outside the datasheet orientation toleranceThe datasheet sets the orientation at 90 degrees to the c axis with a tolerance below 5 degrees, so a rod outside that tolerance does not match the sold specification. |
| Light outside the specified pump or tuning bandmoderate severity | Pump light outside 450 to 532 nm, or laser output outside 680 to 1100 nmThe datasheet gives absorption of 0.5 to 2.5 per cm at 510 nm and specifies pump and tuning ranges only. Operation outside those bands is outside the supplier's specification. |
Handling and storage
- The datasheet has no handling or storage section, and no fracture, handling or storage figure for ruby was read in this run.
Mitigations
- Specify the orientation and its tolerance when ordering. The datasheet gives an orientation tolerance below 5 degrees and an orientation of 90 degrees to the c axis.
Supply and geography
How common the raw materials are and where they come from.
Alumina feedstock for ruby (world alumina production, 2025 estimate)
- Top producers (2025)
- China 62%, Australia 11.3%, Brazil 7.3%, India 5.5%
- Recycling
- USGS: Recycling: None (bauxite and alumina chapter).
- Substitutes
- USGS names silicon carbide and alumina zirconia as substitutes in some abrasive and refractory uses. The chapter names no substitute for alumina used in single-crystal growth.
Chromium dopant (chromium mine production, 2025 estimate)
- Top producers (2025)
- South Africa 45.1%, Turkey 17.6%, Kazakhstan 13.7%, India 5.9%
- Recycling
- USGS: In 2025, recycled chromium contained in reported stainless-steel scrap receipts accounted for 21% of apparent consumption.
- Substitutes
- USGS: chromium has no substitute in stainless steel or in superalloys. The chapter does not discuss its use as a laser dopant.
Documents
Datasheets, safety data sheets, papers and standards you can open.
Full record
The complete spore, as stored. Free to reuse under CC-BY-4.0. Images keep the licence shown with each one.
Show the full YAML
spore: profile
id: ruby
spore_version: 0.2
family: optical-crystals
name: Ruby (chromium-doped single-crystal alumina)
abbreviation: Cr:Al2O3
role: solid-state laser crystal, optical window and jewel bearing material
category: glasses-optics
type: optical-crystals
summary: |
Ruby is alumina (Al2O3) grown as one crystal with a small amount of chromium (Cr3+) in place of aluminium. The laser-crystal supplier CRYLINK grows it by the Czochralski method and gives a density of 3.98 g/cm3, a Mohs hardness of 9 and a melting point of 2040 °C. Its datasheet lists a pump band of 450 to 532 nm and a tuning range of 680 to 1100 nm, which is what the chromium adds: it turns the crystal into a laser medium. In 1969 a ruby laser at Lick Observatory ranged to the Apollo 11 retroreflector, and NASA later used pulsed ruby light at a McDonald Observatory lunar-ranging station. Most values come from one supplier datasheet, so each value is kept with its own source.
