def Q(wavelength):
    """Returns the technologically achievable focusing (Q-factor)
    (Earth 2007 tech) for a given wavelength (in m)"""
    wavelength = wavelength / 10**-9
    if wavelength > 300:
        Q = 1.22
    else:  # power-law fit to values from Earth 2017 technology (see Figure)
        Q = 1 / ((5.21575598 * (wavelength / 1000)**1.20669934) / 1.22) + 0.22
    return Q