# Non-linear crystal choice

I am trying to find a non-linear crystal for sum-frequency generation combining 990nm from Ti:S laser with weak signal i.e. 812nm emitting from single photon emitters (these are details not the most important: polaritons strongly interacting (photon blockade) to 446nm using birefrigent phase matching. However, I have not found any previous papers which allowed me to compare with. Considering the maximum efficiency, is LBO a good choice? Or KTA, BBO? We have a pico-second Ti:S laser, with diffraction limited beam, and the walk off could be a problem, Pulse width 4 ps, Pulse duration 13ns, around 100W peak power.

• Do you have two Ti:Sa lasers emitting at the two given frequencies? How do you control the jitter between the two? – user_na Mar 13 '17 at 23:14
• I have improved my question. – el psy Congroo Mar 14 '17 at 8:19
• Please show your attempt to calculate the relevant parameters. – sammy gerbil Mar 14 '17 at 20:57

I would go for BBO. It typically has the highest non-linear coefficient and very good phase matching properties. According to SNLO you can use BBO in the following configurations:

990.0(o)+  812.0(o)=  446.1(e)
Walkoff [mrad]   =     0.00   0.00  62.67
Phase velocities = c/  1.656  1.660  1.658
Group velocities = c/  1.676  1.684  1.723
GrpDelDisp(fs^2/mm) =   51.7   73.4  165.6
At theta             =   26.2    deg.
deff                 =  2.01E0   pm/V
S_o × L^2            =  3.04E7   Watt
Crystal ang. tol.    =    0.43   mrad°cm
Temperature range    =   26.51   K°cm
Mix accpt ang =     0.95    0.78 mrad°cm
Mix accpt bw  =    21.23   25.48 cm-1°cm

990.0(e)+  812.0(o)=  446.1(e)
Walkoff [mrad]   =    70.15   0.00  73.36
Phase velocities = c/  1.613  1.660  1.639
Group velocities = c/  1.632  1.684  1.700
GrpDelDisp(fs^2/mm) =   42.9   73.4  156.3
At theta             =   36.0    deg.
deff                 =  1.33E0   pm/V
S_o × L^2            =  6.73E7   Watt
Crystal ang. tol.    =    0.64   mrad°cm
Temperature range    =   28.12   K°cm
Mix accpt ang =    19.13    0.67 mrad°cm
Mix accpt bw  =    14.72   60.09 cm-1°cm

990.0(o)+  812.0(e)=  446.1(e)
Walkoff [mrad]   =     0.00  72.20  75.24
Phase velocities = c/  1.656  1.608  1.630
Group velocities = c/  1.676  1.630  1.690
GrpDelDisp(fs^2/mm) =   51.7   61.2  152.0
At theta             =   40.2    deg.
deff                 =  1.15E0   pm/V
S_o × L^2            =  8.79E7   Watt
Crystal ang. tol.    =    0.76   mrad°cm
Temperature range    =   28.76   K°cm
Mix accpt ang =     0.79   16.58 mrad°cm
Mix accpt bw  =    71.89   16.79 cm-1°cm

• In order for your answer to be more self-contained, please tell us what SNLO is. Thanks. – garyp Mar 14 '17 at 12:48
• @Jannick I have used SNLO, but could you tell me why a large walkoff angle wouldn't bother you considering as a good candidate? Does it mean the walk off angle is only a problem for the fundamental waves? not for the second order wave? 73.36 radian is so large. – el psy Congroo Mar 15 '17 at 7:58
• I compared it to the other typical nonlinear crystals and their walkoffs were somewhat smaller but in a similar range. On the other hand the nonlinear coefficient of bbo is much larger so that you can use a shorter crystal, which makes walkoff less of an issue. – Jannick Mar 15 '17 at 11:15