best_for: Pulsed and tunable solid-state laser rods that need a hard, well-characterised crystal with a known pump band
weakest_at: 'Little space-qualification data: the sources read cover ground lasers, lunar ranging from Earth and one datasheet, with no ruby-specific radiation, outgassing or thermal-vacuum result'
identity:
formula: Al2O3 with a Cr3+ dopant (Cr:Al2O3)
crystal_system: trigonal (CRYLINK lists the crystal system as trigonal, with hexagonal axes a = 4.748 Å and c = 12.957 Å)
source: crylink-ruby
where: BASIC PARAMETERS table, Chemical Formula, Crystal System and Lattice Constant rows
tags:
environments: []
stresses: []
applications:
- optics-and-cameras
- mechanisms
properties:
- benchmark: density
label: Density, CZ-grown Cr:Al2O3
value: 3.98
unit: g/cm3
scope: material
conditions:
form: single crystal, Czochralski grown
temperature: not stated
method: Value printed in a supplier datasheet
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Density (g/cm3) row
- benchmark: mohs_hardness
label: Mohs hardness
value: 9
unit: '-'
scope: material
conditions:
scale: Mohs
method: Value printed in a supplier datasheet
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Mohs Hardness row
- benchmark: melting_point
label: Melting point
value: 2040
unit: °C
scope: material
conditions:
form: single crystal, Czochralski grown
method: Value printed in a supplier datasheet
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Melting Point row
- benchmark: specific_heat
label: Specific heat capacity at 18 °C
value: 761
unit: J/(kg·K)
scope: material
conditions:
temperature: 18 °C
method: Value printed in the datasheet as J kg-1 K-1; written in the same units
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Specific Heat Capacity @18°C row
- benchmark: thermal_conductivity
label: Thermal conductivity at 25 °C, perpendicular to the c axis
value: 0.35
unit: W/(cm·K)
scope: material
conditions:
temperature: 25 °C
orientation: perpendicular to the c axis
method: Value printed in the datasheet as W cm-1 K-1 and kept in that unit; 0.35 W/(cm·K) equals 35 W/(m·K)
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Thermal Conductivity @25°C, Perpendicular to the C axis row
- benchmark: thermal_conductivity
label: Thermal conductivity at 25 °C, parallel to the c axis
value: 0.33
unit: W/(cm·K)
scope: material
conditions:
temperature: 25 °C
orientation: parallel to the c axis
method: Value printed in the datasheet as W cm-1 K-1 and kept in that unit; 0.33 W/(cm·K) equals 33 W/(m·K)
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Thermal Conductivity @25°C, Parallel to the C axis row
- benchmark: cte
label: Thermal expansion, perpendicular to the c axis, 20 to 100 °C
value: 4.78
unit: ppm/K
scope: material
conditions:
temperature_range: 20 to 100 °C
orientation: perpendicular to the c axis
method: Printed as 4.78×10-6 K-1; 1 ppm/K equals 1×10-6 K-1
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Thermal Expansivity (20 – 100°C), Perpendicular to the C axis row
- benchmark: cte
label: Thermal expansion, parallel to the c axis, 20 to 100 °C
value: 5.31
unit: ppm/K
scope: material
conditions:
temperature_range: 20 to 100 °C
orientation: parallel to the c axis
method: Printed as 5.31×10-6 K-1; 1 ppm/K equals 1×10-6 K-1
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Thermal Expansivity (20 – 100°C), Parallel to the C axis row
- benchmark: refractive_index
label: Refractive index, np
value: 1.759
unit: '-'
scope: material
conditions:
wavelength: not stated on the datasheet
label: np
method: Value printed in a supplier datasheet
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Refractive Index row (np = 1.759)
- benchmark: refractive_index
label: Refractive index, nm
value: 1.767
unit: '-'
scope: material
conditions:
wavelength: not stated on the datasheet
label: nm
method: Value printed in a supplier datasheet
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Refractive Index row (nm = 1.767)
- benchmark: birefringence
label: Birefringence
value: 0.0082
unit: '-'
scope: material
conditions:
wavelength: not stated on the datasheet
method: Value printed in a supplier datasheet, under the name Double Refraction
status: ground
source: crylink-ruby
where: BASIC PARAMETERS table, Double Refraction row
- benchmark: laser_tuning_range
label: Laser tuning range
value: 680
value_high: 1100
bound: range
unit: nm
scope: material
conditions:
use: solid-state laser output, Cr3+:Al2O3
method: Range printed in a supplier datasheet
status: ground
source: crylink-ruby
where: PARAMETERS table, Tuning Range (nm) row (680 – 1100)
- benchmark: pump_wavelength_range
label: Pump wavelength range
value: 450
value_high: 532
bound: range
unit: nm
scope: material
conditions:
use: optical pumping of Cr3+:Al2O3
method: Range printed in a supplier datasheet
status: ground
source: crylink-ruby
where: PARAMETERS table, Pumping Range (nm) row (450 – 532)
- benchmark: absorption_coefficient
label: Absorption coefficient at 510 nm
value: 0.5
value_high: 2.5
bound: range
unit: cm-1
scope: material
conditions:
wavelength: 510 nm
method: Range printed in a supplier datasheet
status: ground
source: crylink-ruby
where: PARAMETERS table, Absorption Coefficient @510 nm (cm-1) row (0.5 – 2.5)
corrosion: []
risks:
hazards:
- text: PubChem's record for chromium(III) oxide, Cr2O3, says it does not meet GHS hazard criteria for 57.8% (1112 of 1924) of reports. The minority classifications are H302 (24%), H317 (25.7%), H319 (24.3%) and H360 (14.6%), with signal word Danger. These describe the oxide powder, not a sealed or solid ruby crystal.
