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Low-GDD Ultrafast Mirrors for 700 - 930 nm







Application Idea

UM15-45A Ø1.5" Mirror
in a POLARIS-K15S4 Mount



  • Ideal for Ti:Sapphire Lasers
  • Designed for 700 - 930 nm
  • Group Delay Dispersion < 30 fs2
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Item # UM05-45A UM10-45A UM15-45A UM20-45A
Design Wavelength Range 700 - 930 nm
Diameter 1/2" 1" 1.5" 2"
Diameter Tolerance +0.00 / -0.10 mm
Minor Diameter 0.28" 0.57" 0.85" 1.13"
Major Diameter 0.4" 0.8" 1.2" 1.6"
Thickness 6.4 mm 9.5 mm 12.0 mm 12.0 mm
Thickness Tolerance ±0.20 mm ±0.10 mm
Reflectance Rs > 99% (700 - 930 nm)
Rp > 99% (730 - 870 nm)
Angle of Incidence 45°
Group Delay Dispersion |GDDs| < 30 fs² (700 - 930 nm)
|GDDp| < 30 fs² (730 - 870 nm)
Laser Induced
Damage Thresholdb
0.40 J/cm2 (800 nm, 52 fs FWHM, S-Pol, 1000 Pulses)
Substrate Fused Silica
Front Surface Flatnessc <λ/4 <λ/6 <λ/4 <λ/2
Front Surface Quality 15-5 Scratch-Dig 20-10 Scratch-Dig
Parallelism ≤3 arcmin ≤5 arcmin
Back Surface Polished Fine Ground
  • The clear aperture is >80% of the diameter. These values are provided for use at 45° AOI.
  • For ultrafast optics, the laser induced damage threshold (LIDT) is defined as the fluence (per pulse) that produces visible damage after a given number of pulses. LIDT values are not guaranteed in the ultrashort pulse regime. As such, they are provided as a service to customers.
  • At 632.8 nm Over Clear Aperture


  • Low Group Delay Dispersion: |GDD| < 30 fs2
  • Ideal for Pulses Shorter than 250 fs
  • Reflectance Greater than 99%
  • Sizes: Ø1/2", Ø1", Ø1.5", or Ø2"

Thorlabs' low group delay dispersion (GDD) mirrors feature a coating designed for high reflectance in the 700 nm - 930 nm wavelength range and use at a 45° angle of incidence (AOI). These mirrors are ideal for Ti:Sapphire femtosecond pulsed lasers where pulse broadening is a concern, as well as imaging applications such as two photon microscopy. They offer an ideal combination of greater than 99% reflectance and less than |30 fs2| GDD; for details, please see the Graphs tab.

These mirrors are available in four different diameters: Ø1/2", Ø1", Ø1.5", or Ø2". The Ø1.5" version is ideal for use with amplified Ti:Sapphire laser systems, as it provides more surface area than a Ø1" mirror for expanded high-power beams while providing a more compact footprint than a Ø2" mirror.

The edge of each optic is engraved with the item number and an arrowhead pointing to the coated surface. The back surface of the Ø1/2", Ø1", and Ø1.5" mirrors is polished so that the small percentage of light that leaks through the reflective coating may be used for applications such as power monitoring. The fine ground back surface of the Ø2" mirror is ideal for use with higher power lasers, as the light passing through the mirror will be diffusely scattered.

Our low-GDD coating offers the highest reflectance of any of our mirrors for the Ti:Sapphire wavelength range. For a general comparison of the performance of our low-GDD mirrors, ultrafast-enhanced silver mirrors, standard protected silver mirrors, and broadband dielectric mirrors, please see the Mirror Comparison tab.

In addition to the low-GDD mirrors here, Thorlabs also offers low-GDD mirrors for various other wavelength ranges. For our full selection of optics for ultrafast applications, please see the Ultrafast Optics tab.

The graph on the left below shows measured results of the reflectance as a function of wavelength for both s- and p-polarizations. The graph on the right shows theoretical results for the group delay dispersion and represents the designed performance of our 700 nm - 930 nm low GDD coating. Both plots are for 45° AOI.

