SESAMs are instrumental in the development and volume production of pulsed laser systems including fiber lasers, solid-state lasers, and semiconductor lasers operating in both mode-locked and Q-switched regimes. Our team of experts in both semiconductor technology and laser physics is ready to provide extensive consulting for your application, to ultimately provide you with a customized SESAM of optimal performance, long lifetime and repeatability for volume production.

RefleKron’s SESAM-designs rely on monolithic semiconductor structures fabricated by Molecular Beam Epitaxy (MBE) using GaAs, InP and GaSb ‒based material systems. The ability to engineer the properties of such a versatile material system enables the fabrication of monolithic semiconductor mirrors over a wavelength range of 620 nm to 3.5 µm.

Wavelengths supported by our GaAs, InP and GaSb -based customized SESAMs.

Contact us to discuss the requirements of your application.

Every laser needs a unique SESAM

An often heard misconception regarding SESAMs is that they are unreliable, suffer from poor lifetimes and are not repeatable. These claims can be true, if the SESAM is operated outside of its suitable parameter range. For example, if the SESAM is not sufficiently adapted to the laser architecture, unnecessarily high fluences may be needed to prevent the onset of Q-switching.

Our approach of customizing SESAMs for each laser allows them to be operated in an optimal working regime. This is the key to long lifetime. Moreover, our comprehensive understanding of process optimization and extensive experience in MBE-technology allow to attain a high wafer-to-wafer repeatability suitable for industrial volume production. We have repeatedly qualified SESAM product lines with lifetimes exceeding 10 000 hours and excellent wafer-to-wafer repeatability ensuring volume production.

Tailored SESAM parameters

Freedom in the material selection provides additional advantages to the absorber layer and cavity design. Thus, the nonlinearity and saturation properties of the SESAM can be accurately tailored to specific laser systems independent on the wavelength range. The nonlinear absorption can be varied from below 0.5% to over 90%, while the saturation fluences range from 10 µJ/cm2 to above 100 µJ/cm2.

Linear reflectivity of a 640 nm SESAM used to mode-lock a red praseodymium laser, publication [7].
Linear reflectivity curves of resonant and antiresonant 2 µm SESAMs used to mode-lock a fiber laser, publication [4].

Perhaps the most important parameter in terms of repeatability for SESAMs, which is instrumental for volume production, is the relaxation time. We have extensive expertise in engineering the defect density in the absorber to gain control of the absorption recovery dynamics of the SESAM. The relaxation time can be customized from sub-ps to ns range to fit the specific application. A particular case is represented by the GaSb-based SESAMs operating at 2 µm and beyond, which have fast recombination dynamics with a sub-ps relaxation time component.

Table 1. General reference parameters for SESAMs to achieve mode-locked or Q-switched operation.


Selection of publications using RefleKron SESAMs

  1. Song, D.H., et al. “Spectrally combined four-diode-pumped femtosecond Ti:sapphire laser with 16.3 nJ pulse and its application to video-rate coherent anti-Stokes Raman scattering spectro-microscopy,” Opt. Express 31, 3269-3277, (2023)
  2. Yao, W., et al. “8.7-W average power, in-band pumped femtosecond Ho:CALGO laser at 2.1 µm,” Opt. Express 30, 41075-41083, (2022)
  3. Song, D.H., et al. “Spectrally combined three-diode-pumped compact femtosecond Ti:sapphire laser exceeding 1 W mode-locked power,” Opt. Express 29, 32649-32657, (2021)
  4. Koivusalo, E., et al. “2 µm High Power Short Pulse Laser Based on Monolithic Semiconductor Saturable Absorber” Public deliverable for the EU-ATTRACT Final Conference, (2020)
  5. Kajikawa, S., et al. “Visible ns-pulse laser oscillation in Pr-doped double-clad structured waterproof fluoride glass fibre with SESAM.” The Journal of Engineering, 2017: 407-409, (2017)
  6. Orsila, L., et al. “Ultrahigh precision nonlinear reflectivity measurement system for saturable absorber mirrors with self-referenced fluence characterization,” Opt. Lett. 39, 4384-4387, (2014)
  7. Gaponenko, M., et al. “SESAM mode-locked red praseodymium laser,” Opt. Lett. 39, 6939-6941, (2014)
  8. Koskinen, R., et al. “Highly nonlinear GaSb-based saturable absorber mirrors”, Proc. SPIE 7354, Nonlinear Optics and Applications III, 73540G, (2009)
  9. Wang, J., et al. “LD-Pumped Watt-level SESAM Passively Q-switched Alexandrite Laser”, IEEE Photonics Technology Letters 35, iss. 5, (2023)