ghs:
- H302
- H317
- H319
- H360
source: pubchem-cr2o3
where: Safety and Hazards, GHS Classification (CID 517277, chromia)
- text: The CRYLINK datasheet has no safety or handling section. No safety data sheet for a ruby crystal was read in this run.
ghs: []
source: crylink-ruby
where: Whole datasheet (no safety section)
failure_risks:
- mode: Misaligned crystal orientation
trigger: A rod cut or mounted outside the datasheet orientation tolerance
consequence: The datasheet sets the orientation at 90 degrees to the c axis with a tolerance below 5 degrees, so a rod outside that tolerance does not match the sold specification.
severity: low
source: crylink-ruby
where: PARAMETERS table, Orientation and Orientation Tolerance rows
- mode: Light outside the specified pump or tuning band
trigger: Pump light outside 450 to 532 nm, or laser output outside 680 to 1100 nm
consequence: The datasheet gives absorption of 0.5 to 2.5 per cm at 510 nm and specifies pump and tuning ranges only. Operation outside those bands is outside the supplier's specification.
severity: moderate
source: crylink-ruby
where: PARAMETERS table, Pumping Range, Tuning Range and Absorption Coefficient rows
side_effects: []
handling:
- text: The datasheet has no handling or storage section, and no fracture, handling or storage figure for ruby was read in this run.
source: crylink-ruby
where: Whole datasheet (no handling section)
mitigations:
- text: Specify the orientation and its tolerance when ordering. The datasheet gives an orientation tolerance below 5 degrees and an orientation of 90 degrees to the c axis.
source: crylink-ruby
where: PARAMETERS table, Orientation and Orientation Tolerance rows
uses:
- application: optics-and-cameras
device: Cr:Al2O3 laser rods for solid-state lasers
example: CRYLINK sells ruby laser crystals from 3 to 40 mm in diameter and 10 to 140 mm long, for solid-state lasers, optical glass and watch parts.
source: crylink-ruby
where: DESCRIPTION and APPLICATIONS sections; PARAMETERS table, Dia and Length rows
- application: optics-and-cameras
device: Pulsed ruby laser ranging to the Apollo 11 retroreflector (Lick Observatory, 1969)
example: On 1 August 1969 the Lick Observatory team fired a 1.2 GW ruby-crystal laser at the Apollo 11 retroreflector array and measured the round-trip time of the returning pulse.
source: ieee-lure
where: Milestone text, first paragraph; quote from Hal Walker, Jr.
- application: optics-and-cameras
device: Pulsed ruby laser lunar-ranging station at McDonald Observatory (2.7 m telescope)
example: NASA's station description says the McDonald 2.7-m telescope transmits and receives pulsed ruby laser light for lunar ranging, in three 45-minute daily runs about three weeks a month.
source: nasa1973
where: Abstract (description of the lunar ranging station at McDonald Observatory)
- application: mechanisms
device: Jewel bearing rollers from drilled sapphire balls, and ruby balls in valves and probe tips
example: Machine Design says sapphire balls can be drilled for use as precision jeweled bearing rollers for low-friction, long-wear use, and that ruby balls are used in chemical pump-check valves, wind indicators and probe tips.
source: machinedesign
where: Uses and Bearings section
supply:
- subject: Alumina feedstock for ruby (world alumina production, 2025 estimate)
producers:
- country: China
share_percent: 62
year: 2025
- country: Australia
share_percent: 11.3
year: 2025
- country: Brazil
share_percent: 7.3
year: 2025
- country: India
share_percent: 5.5
year: 2025
critical_lists: []
recycling: 'USGS: Recycling: None (bauxite and alumina chapter).'
substitutes:
- USGS names silicon carbide and alumina zirconia as substitutes in some abrasive and refractory uses. The chapter names no substitute for alumina used in single-crystal growth.
source: usgs-mcs2026-bauxite
where: World Alumina Refinery and Bauxite Mine Production table, alumina 2025e (world total 150,000 thousand t; China 93,000, Australia 17,000, Brazil 11,000, India 8,200). Shares calculated by Space Mushroom from these values. The chapter does not give ruby output.
