LASEROPTIK has longterm experiences in coating on almost every type of substrate. Besides the standard glasses like Fused Silica, BK7, CaF2, MgF2 or other common types e.g. made by SCHOTT, CORNING or OHARA, we offer optimized coating designs and techniques, substrate handling and coating fixtures especially for:
Crystals, wafers and metals
LASEROPTIK has approved coating processes including pre- and after-treatment for a broad variety of laser and non-linear crystals e. g. common materials like BBO, BiBO, COB, CTA, LBO, LiNbO3, KDP, KGW, KTA, KTP, KYW, RTA, RTP, YAB, YAG, YAP, YLF, YVO4, sapphire, diamond and many others. Dedicated rimless fixtures are developed and built in our workshop. Coatings for wafers and similar materials (e. g. Ge, Si, SiC, GaAs) are also available. LASEROPTIK has a selection of coatings on metals like Fe, Cu, Al. All processes are optimized for best optical performance and highest adhesion.
In rather “cold” sputter processes like Ion Beam Sputtering (IBS) or Magnetron Sputtering (MS) naked or fully confectioned fibres can be coated for special purposes, e. g. to achieve extremely low reflectivities for AR coatings. For MS some metres of fibres can be hidden in the spacious drum. Even lower temperatures can be realised with IBS. Adapted fixturing is available for a wide range of fibres.
has modified a coating plant for dielectric coatings on large optics up to 700 mm in length or diameter with a superior spectral homogeneity over the diameter / length and high LIDT values. Dedicated manual as well as automated ultrasonic cleaning procedures are employed to guarantee an optimum cleanliness also on these extraordinary geometries.
Due to the large demand, LASEROPTIK
has added an additional coating system in 2010 in order to coat dimensions even up to 1000 mm in the future.
Glass cells / cuvettes have to be coated on up to five sides. They require specially designed substrate holders and optimized coatings.
With the experiences of the last 25 years, LASEROPTIK developed a technique to achieve a maximum clear aperture and reliable fixtures.
Approved tooling as well as pre- and after-treatment processes are developed for coatings on UHV windows. Standard holders for the most common sizes from CF16 up to CF200 are prepared. The usual shadow-effects from the metal-flange will be reduced as technically possible in order to coat the maximum of the optical surface. With respect to the highest admissible temperature, that the windows can withstand, an adapted coating process is employed.
Special applications require special techniques. LASEROPTIK is an experienced manufacturer of:
Coatings with highest LIDT
Extremely low loss laser optics
The average laser power for commonly used systems like Nd:YAG and excimer lasers keeps growing enormously what makes high demands on laser optics. From the very beginning in the early 1980s, LASEROPTIK has gained its reputation by developing and producing coatings for the steadily increasing laser performance. This includes all coating types and the major laser lines, both CW and pulsed. Regular LIDT tests are carried out mainly by the Laser Zentrum Hannover with its longterm experience in this field.
As an example for a HR 1064nm / 0°, LASEROPTIK guarantees 40 J/cm2 (10ns, single shot) for a standard system and 80 J/cm2 for a high power system. Based on customer feedback and own r+d effort, we follow certain strategies to improve these values. This includes the minimisation of intrinsic losses (absorption and scattering) and macroscopic imperfections such as defects. Further approaches include the optimisation of the coating design with respect to standing-wave electric field peaks or rugate filters made by IBS as an alternative design concept.
The best choice to achieve the highest LIDT is strongly depending on the individual laser power parameters. This is why LASEROPTIK cannot offer a ‚one fits all’, but experienced assistance to find a tailored solution out of our 4 deposition methods and well assorted variety of cultivated coating materials.
Coated optics with extremely low losses (i.e. absorption and scattering) are required for so called super mirrors in ring laser gyroscope assemblies or certain scientific applications. These mirrors also reveal a maximum reflectivity with R >99,998 % and total losses <10ppm.
