如何在Elastic Search-PHP [1.0]客户端中返回特定字段

I am using Elasticsearch-PHP [1.0] client (link below):

[1]: https://www.elastic.co/guide/en/elasticsearch/client/php-api/current/_quickstart.html

I want to return specific fields from elastic search..I have written the following code :

$params['body']['fields'] = ["title","prod_desc"];

but it's not working..Please Help..