SAM – saturable absorber mirror

More documents

Recommendations

Info

The RSAM is a strong nonlinear optical device. The absorptance A of the absorber layer and the reflectance R of theRSAM depend on the incoming light intensity I. Due to the resonance condition of the Gires–Tournois interferometer atthe working wavelength the effective saturation intensity I sat,eff of the device shifts by a factor of about (π/F) 2 (F -finesse of the Gires–Tournois interferometer) to lower values in relation to the intrinsic material value I sat , which isvalid for non-resonant saturable absorber mirrors (SAM).The absorptance A of a RSAM with a not too small finesse F > 10 can be estimated byeq.(3)withΑ absorptanceA 0 small signal absorptance (saturable absorption)I light intensity (measured in W/m 2 )I sat intrinsic material saturation intensityF finesse of the RSAMThe effective saturation fluence Φ sat,eff of a RSAM can be estimated using the relaxation time τ and the effectivesaturation intensity I sat,effeq.(4)withΦ sat,effI sat,effτeffective saturation fluence of the RSAMeffective saturation intensity of the RSAMrelaxation time of the absorber materialWith typical values for a non-resonant SAM● I sat = 10 MW/cm 2●τ = 10 ps● Φ sat = 100 µJ/cm 2the relevant parameters for a RSAM with a finesse F = 20 can be estimated to● I sat,eff = 250 kW/cm 2● Φ sat,eff = 2.5 µJ/cm 2In this way the effective saturation values can be decreased to very low values at the expense of a small usuablespectral bandwidth.> Intensity dependent reflectanceSeongKyeong Photonics 20 info@skphotonics.com
RSAM at λ = 1064 nm with front mirror reflection r f = 0.97,unsaturated absorption of A = 1.5% and resonance order m = 4> Relaxation timeThe saturable absorber layer consists of asemiconductor material with a direct bandgap, which is slightly smaller than thephoton energy. During the absorptionelectron-hole pairs are created in the film.The relaxation time τ of the carriers is veryshort due to fast non-radiative relaxationchannels introduced by low-temperaturegrowth of the absorber layer.Recovery of the absorption A 0with a relaxation time τ = 10 psTypical values of the relaxation time τ arebetween 5 and 20 ps.The relaxation of the carriers and therecovery of the absorption A(t) after thesaturation can be described asA(t) = A 0 [1 - exp(-t/τ )]withA(t)A 0tτtime dependent absorptionsmall signal saturable absorptiontimerelaxation timeSeongKyeong Photonics 21 info@skphotonics.com
Page 1: SAM ® - saturable absorber mirrorp
Page 8 and 9: A SAM consists of a Bragg-mirror on
Page 10 and 11: eq.(2)withAA 0absorptionsmall signa
Page 12 and 13: The reflection bandwidth of the SAM
Page 14 and 15: The transmittance of the saturable
Page 16 and 17: Refractive index > GaAs | AlAs | Al
Page 18 and 19: Resonance wavelength for perpendicu
Page 24 and 25: The effective saturation fluence Φ

SAM – saturable absorber mirror

Create successful ePaper yourself

Delete template?

Save as template?