Mirror Reflectance
Click to Enlarge

Click for Raw Data
The shaded region represents the specified wavelength range where the absolute RS > 99%. Please note that the reflectance outside of this specified region is typical and can vary from lot to lot, especially where the reflectance is fluctuating or sloped.
Mirror GDD
Click to Enlarge

Click for Raw Data
The shaded region represents the design wavelength range. The GDD values fluctuate rapidly outside of the specified wavelength range of 700 - 930 nm for s-polarized light.

This tab compares four of Thorlabs' coatings for the Ti:Sapphire wavelength range: our low-GDD dielectric coating for 700 - 930 nm, our ultrafast-enhanced silver coating, our standard protected silver coating, and our broadband dielectric -E02 coating.

Qualitative Comparison
Our Low-GDD Dielectric Coating and Ultrafast-Enhanced Silver Coating are specifically designed for femtosecond Ti:Sapphire lasers. The low-GDD dielectric coating provides the highest reflectance, making it suitable for laser cavities, while the ultrafast-enhanced silver coating provides slightly lower reflectance and a slightly broader wavelength range. Each offers low group delay dispersion of <|30 fs2| or better.

The Protected Silver Coating offers the widest spectral range and minimal dependence on the angle of incidence. However, its reflectance at typical Ti:Sapphire wavelengths is somewhat lower than our low-GDD dielectric and ultrafast-enhanced silver coatings.

Our -E02 Broadband Dielectric Mirror Coating has resonance structures within the dielectric coating layers. These structures cause ripples in the group delay dispersion and can furthermore vary strongly between coating runs. While these variations do not impact CW performance, when an ultrafast laser pulse hits such a mirror, the pulse is strongly distorted. Thorlabs' low-GDD dielectric coating and the dielectric overcoat on our ultrafast-enhanced silver mirrors are designed in such a way that there is no resonance inside the layers, thereby maintaining smooth dispersion and reflectance across the design wavelength range.

Specs Comparison
The table below summarizes the reflectance, spectral range, and group delay dispersion of the different coatings.

Mirror Coating Spectral Range Item # Suffix Reflectance Group Delay Dispersion
Low-GDD Dielectric Coating S-Pol: 700 - 930 nm
P-Pol: 730 - 870 nm
-45A Rs > 99%
Rp > 99%
Click for Plot S-Pol: <|30 fs2|
P-Pol: <|30 fs2|
Click for Plot
Ultrafast-Enhanced Silver Coating 750 - 1000 nm -AG Rs > 99.0%
Rp > 98.5%
Click for Plot S-Pol: <|20 fs2|
P-Pol: <|30 fs2|
Click for Plot
Protected Silver Coating 450 nm - 20 µm -P01 Ravg > 97.5% for 450 nm - 2 µm
Ravg > 96% for 2 - 20 µm
Click for Plot Not Specifieda,b -
-P02 Ravg > 97% for 450 nm - 2 µm
Ravg > 95% for 2 - 20 µm
Click for Plot Not Specifieda,b -
Broadband Dielectric Coating 400 - 750 nm -E02 Ravg > 99% Click for Plot Not Specifiedb -
  • While a bare silver coating has almost no dispersion, some silver mirrors have a dielectric coating which can increase the dispersion, especially when the dielectric coating is used to enhance spectral features. Our protected silver mirrors feature such a dielectric coating for protection of the fragile silver coating.
  • Our standard -P01, -P02, and -E02 coated mirrors are not specified for ultrafast applications, so we do not quantify their GDD from coating run to coating run. In contrast, our -45A and -AG coated mirrors are guaranteed to provide their specified GDD values.

