We study the fourth-order squeezing in the most general case of superposition of two coherent states by considering <\psi \right |(\Delta X\theta )4\left | \psi > where X\theta = X1\mathop {\mathgroup \symoperators cos}\nolimits \theta + X2\mathop {\mathgroup \symoperators sin}\nolimits \theta ,\mskip \thickmuskip X1 + iX2 = a is annihilation operator, \theta is real, \left | \psi \right \rangle = Z1 \left | \alpha \right \rangle + Z2 \left | \beta \right \rangle , \left | \alpha \right \rangle and \left |\beta \right \rangle are coherent states and Z1, Z2, \alpha , \beta are complex numbers. We find the absolute minimum value 0.050693 for an infinite combinations with \alpha - \beta =1.30848 exp [\pm i(\pi /2) + i\theta ], Z1/Z2 = \mathop {\mathgroup \symoperators exp}\nolimits (\alpha \ast \beta - \alpha \beta \ast ) with arbitrary values of \alpha + \beta and \theta . For this minimum value of < \psi \right |(\Delta X\theta )4\left | \psi > , the expectation value of photon number can vary from the minimum value 0.36084 (for \alpha +\beta = 0) to infinity. We note that the variation of < \psi \right |(\Delta X\theta )4\left | \psi > near the absolute minimum is less flat when the expectation value of photon number is larger. Thus the fourth-order squeezing can be observed at large intensities also, but settings of the parameters become more demanding.
PACS numbers: 42.50.Dv
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