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Laser Mirrors

Dielectric Multilayer Mirrors

We are providing various kinds of optical mirrors from single layer metal mirror to complicated multi layer dielectric thin-film mirrors.

Laser Mirrors

High Reflectance and Low Loss

Most laser mirrors are constructed by dielectric materials since their optical absorption is very low, which allows high performance for high power laser beams. The high specular reflectance is due to the constructive interference of reflected light from respective boundaries between high and low index materials (shown in the lower left figure). The asymptotic value for normal incidence (angle of incidence (AOI) = 0 °) , R, is written as follows: R ≅ 1 − 4(nm ∕ nH2) (nL /nH)2p, for the case (nL ∕ nH)p<<1, where nH, nL (<nH) and nm are the refractive index of high index film material, low index film material and the substrate, respectively. The design is “Glass | (H L)p H| Air”. The symbols H and L denote the quarter-wave optical thickness for high and low index materials, respectively. You can see that we have almost perfect reflectance in principle : R → 1 when p → ∞ . Here, we note the quality of boundaries, specifically their roughness, which is a detriment for actually obtaining its high reflectance, since the roughness causes optical loss due to scattering.

We have been producing multilayer mirrors by using ion-assisted deposition and ion beam sputtering methods, which are state-of-art processes to coat dense film with smooth surfaces and boundaries. The films are also free from spectral shift problems caused by humidity fluctuations.

Multi-function

In multilayer mirror design, there are many choices for degrees of freedom, i.e., materials, layer thicknesses and number of layers. So, other functions can be added to the conventional mirror by modifying the regular alternating design,(H L)p. We propose mirrors with multiple functions by combining basic design concepts, analytical calculations and powerful optimization methods from the latest software. In applications for ultrafast laser systems, phase property is also important for wide spectral range. We produce multilayer mirrors used for dispersion compensation, the so called chirped mirror, which has typically negative group delay dispersion (GDD), - ∂2φ / ∂ω2, where φ is the reflected phase of the mirror and ω is the angular frequency. Complex design technique and precise thickness control in the coating process are required.

Electric field (EF) in a multilayer mirror is also important in applications for high power laser systems, since strong EF intensity breaks down the mirror itself. In design, EF distribution is adjusted to resist high power laser beam through choice of the layers’ thickness.

Please see our products listed in the following pages.

For femtosecond lasers Broad Band Chirped Mirror with Negative GDD

Application : Pulse compensation of femtosecond laser beam
Feature : Wide band, Dispersion,Flat GDD (<0)

Dispersion compensation in wide wavelength is an important technology for obtaining an ultrashort pulse with the pulse width less than 10fs.

A dielectric multilayer mirror can be used for this purpose, if its reflective phase, φ , is properly adjusted to the intended system. For up-chirped pulse, negative group delay dispersion (GDD), - ∂ 2 φ / ∂ ω2, is required. We have designed two kinds of chirped mirrors, which cancel each other oscillation of GDD in order to obtain a nearly flat negative GDD as a function of wavelength. Some features of the mirrors are a constant negative GDD and high reflectance for wavelengths between 600nm-1000nm.

WavelengthAOIReflectanceGDDSizePart number
600-1000nm0°~ 5°≧98%-40fs2φ25.4 x 5tCGS-002505-10
φ30 x 5tCGS-003005-10
φ50 x 5tCGS-005005-10

*custom products are also available

For femtosecond lasers Broad Band Chirped Mirror with Negative GDD and TOD

Application : Pulse compensation of femtosecond laser beam
Feature : Wide band, Dispersion compensation up to 3rd order

For precise control of the pulse shape, higher order dispersion compensation is required. Since, in general, group velocity dispersion (GVD) of mediums is large at shorter wavelengths, larger negative GDD is expected for chirped mirrors. This chirped mirror has been designed to compensate for GVD up to the 3rd order dispersion (TOD), - ∂3 φ / ∂ ω3, where GDD<0 and TOD<0. By using these mirrors in combination with the mirrors listed in P5, pulses with wide spectral width broaden by self phase modulation are compressed to 6.2fs (almost Fourier transformation limit). Measured auto correlation is shown in the right graph.

WavelengthAOIReflectanceGDDSizePart number
600-1000nm0°~ 5°≧98%-75fs2(600nm) ~ -0fs2(1000nm) TOD=-127fs3(800nm)φ25.4 x 5tCTS-002505-10
φ30 x 5tCTS-003005-10
φ50 x 5tCTS-005005-10

*custom products are also available

For femtosecond lasers Chirped Mirror for 800nm The fundamental  of Ti-sapphire laser

Application : Pulse compensation of femtosecond laser beam
Feature : High reflectance

This chirped mirror is design for the dispersion compensation of up-chirped pulses with wavelengths around 800nm. Some features of this mirror are a constant negative GDD and high reflectance for wavelengths between 750nm-850nm. The mirror coated on the rectangular substrate is also listed, which will be helpful to obtain large amount of GDD by multiple reflections between two opposite mirrors.

