High Power Laser Mirrors (Stocks)

In demanding laser systems with high power or high energies, laser mirrors must not only reflect efficiently but also remain stable under thermal and mechanical stress. Different lasers damage optics in different regimes. Continuous wave (CW) lasers tend to overheat the optics and cause damage, while pulsed lasers, depending on the pulse length, mainly cause dielectric breakdown. The laser mirrors must survive these damages. That’s where high power laser mirrors are needed. High power laser mirrors provide high laser induced damage threshold (LIDTs), ensuring precise beam steering where reliable, durable laser operation and minimal distortion are essential. The mirrors are essential for laser systems used for micro-machining, laser material processing, optical communication, and medical laser procedures etc.

Hangzhou Shalom EO provides a wide selection of off-the-shelf and custom high-power laser mirrors made of high reflection multi-layer dielectric coatings deposited on UV fused silica substrates. UV fused silica (UVFS) glass is an optical material renowned for its low thermal expansion and excellent optical clarity. The optical coatings are fabricated utilizing our IAD e-beam coating techniques, by introducing a low-energy ion beam during the deposition process, IAD promotes dense film growth and strengthens the mechanical bonding between film and substrate. This enables our mirrors to withstand intense laser fluences and resist thermal or mechanical stress commonly seen in pulsed and CW laser systems. All the laser mirrors undergo strict surface quality testing and laser damage threshold evaluation.

The optical thin film coating process is a complex process of substrate cleaning, coating material selection, and the final coating procedure. In Shalom EO's factories, we utilize SHINCRON MIC-1350TBN coating machine to manufacture our optical coatings, and the coating performances are inspected using PerkinElmer Lambda 1050+ spectrometer and Ultrafast Innovations GOBI white light interferometer.

Figure 1. and figure 2. SHINCRON MIC-1350TBN coating machine and PerkinElmer Lambda 1050+ spectrometer

Our high-reflective (HR) laser mirrors are designed to withstand high laser energies, and the mirrors are optimized to be used at 0° or 45° angle of incidence (AOI).

Multiple types of high LIDT laser mirrors are available in Shalom EO:

1. laser line dielectric mirrors offering laser induced damage threshold of >20J/cm2@1064nm,10ns, 10Hz, or 8J/cm2@532nm, 10ns, 10Hz, suitable for both continuous wave (CW) laser systems or pulsed laser systems. High reflectivity of >99.8% can be achieved. Various laser-specific wavelengths catering to applications of different laser systems are accessible; the standard wavelengths include multiple laser-specific options and the harmonic-generated wavelengths:

Nd:YAG high power laser mirrors: 266nm, 355nm, 532nm, 1064nm:

HeNe high power laser mirrors: 633nm

Alexandrite high power laser mirrors: 755nm

Ti:Sapphire high power laser mirrors: 800nm

Diode laser high power mirrors: 780nm, 808nm, 980nm

Other laser wavelengths: 400nm, 1310nm

2. Low GDD dielectric mirrors optimized for femtosecond pulsed lasers, these mirrors have minimized group delay dispersion (GDD) of ±20fs2 to prevent temporal stretching and dropping of the peaking power, at the same time, Shalom EO’s low GDD dielectric mirrors also have high reflectivity of >99.9%, and high laser damage thresholds of maximum 3J/cm2@800nm, 100ps, 100Hz or 4J/cm2@1030nm, 200ps, 100Hz engineered for extreme laser fluence.

3. Other special high power laser mirror types, such as:

Partially reflective laser out coupler: highest LIDT available: 15/cm2@1064nm, 10ns, 10Hz or 5J/cm2@532nm, 10ns, 10Hz

Dichroic Laser Mirrors:  15/cm2@1064nm, 10ns, 10Hz or 5J/cm2@532nm, 10ns, 10Hz

Application Notes:

1. What is laser induced damage threshold of an optic, and how can users compare this parameter to their laser systems?

A quick introduction, the laser induced damage threshold (LIDT) is defined as the highest fluence or power density per unit area that an optic can withstand before it cracks, quantified in J/cm2 for pulsed lasers, or W/cm2 for Continuous Wave (CW) lasers, at given wavelengths, pulse durations, and repetition rates.

You should first calculate the fluence (if your system is a pulsed laser) or irradiance (if your system is a CW laser) of your laser system. The calculation formula is as follows:

Fluence (J/cm2) = Pulse Energy (J)/Beam Area (cm2)

Irradiance (W/cm2) = Laser Power (W)/Beam Area (cm2)

The calculation above is based on the presumption that your laser beam has a uniform intensity distribution (i.e., the beam is a flat top beam); if the beam is a Gaussian beam, you should double the value gained via the equations above.

And then you can compare the value with the mirror’s LIDT; if your laser’s fluence or irradiance is lower than the laser mirror’s damage threshold, the optic is safe to use. However, be careful that when comparing, if the mirror’s LIDT is tested at different wavelengths with your lasers (you might also need to consider different pulse durations for pulsed lasers), you can’t just use the simple comparison method stated above; you have to scale the LIDT of the optic first. 

Two general rules of thumb for scaling are:

For CW lasers:  Scaled LIDT of The Optic = LIDT of The Optic * (Your Laser Wavelength/LIDT Wavelength)

For pulsed lasers: 

- How to adjust wavelength: Scaled LIDT of The Optic = LIDT of The Optic * (Your Laser Wavelength/LIDT Wavelength)^1/2

- How to adjust pulse durations: Scaled LIDT of The Optic = LIDT of The Optic * (Your Pulse Length/LIDT Wavelength)^1/2

The calculations introduced above can only provide a basic reference and should not be regarded as accurate and solid results. In practice, the situation might be far more complex, as other factors such as the beam sizes and the pulse length can all affect the damaging regime of optics. Shalom EO’s engineers are there for you to provide advice and tech support.

2. Note that the reflectance of the laser mirrors are dependent on the polarization directions. Compared to p-polarization, s-polarization has broader reflection bandwidths and higher reflection rates. The reflection rate specified for our products is (p-polarization reflectance + s-polarization reflectance) / 2