- subject: Chromium dopant (chromium mine production, 2025 estimate)
producers:
- country: South Africa
share_percent: 45.1
year: 2025
- country: Turkey
share_percent: 17.6
year: 2025
- country: Kazakhstan
share_percent: 13.7
year: 2025
- country: India
share_percent: 5.9
year: 2025
critical_lists: []
recycling: 'USGS: In 2025, recycled chromium contained in reported stainless-steel scrap receipts accounted for 21% of apparent consumption.'
substitutes:
- 'USGS: chromium has no substitute in stainless steel or in superalloys. The chapter does not discuss its use as a laser dopant.'
source: usgs-mcs2026-chromium
where: World Mine Production and Reserves table, 2025e column (world total 51,000 thousand t, chromium content). Shares calculated by Space Mushroom from these values. Recycling and Substitutes paragraphs.
documents:
- title: 'CRYLINK: Laser crystal Cr:Al2O3 (ruby) datasheet, two versions read (values agree)'
type: datasheet
url: https://www.laser-crylink.com/wp-content/uploads/CrAL2O3-Crylink.pdf
year: 2026
- title: 'USGS Mineral Commodity Summaries 2026: Chromium'
type: report
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
year: 2026
- title: 'USGS Mineral Commodity Summaries 2026: Bauxite and Alumina'
type: report
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bauxite-alumina.pdf
year: 2026
- title: 'PubChem: Chromia (chromium(III) oxide, CID 517277), GHS classification summary, pug_view record'
type: database
url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/517277/JSON
year: 2026
- title: 'NASA grant NsG-331: Exchange-coupled chromium ion pairs in ruby (L. F. Mollenauer, Stanford report 1329, May 1965)'
type: report
url: https://ntrs.nasa.gov/citations/19660030055
year: 1965
- title: 'NASA Technical Reports Server: A description of the lunar ranging station at McDonald Observatory'
type: report
url: https://ntrs.nasa.gov/citations/19730027447
year: 1973
- title: 'IEEE Milestone: Apollo 11 Lunar Ranging Experiment (LURE), 1969'
type: report
url: https://ieeemilestones.ethw.org/Milestones:Apollo_11_Lunar_Ranging_Experiment_(LURE)
year: 2019
- title: 'Machine Design: Synthetic sapphire and ruby for precision uses (trade article)'
type: report
url: https://www.machinedesign.com/archive/article/21821174/synthetic-sapphire-ruby-for-precision-uses
year: 2026
gaps:
- No ruby-specific flight, vacuum, outgassing, atomic-oxygen or radiation-ageing result was found in a source opened in this run. The space-related records are a 1965 spectroscopy report (NASA grant NsG-331), a NASA lunar-ranging station description and a 1969 ground ranging test.
- 'No ruby mechanical data beyond Mohs hardness were read: no Vickers or Knoop hardness, flexural or tensile strength, fracture toughness, elastic modulus or Poisson ratio for ruby.'
- Birefringence has no wavelength on the datasheet and no canonical property name; it is kept as birefringence.
- Laser tuning range, pump wavelength range and absorption coefficient are not canonical property names; snake_case names are used for them.
- The datasheet does not state the wavelength for the refractive index values or what the labels np and nm mean beyond the printed labels.
- The chromium level in commercial laser rods was not read from a datasheet. Wikipedia gives around 0.05% of the crystal, used here for composition only. The 1965 NASA report quotes a Cr2O3 concentration for an early dark ruby rod, but the text copy prints the percent sign as a garbled character, so that figure is not used as a value.
