webcam Capture from webcam encountered: IndexOutOfRangeException: Array index is out of range

I 'm trying to call the webcam from the plane object, and planning to capture the image from there. But my class library encountered an error

"IndexOutOfRangeException: Array index is out of range."

Just a simple code, yet I failed to figure out why.

 public class CameraCapture : MonoBehaviour {
     private WebCamTexture webcamTexture;
     private Texture2D textureImg;
     private int imgWidth = 640;
     private int imgHeight = 480;
     private GameObject plane;
     private Texture2D videoTexture;
     private Texture2D tmp;
 
 void Start () {
         WebCamDevice[] devices = WebCamTexture.devices;
         Debug.Log("devices"+ devices.Length);
 
         videoTexture = new Texture2D(imgWidth, imgHeight, TextureFormat.RGB24, false);
         tmp = new Texture2D(imgWidth, imgHeight, TextureFormat.RGB24, false);
 
         textureImg = new Texture2D(imgWidth, imgHeight, TextureFormat.RGB24, false);
         webcamTexture = new WebCamTexture(devices[1].name, imgWidth, imgHeight, 60);
         webcamTexture.Play();
 
         plane = GameObject.Find("Plane");
 } }

Any advice ? thanks in advance.