How to set Axis step in Google Chart?

I'm wondering how to set axis step in a google chart built from JavaScript? I use this to set min and max:

vAxis: {
title: 'temps (ms)',
    viewWindowMode: 'explicit',
    viewWindow: {
        max: 180,
        min: 0
    },
}

And I need to add an other constraint to fix vertical step to 0.1 for example.