Problems with my 2d Topdown game.

So I made so that the player looks at my mouse, but I gave him a little delay by rounding up the rotation value or sth. (What I wanted to say is that I have no idea about how I did it) Then I made a laser for aiming using raycast and a line renderer. Everything works fine .... buuuuuut, if I set my smoothing to something other than 0 ... means no smoothing, the laser starts lagging and jumping forth and back if I move (And ONLY if I move). Line Renderer is not the problem, raycast isnt aswell. So I think that my smoothing is crap ... If anyone wants to help, heres the code. Laser object is a child of the player btw.

Player

  using UnityEngine;
  using System.Collections;

  public class Player : MonoBehaviour {

 //Variables
 public float movSpeed = 90;
 Rigidbody2D rb2d;

 private float zVelocity = 0.0F;
 
 public float smooth;
 //Code

 void Start() {
     //Define stuff
     rb2d = gameObject.GetComponent<Rigidbody2D>();
 }

 void FixedUpdate(){
     //Movement
     Vector2 input = new Vector2 (Input.GetAxisRaw ("Horizontal"), Input.GetAxisRaw ("Vertical"));
     rb2d.AddForce(input * movSpeed);
     if (Mathf.Abs(rb2d.velocity.x) > movSpeed){
         rb2d.velocity = new Vector2(Mathf.Sign(rb2d.velocity.x)* movSpeed, rb2d.velocity.y);
     }
     if (Mathf.Abs(rb2d.velocity.x) > movSpeed){
         rb2d.velocity = new Vector2(rb2d.velocity.x, Mathf.Sign(rb2d.velocity.y) * movSpeed);
     }
 }
 void Update() {
     //Follow mouse
     Vector3 diff = Camera.main.ScreenToWorldPoint(Input.mousePosition) - transform.position;
     diff.Normalize();
     float rot_z = Mathf.Atan2(diff.y, diff.x) * Mathf.Rad2Deg;
     float z = Mathf.SmoothDampAngle(transform.eulerAngles.z,rot_z - 90, ref zVelocity, smooth);
     transform.rotation = Quaternion.Euler(0f, 0f, z);
 
     }
 }

Laser

 using UnityEngine;
 using System.Collections;

 public class Laser : MonoBehaviour {
 
 LineRenderer lineRenderer;
 public Vector2 laserHit;
 public LayerMask layerMask;
 Vector3 pointInfront;
 Vector4 laserGray;
 public Material laserMat;
      
 void Start () {
    lineRenderer = gameObject.AddComponent<LineRenderer>();
     laserGray = new Vector4(0,0,0,0.2f);
 }

 void Update(){
     pointInfront = transform.up * 30 ;
 }

 void LateUpdate () {

     //Raycasting
     RaycastHit2D hit = Physics2D.Raycast(transform.position, transform.up, 30, layerMask);
     Debug.DrawRay(transform.position, transform.up*100);
     if (hit.collider != null){
         laserHit = hit.point;
     lineRenderer.SetPosition(0, transform.position);
     lineRenderer.SetPosition(1, laserHit);
     lineRenderer.SetWidth(0.08f,0.05f);
     lineRenderer.material = laserMat;
     }
     else {
     lineRenderer.SetPosition(0, transform.position);
     lineRenderer.SetPosition(1, transform.position + pointInfront);
     lineRenderer.SetWidth(0.08f,0.05f);
     lineRenderer.SetColors(laserGray,laserGray);
     lineRenderer.material = laserMat;
     }
 }
 }