Extra dimensions and Higgs pair production at photon colliders

We show that new physics effects due to extra dimensions can dramatically affect Higgs pair production at photon colliders. We find that the cross section due to extra dimensions with the scale $M_S$ of new physics around 1.5 TeV can be as large as 0.11 pb (1.5 pb) for monochromatic photon collision, $\gamma \overrightarrow{\gamma }HH,$ with the collider energy $\sqrt{s}=0.5\mathrm{}\left(1\right)\mathrm{}$ TeV for a Higgs boson mass of 100 (350) GeV. The cross section can be 3 fb (2.7 fb) for the same parameters for collisions using photon beams from electron or positron back scattered by laser. These cross sections are much larger than those predicted in the standard model. Higgs pair production at photon colliders can provide useful tests for new physics due to extra dimensions.