- Atomic weights of Al, O and Cr are not entered, because no source read in this run gives them.
- No corrosion, etching, water or humidity data for ruby was found. The sapphire wet-etch paper concerns undoped sapphire and is not used here.
- No ruby-specific safety data sheet was read. The PubChem record covers chromium(III) oxide notifications, not a ruby crystal, and no dust exposure limit for ruby was found.
- No storage conditions or handling limits for ruby crystals were found.
- No ruby crystal production output or grower country shares were found. Supply uses USGS alumina production and chromium mine production as feedstock figures, not ruby output. The critical-mineral status of chromium was not checked against the 2025 list.
- 'No standard grade designations (UNS, EN, DIN, JIS) were applied: none of the sources read prints one for ruby.'
- The space bearing use is not sourced. The 2021 MDPI paper on sapphire jewel bearings for space magnetic suspension returned HTTP 403 and was not read. The bearing use here is the Machine Design article, which covers sapphire balls and ruby balls, not flight hardware.
- The 694.3 nm ruby laser line appears in Wikipedia, which is used here for composition only, so it is not entered as a property. No NASA or supplier value for the line was read in this run.
- A Crystran ruby page was not found in search. The Northrop Grumman laser crystal page did not render text in this run.
- The CRYLINK datasheet is undated; its year is the access year (2026). Two versions of the datasheet were read and their values agree.
- The Machine Design text was read through a summarising fetch tool, so its quotes are extracts rather than a raw copy of the page.
- The 1 August 1969 date and the 1.2 GW laser power come from one IEEE milestone page and are not checked against a second source.
- 'No media entries were added: no ruby images were read in this run.'
sources:
crylink-ruby:
title: 'CRYLINK: Laser crystal Cr:Al2O3 (ruby), basic parameters and spectra datasheet'
id: CrAL2O3-Crylink.pdf (undated)
url: https://www.laser-crylink.com/wp-content/uploads/CrAL2O3-Crylink.pdf
year: 2026
kind: datasheet
license: supplier document, linked not reproduced
usgs-mcs2026-chromium:
title: 'USGS Mineral Commodity Summaries 2026: Chromium'
id: USGS MCS 2026, February 2026
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-chromium.pdf
year: 2026
kind: report
license: public domain (USGS)
usgs-mcs2026-bauxite:
title: 'USGS Mineral Commodity Summaries 2026: Bauxite and Alumina'
id: USGS MCS 2026, February 2026
url: https://pubs.usgs.gov/periodicals/mcs2026/mcs2026-bauxite-alumina.pdf
year: 2026
kind: report
license: public domain (USGS)
pubchem-cr2o3:
title: PubChem compound record, Chromia (CID 517277), GHS classification
id: CID 517277 (Cr2O3)
url: https://pubchem.ncbi.nlm.nih.gov/rest/pug_view/data/compound/517277/JSON
year: 2026
kind: database
license: public domain (NCBI)
nasa1966:
title: Exchange-coupled chromium ion pairs in ruby (L. F. Mollenauer, Stanford Microwave Laboratory report 1329, NASA grant NsG-331)
id: NTRS 19660030055; May 1965
url: https://ntrs.nasa.gov/citations/19660030055
year: 1965
kind: report
license: public domain (NASA)
nasa1973:
title: A description of the lunar ranging station at McDonald Observatory (NASA Technical Reports Server)
id: NTRS 19730027447
url: https://ntrs.nasa.gov/citations/19730027447
year: 1973
kind: report
license: public domain (NASA)
ieee-lure:
title: 'IEEE Milestone: Apollo 11 Lunar Ranging Experiment (LURE), 1969'
id: ethw.org milestone page (oldid 7773)
url: https://ieeemilestones.ethw.org/Milestones:Apollo_11_Lunar_Ranging_Experiment_(LURE)
year: 2019
kind: web
license: IEEE milestone page, linked not reproduced
machinedesign:
title: 'Machine Design: Synthetic sapphire and ruby for precision uses'
id: machinedesign.com article 21821174
url: https://www.machinedesign.com/archive/article/21821174/synthetic-sapphire-ruby-for-precision-uses
year: 2026
kind: web
license: trade article, linked not reproduced
wiki-ruby:
title: 'Wikipedia: Ruby laser (composition only)'
id: en.wikipedia.org/wiki/Ruby_laser
url: https://en.wikipedia.org/wiki/Ruby_laser
year: 2026
kind: web
license: CC BY-SA 4.0
license: CC-BY-4.0
updated: '2026-10-26'
review:
status: draft
method: assistant
checked_values: 14
unreachable: 1
caveats: 5
note: 'Written by an AI assistant on 2026-10-26 from pages and PDFs read in the same run. Caveats: all physical property values come from one supplier datasheet; the NASA 1965 report text is OCR-like and its dopant figure is not used; the Machine Design text came through a summarising fetch; the MDPI bearing paper returned HTTP 403; the dopant level is from Wikipedia.'
