How to filt data by time using Laravel?

I have this query, I would like to obtain only the data created on the current month

public function index(Request $request)
{

    if($request->ajax())
    {
        $data = DB::table('tbl_lista_contactabilidad as a')
    ->select('a.id','a.rif','a.razon_social','a.postventaatcs_id','fecha_contacto','a.contactado','a.persona_contacto','a.correo_contacto','a.celular_contacto','a.numero_contacto','a.comentarios','a.auditado')
    ->leftjoin('tbl_equipo_postventaatcs as h','h.id','=','a.postventaatc_id')
    ->leftjoin('users as l','l.id','=','h.asesor_id')
    ->leftjoin('tbl_lista_respuestas as b','b.id','=','a.auditado')
    ->leftjoin('tbl_lista_respuestasc as c','c.id','=','a.contactado')
    ->where('l.idop', auth()->user()->idop)
    ->where('a.estatus','=',1)
    ->select(array('a.id','l.name as idop_asesor','l.apellido as ape_asesor','l.idop','a.rif','a.razon_social','a.estatus','fecha_contacto','a.contactado', 'a.persona_contacto','a.correo_contacto','a.celular_contacto','a.numero_contacto','a.comentarios','a.auditado','b.respuesta','c.respuestac'));

    }

    return view('contactabilidadasesor');
}

via Chebli Mohamed