Set the relaxation dispersion spin-lock field strength (nu1).
spectrum_id: The spectrum ID string to associate the spin-lock field strength to.
field: The spin-lock field strength, nu1, in Hz.
This sets the spin-lock field strength, nu1, for the specified R1rho spectrum in Hertz.
To set a spin-lock field strength of 2.1 kHz for the spectrum `nu1_2.1kHz_relaxT_0.010', type one of:
[numbers=none] relax> relax_disp.spin_lock_field(2100, 'nu1_2.1kHz_relaxT_0.010')
[numbers=none] relax> relax_disp.spin_lock_field(field=2100, spectrum_id='nu1_2.1kHz_relaxT_0.010')