story:
recipe:
line: Ruby is alumina grown as one crystal, with chromium (Cr3+) taking a small share of the metal sites in place of aluminium. CRYLINK gives the formula as Cr3+:Al2O3 and the growth method as Czochralski (CZ). Wikipedia says the dopant is around 0.05% of the crystal and is responsible for all of the absorption and emission, and that synthetic ruby is pink or red depending on the dopant concentration.
parts:
- name: Aluminium oxide host lattice
symbol: Al2O3
share: the bulk of the crystal; atom counts and atomic weights not found in the sources opened
role: The host crystal. The chromium sits in some of its metal sites.
- name: Chromium
symbol: Cr
share: around 0.05% of the crystal (Wikipedia)
role: Cr3+ activator ion. It causes the blue and green absorption bands and the laser emission.
risk_groups:
- title: For people
level: 1
verdict: No ruby-specific safety sheet was read
lead: The only hazard records read are PubChem's entries for chromium(III) oxide powder, which are minority notifications. They do not describe a solid ruby crystal.
points:
- label: Minority classifications
line: PubChem lists H302, H317, H319 and H360 for some chromium(III) oxide notifications, with signal word Danger. These concern powder, not a solid crystal.
- label: Datasheet
line: The CRYLINK datasheet has no safety section.
- title: If it fails
lead: The failure information comes from the supplier datasheet and from NASA-era records. No flight failure was read.
points:
- label: Orientation
line: The datasheet sets the orientation tolerance below 5 degrees, so a rod cut outside it does not match the specification.
- label: Wavelength band
line: The datasheet gives a pump band of 450 to 532 nm and a tuning range of 680 to 1100 nm. Light outside these bands is outside the specification.
- title: Handling and storage
gap: No storage or handling limit for ruby was read in this run.
points:
- label: Protective equipment
line: No ruby-specific guidance was read. The chromium(III) oxide record gives precautionary codes but not their text.
why: 'Ruby is alumina with a chromium dopant. Its datasheet gives a density of 3.98 g/cm3, a Mohs hardness of 9 and a melting point of 2040 °C. The chromium is what makes it a laser: the datasheet lists pump and tuning ranges, and a ruby laser was used for lunar ranging from Earth in 1969.'
uses:
- where: Laser rods
line: CRYLINK sells ruby laser crystals for solid-state lasers, in diameters of 3 to 40 mm and lengths of 10 to 140 mm.
- where: Lunar ranging, 1969
line: The Lick Observatory team used a 1.2 GW ruby-crystal laser to range to the Apollo 11 retroreflector on 1 August 1969. The IEEE milestone page calls it the first Earth-to-Moon distance measurement with centimetre accuracy.
- where: McDonald lunar-ranging station
line: NASA's station description says the McDonald 2.7-m telescope uses pulsed ruby laser light for lunar ranging.
- where: Bearings and probes
line: Machine Design says sapphire balls can be drilled for jeweled bearing rollers, and ruby balls are used in valves and probe tips. No flight bearing record for ruby was read.
can_do:
- label: Hardness
value: Mohs 9
line: CRYLINK gives a Mohs hardness of 9 for ruby. No Vickers or fracture figure was read.
