google drive api to fetch specific subfolder inside the root one

Question

Since I'm working with the Google Drive API, I was able to use the code below to fetch the data from the Google Drive inside a folder. However, I'm wondering if there's a way to specify the subfolder. In some scenarios, I may have two folders, with same name subfolders and in those cases, the data is returned from the very first folder that it finds. Therefore, I would like to specify using "/ "for example data/onefor now if I pass data in post that gives me response.

            $this->folder_name = trim($_POST['folder_name']);   
            $service = new Google_Service_Drive($this->gdrive->client);
                        $this->search_result = $service->files->listFiles(array(

                'q' => "name='".$this->folder_name."'",                  

                ));

I wish to use the Google API to obtain the data from the specified subfolder.