LASEROPTIK has modified an IBS machine that is capable to produce coatings on superpolished substrates. The cleanliness of the machine and environment is maintained in a dedicated super-clean room, where also the extensive substrate pre- and after-treatment takes place. Measurement devices such as whitelight profilometers and high resolution mircroscopes (up to x1000) for the inspection procedures are in place. A custom built cavity ring down setup allows to determine the reflection with a precision up to four decimal places and to refer back to the losses.
The total back scattering (TSb, as refer to ISO 13696) of a super mirror at 633 nm taken from LASEROPTIK’s current production has been measured at the Fraunhofer Institute for Applied Optics and Precision Engineering in Jena and achieved a value of TSb = 1,1 ppm. At a typical absoption and rest transmission of together <15ppm this equals a reflectivity of at least 99,998% and gets very close to the perfect laser mirror with R = 100%.
The results have been confirmed by LASEROPTIK’s in-house cavity ringdown setup and scatter measurement. A critical condition for the above mentioned values is using super-polished substrates with a surface roughness <1Å rms. Their quality is inspected with a whitelight interferometer.
In various projects LASEROPTIK has developed coatings and optics for laser applications in space or airborne and proven their functionality. IAD and IBS coatings withstand extreme temperature ranges and working conditions required for airborne laser optics. Additionally magnetron sputtered coatings are even tested as resistant against gamma radiation for use in space. Environmental testing can be done by LASEROPTIK, as all relevant devices are available.
Coatings for harsh environments
As described in the section ‘spaceborne and airborne coatings’, IAD and sputtered coatings withstand hostile working conditions, such as extreme temperature ranges or high humidity.
Magnetron sputtered coatings have also tested resistant to several acids and other fluids in customer projects.
LASEROPTIK has a longtime experience in coatings in the Vacuum Ultraviolet (VUV) range (120-179 nm), especially for 157 nm. In this spectrum, losses mainly arise by reason of absorption of water and hydrocarbons. Therefore VUV-CaF2 substrates are used and a surface roughness of σRMS < 0,3 nm helps to decrease the losses for all coatings. We guarantee LIDT > 400 mJ/cm2 with 15 ns pulses for HR157 nm/0°. Our mirrors withstand 2,5 billion pulses at 10 mJ/cm2 without any detectable degradation as reported from a longterm test. The values for PR and AR coatings will be in the same range.
LASEROPTIK has one dedicated coating system for infrared coatings made with non-radioactive materials. Due to strict environmental regulations we do not use ThF4 but still cover a range of up to λ = 5 µm for reflecting systems and up to λ = 10,6 µm for antireflecting systems. Coatings are applied on various IR substrates such as Ge, Ba, ZnSe, Saphirre, CaF2 and others. Metal coatings for IR applications are also applied, please see the brief description in the next section.
Dispersive coatings / chirped mirrors
Metal coatings have a fair but very broad reflectivity over a certain wavelength range. LASEROPTIK
offers metal coatings such as Al, Cr, Au, Ag, Pt, mostly with protection layer or even enhanced, i.e. with an additional dielectric coating system.
Flatness optimised processes
As a critical requirement for the generation of ultrashort pulses (e.g. for femtosecond lasers), dispersive dielectric mirrors also called ‘chirped mirrors’ are needed to compensate the group-delay dispersion (GDD) as otherwise the different delays of various frequency components within a short pulse result in pulse broadening.
The dispersion management is highly depending on the design and a subnanometer manufacturing accuracy for chirped mirrors. At LASEROPTIK
, this precision is ensured by the sophisticated method of Ion Beam Sputtering (IBS) that is capable to control the deposition of a complex, custom tailored stack of many (n>70) non-quarterwave layers. The results are measured by spectrally resolved whitelight interferometry
and are used for the reengineering of the coating design.
In addition, LASEROPTIK also designs and produces dispersion-matched pairs of broadband chirped mirrors for even better GDD compensation.
LASEROPTIK has approved coating processes in place that lead to a reduced amount of stress in the coating and help to avoid unwanted (a)spherical effects for flat substrates.
Stress can also be compensated by a special coating on the rear surface. An in-situ interferometer is installed in one machine to monitor the development of stress.