WavelengthAOIReflectanceGDDSizePart number
750-850nm0°~ 5°≧99.5%-40fs2φ25.4 x 5tCTF-002505-10
φ30 x 5tCTF-003005-10
φ50 x 5tCTF-005005-10
□20x40x 5tCTF-204005-10

*custom products are also available

For femtosecond lasers Chirped Mirror for UV The second harmonics of Ti-sapphire laser

Application : Pulse compensation of UV femtosecond laser beam
Feature : High reflectance and dispersion compensation in UV region

Dispersion compensation is an important technology in the Ti-Sapphire laser systems. In the molecular science, there are many cases where the second harmonics of the ultrashort pulses are used. In these cases, careful attention is required for larger dispersion of the group velocity of medium in the ultraviolet (UV) region. With this in mind and through the collaboration with Hishikawa lab. of Nagoya University, this chirped mirror has been developed for the sake of the dispersion compensation in the UV region.

WavelengthAOIReflectanceGDDSizePart number
395-405nm0°~ 5°≧99.5%-50fs2φ25.4 x 5tCUV-002505-10
φ30 x 5tCUV-003005-10
φ50 x 5tCUV-005005-10
□20x40x 5tCUV-204005-10

*custom products are also available

For femtosecond lasers GTI Laser Mirror  GDD= ‐1000fs2

Application : Pulse compensation of femtosecond laser beam
Feature : Large group delay dispersion(GDD) and low optical loss

This Gires-Tournois-Interferometer (GTI) laser mirror is designed for the dispersion compensation of up-chirped pulses with wavelengths around 1030nm. The main features of this mirror are large negative GDD and low optical loss accomplished by the ion beam sputtering coating process.

This mirror has been applied for the Kerr lens mode-locked thin-disk ring oscillator, and has been contributed to generate femtosecond laser pulses with an intra cavity peak power beyond 100MW (*1)

(*1) A. Amani Eilanlou, Yasuo Nabekawa, Makoto Kuwata-Gonokami and Katsumi Midorikawa Japanese Journal of Applied Physics 53, 082701(2014)

WavelengthAOIReflectanceGDDSizePart number
1020-1040nm0°~ 5°≧99.5%-1000fs2
(±400fs2)
φ25.4 x 5tCG1-002505-10
φ30 x 5tCG1-003005-10
φ50 x 5tCG1-005005-10

For femtosecond lasers Low Dispersion Mirror

Application : Turning mirror for ultra short pulses
Feature : Low dispersion and high reflectance

Femtosecond pulses are easily broadened and lose their high intensity peak when they propagate in mediums or are reflected by standard multilayer mirrors. This leads to difficulty with utilizing the femtosecond pulses’high peak during use. This mirror is designed to reduce changes in pulse shape through reflection. The result is shown in the image to the right. The short pulse sustains the sharpness even after changing its propagating direction from this mirror. Energy loss can be reduced compared to that of metal mirrors.

WavelengthAOIReflectanceGDDSizePart number
700-900nm(s-pol.)
750-850nm(p-pol.)
45°≧99%(s-pol.)
≧97%(p-pol.)
0fs2 ±10fs2
(s-pol. 800±50nm)
0fs2 ±50fs2
(s-pol. 800±100nm)
0fs2 ±50fs2
(p-pol. 800±50nm)
φ25.4 x 5tLDF-002505-10
φ30 x 5tLDF-003005-10
φ50 x 5tLDF-005005-10

*custom products are also available

For high power lasers High Power Laser Mirror

Application : High power laser systems
Feature : High laser induced damage threshold

In high power laser systems, multilayer mirrors are required to have high laser induced damage threshold (LIDT), since damage to the mirrors prevents increasing the output energy of the system. To make a mirror’s LIDT high, our mirrors are designed by taking into account the distribution of the electric field (EF) formed by incident laser beams in the mirrors.

The right figure shows standing waves of EF in a mirror for 1064nm. The intensities are normalized by the intensity of incident waves. The standing waves originate in the interference between propagating waves and reflected waves from respective boundaries, where waves in orthogonal polarization states are independent of each other. In general, the intensities became large near the incident medium. It had been pointed out that if the strong intensity peaks are located at boundaries, the mirror is easily broken down by high powered laser beams(*1 *2).