Posted Comments:
Shaogang Yu  (posted 2020-08-25 11:24:26.863)
YLohia  (posted 2020-08-25 10:18:11.0)
Hello, thank you for contacting Thorlabs. An applications engineer from our team in China will contact you directly.
Brennan Peterson  (posted 2019-09-05 13:03:53.227)
Hello, Can you provide the coating type (IBS or ebeam) to understand the damage behavior.
YLohia  (posted 2019-09-05 02:35:59.0)
Hello, thank you for contacting Thorlabs. Most of our low dispersion mirror coatings, including the -45A, are IBS.
Volker Sonnenschein  (posted 2019-06-13 07:55:32.9)
How accurate is the Reflectance curve provided for these mirrors? As i doubt it is truly up to 99.996% as indicated in the excel sheet, i wonder how much absorption+scatter should be subtracted from the reflectivity value.
asundararaj  (posted 2019-06-22 11:16:01.0)
Thank you for contacting Thorlabs. The reflectance curves on the website are theoretical and don't account for absorption or scatter. We only specify 99% reflectance because we can confidently say that the coating has significantly less than 1% loss to scatter and absorption.
slm9  (posted 2014-08-22 11:23:26.39)
Dear Thorlabs-Team Do you have some specs for this coating if this mirror will be used under AOI 0°? I would like to know the spectral shift and the low GDD behavior @AOI 0°. Thanks and with best regards Markus
jlow  (posted 2014-09-18 02:07:45.0)
Response from Bweh at Thorlabs USA: We have theoretical plots for the reflectivity and GDD when used at 0 deg in comparison to 45 deg. Our European office will followup with you by email regarding this.
oliver.sandig  (posted 2014-06-08 11:48:35.417)
Hallo, ich suche ein Ultrafast-Spiegel der reflektierend für 800nm und transparent für 400nm ist, oder umgedreht. Können Sie mir dafür ein Spiegel empfehlen? Vielen Dank, Oliver Sandig
besembeson  (posted 2014-06-12 05:05:59.0)
A Response from Bweh at Thorlabs Newton-USA: Thanks for contacting Thorlabs. We don't carry such an ultrafast mirror at the moment that will reflect 400nm and transmit 800nm or vice versa. We do have dual band 400nm and 800nm high reflectivity ultrafast mirrors: ( I am curious about your application so I will contact you through our Germany office to find out more, and to determine if another stock item may work or if we have to look into a special coating for your application.
theresa.bruemmer  (posted 2014-02-10 10:52:39.893)
Do You have estimates on the damage threshold of these mirrors? Thanks, Theresa
besembeson  (posted 2014-02-12 03:59:33.0)
Response from Bweh E. at Thorlabs: Hi Theresa, These mirrors are ideal for Ti:Sapphire femtosecond pulsed lasers. The coating on this should withstand 1.5W of 800nm ultra-fast pulse with durations as short as 50fs, and 300mW of 400nm ultra-fast pulses with durations as short as 50fs. These numbers are based on a minimum laser beam diameter of about 1.2mm. Note that Pulsed lasers typically induce a different type of damage to the optic than CW lasers. Pulsed lasers often do not heat the optic enough to damage it; instead, pulsed lasers produce strong electric fields capable of inducing dielectric breakdown in the material (avalanche ionization). I will send you separate email requesting your laser characteristics to determine if this optic is suitable for your laser or not.
tcohen  (posted 2013-01-15 12:09:00.0)
Response from Tim at Thorlabs to Neil: Thank you for your feedback. I will send you measured data to supplement the calculated data provided on the “Graphs” tab. We will continue to update our presentation with more data.
steve.u.smith  (posted 2013-01-14 14:15:34.98)
Do you have the measured GDD curve to share to help me make a purchasing decision? Thanks Neil

Thorlabs offers a wide selection of optics optimized for use with femtosecond and picosecond laser pulses. Please see below for more information.

Based on your currency / country selection, your order will ship from Newton, New Jersey  
+1 Qty Docs Part Number - Universal Price Available
UM05-45A Support Documentation
UM05-45AØ1/2" Low-GDD Ultrafast Mirror, 700 nm - 930 nm, 45° AOI
UM10-45A Support Documentation
UM10-45AØ1" Low-GDD Ultrafast Mirror, 700 nm - 930 nm, 45° AOI
UM15-45A Support Documentation
UM15-45AØ1.5" Low-GDD Ultrafast Mirror, 700 nm - 930 nm, 45° AOI
UM20-45A Support Documentation
UM20-45AØ2" Low-GDD Ultrafast Mirror, 700 nm - 930 nm, 45° AOI
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