Event after an AlertController is open?

Hi all ! Could anyone suggest please … how to catch event after alertCtrl.present() ? I want to set focus to input with id Search after alertCtrl.present …

    let alertCtrl = this.alertCtrl.create({
      title: 'Filter by Serial Number',
      inputs: [{
        name: 'sn',
        id: 'Search',
      }],
      buttons: [
        {
          text: 'Filter',
          handler: (data) => {
          }
        },
        {
          text: 'Cancel',
          handler: () => {
            event.preventDefault();
          }
        }
      ]
    });
    alertCtrl.present().then(() => {


    });