For the sake of application for high power laser systems, our mirrors are optimized to shift the EF intensity peaks from boundaries (shown by vertical dotted line), keeping high reflectance for the wave.

(*1)B.E. Newman, S.R. Folty, L.J. Jolin and C.K. Carniglia, Laser Induced Damage in Optical Materials:1981”, NBS Spec. Publ.638, p.3 63

(*2) Y. Sato, M. Kobiyama, S. Kimura and S. Tamura: daikoshi kiho, 39-4, p156 (1988) (in Japanese)

WavelengthAOIReflectanceLIDT#(p-pol.)SizePart number
1064nm45°≧99%(s and p-pol.)134J/cm2φ25.4 x 5t
φ30 x 5t
φ50 x 5t
Listed on List
532nm121J/cm2
355nm47J/cm2
248nm5.8J/cm2

*custom products are also available

# Evaluation method: 1-on-1, pulse width: 8~10ns
The LIDT’s listed in the table are typical values (not guaranteed).

For high power lasers Dual Wavelength Mirror  for High Power Lasers

Application : Second harmonic generation, High power laser systems
Feature : High laser induced damage threshold for 1064nm and 532nm

Recently, two high-power laser beams with different wavelength are often used simultaneously in an optical system. For example, the laser beams are Nd:YAG fundamental wave (1064nm) and its second harmonic wave (532nm) generated by the wavelength conversion technique. The optics used in the system, such as multilayer mirrors and optical thin film filters, are expected to have complex spectral reflectance and/or transmittance as well as the resistance for high powered laser beams.

We propose dual wavelength mirror with high laser induced damage thresholds (LIDT) for both 1064nm and 532nm, where this mirror is designed by extending the conventional design method. The high LIDTs of this mirror have been confirmed experimentally by the Institute of Laser Technology.

Conditions(1-on-1)

SamplesThis mirrorStandard mirror*
Wave length1064nm532nm1064nm532nm
Pulse length11.8ns8.2ns11.8ns8.2ns
Spot size x208μm202μm316μm438μm
Spot size y373μm276μm430μm695μm
AOI0 deg

LIDT

 This mirrorStandard mirror*
1064nm112J/cm267J/cm2
532nm>180J/cm246J/cm2

* The “Standard mirror” ’s data are shown to compare the LIDT to this mirror’s LIDT. The both mirrors have been coated by the same coating process using same layer materials.

WavelengthAOIReflectanceLIDT*SizePart number
532nm/1064nm≧99%(1064nm)
≧99%(532nm)
112J/cm2(1064nm)
>180J/cm2(532nm)
φ25.4 x 5tHPD-002505-10
φ30 x 5tHPD-003005-10
φ50 x 5tHPD-005005-10

* The LIDT’s listed in the table are typical values (not guranteed).

For special application Ultra Broad Band Mirror

Application : Harmonics of Nd:YAG laser,gas laser,etc.,
Feature : High reflectance at wide AOI in wide wavelength

This mirror is constructed by dielectric materials with over 200 layers. Since the film quality is very high as a result of applying ion beam sputtering to the coating process, the optical loss is very low regardless of the film’s high thickness. The main feature of this mirror is to have high reflectance for wide wavelengths and a wide angle of incidence regardless of the polarization. This mirror will allow greater flexibility when constructing laser systems.

For reference, the spectral reflectance is compared to that of an Ag mirror and Al mirror in the right graph.

WavelengthAOIReflectanceSizePart number
350-1100nm0°- 50°≧98%φ25.4 x 5tBBM-002505-10
φ30 x 5tBBM-003005-10
φ50 x 5tBBM-005005-10

For special application Ultra High Reflectance Mirror

Application : Cavity ring down spectroscopy
Feature : High reflectance over 99.99%

This mirror has an extremely high reflectance of over 99.99% at 1064nm. Although a high reflectance of nearly 100% is possible theoretically, it is difficult to actually coat such mirrors. Special attention should be paid to the quality of coating materials and the substrate as well as the coating process.

We produce this mirror by using the ion beam sputtering method in the coating process. The right graph is an evaluation of the mirror by the cavity ring down method. From the fittings of light intensity leaking from the cavity constructed by these mirrors with plano and 1m concave surface, the geometric mean of the respective mirror’s reflectance is evaluated as R>99.99%.

WavelengthAOIReflectanceSizePart number
1064nm≧99.99%φ25.4 x 5t(Plano)UHR-002505-10
φ25.4 x 5t(1m concave)UHR-002505-20
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