- label: Heat
value: 2040 °C
line: The melting point is 2040 °C and the specific heat is 761 J/(kg·K) at 18 °C, both from the CRYLINK datasheet.
- label: Laser band
value: 680 to 1100 nm
line: The tuning range is 680 to 1100 nm, and the pump range is 450 to 532 nm. The absorption coefficient at 510 nm is 0.5 to 2.5 per cm.
- label: Pulse energy in 1969
value: 1.2 GW
line: The Lick Observatory ruby-crystal laser was rated at 1.2 GW (IEEE milestone page). This is a ground instrument, not a space-rated one.
compare: 'Compared with undoped sapphire in sapphire.yaml, ruby has nearly the same density and melting point. The difference is the chromium: about 0.05% of the crystal, which gives the pink or red colour, the absorption bands and the laser action. Ruby''s datasheet gives 35 W/(m·K) at 25 °C perpendicular to the c axis, while the Kyocera sheet cited in sapphire.yaml gives a higher figure at 20 °C. Those are different suppliers at different temperatures, so the gap is not a like-for-like test. Sapphire''s profile gives a transmission range and radiation results that this profile does not have for ruby.'
compare_rows:
- label: Density
benchmark: density
- label: Heat conduction
benchmark: thermal_conductivity
- label: Thermal expansion
benchmark: cte
handling:
- No ruby-specific safety data sheet was read. Treat the crystal as a dust and sharp-edge hazard until a supplier sheet says otherwise.
- Ask the supplier for the orientation and its tolerance, which the datasheet gives as below 5 degrees for ordinary rods.
- The chromium(III) oxide powder record lists precautionary codes, but their text was not read; do not rely on it for a crystal.
good_for:
- Pulsed and tunable laser rods, with a pump band of 450 to 532 nm and a tuning range of 680 to 1100 nm (CRYLINK).
- Hard, stiff optical and bearing parts where Mohs 9 is needed (CRYLINK for hardness, Machine Design for ball use).
- Ground lunar ranging, as the 1969 Lick and McDonald work showed (IEEE milestone, NASA station description).
watch_out:
- Space data is thin. No ruby radiation, outgassing or thermal-vacuum result was found, and the NASA items are ground or lunar-ranging records.
- Values come from one supplier. CRYLINK is the source for all physical properties, and the datasheet is undated.
- Orientation matters. The datasheet asks for 90 degrees to the c axis with less than 5 degrees of tolerance.
- Dopant level varies. The 0.05% figure is from Wikipedia, not from a rod datasheet, and early dark rods used a different chromium level.
verdict: Ruby is sapphire with a chromium dopant, and the dopant is what makes it a laser. Its datasheet gives hardness, density, a pump band and a tuning range. The space record is ground lunar ranging in 1969 and ball use in valves and probes, not flight hardware, so a ruby-specific radiation and outgassing check is needed before any space use.
References
Every number above carries a reference number. Click one to see the source and where in it the value comes from.
| # | Source | Type | Year | Used for |
|---|---|---|---|---|
| CRYLINK: Laser crystal Cr:Al2O3 (ruby), basic parameters and spectra datasheet | datasheet | 2026 | 21 values | |
| USGS Mineral Commodity Summaries 2026: Chromium | report | 2026 | 1 value | |
| USGS Mineral Commodity Summaries 2026: Bauxite and Alumina | report | 2026 | 1 value | |
| PubChem compound record, Chromia (CID 517277), GHS classification | database | 2026 | 1 value | |
| Exchange-coupled chromium ion pairs in ruby (L. F. Mollenauer, Stanford Microwave Laboratory report 1329, NASA grant NsG-331) | report | 1965 | 0 values | |
| A description of the lunar ranging station at McDonald Observatory (NASA Technical Reports Server) | report | 1973 | 1 value | |
| IEEE Milestone: Apollo 11 Lunar Ranging Experiment (LURE), 1969 | web | 2019 | 1 value | |
| Machine Design: Synthetic sapphire and ruby for precision uses | web | 2026 | 1 value | |
| Wikipedia: Ruby laser (composition only) | web | 2026 | 0 values |