I see issues with how this firmware is currently set. Is this the firmware provided with this laser or have you updated it?
Here is the official documentation for Grbl 1.1. This is a good resource and should be understood when adjusting these settings.
When enabled, Grbl will move continuously through consecutive
G2 , or
G3 motion commands when programmed with a
S spindle speed (laser power). The spindle PWM pin will be updated instantaneously through each motion without stopping. Please read the GRBL laser documentation and your laser device documentation prior to using this mode. Lasers are very dangerous. They can instantly damage your vision permanently and cause fires. Grbl does not assume any responsibility for any issues the firmware may cause, as defined by its GPL license.
When disabled, Grbl will operate as it always has, stopping motion with every
S spindle speed command. This is the default operation of a milling machine to allow a pause to let the spindle change speeds.
Grbl needs to know how far each step will take the tool in reality. To calculate steps/mm for an axis of your machine you need to know:
The mm traveled per revolution of your stepper motor. This is dependent on your belt drive gears or lead screw pitch.
The full steps per revolution of your steppers (typically 200)
The microsteps per step of your controller (typically 1, 2, 4, 8, or 16). Tip: Using high microstep values (e.g., 16) can reduce your stepper motor torque, so use the lowest that gives you the desired axis resolution and comfortable running properties.
The steps/mm can then be calculated like this: steps_per_mm = (steps_per_revolution*microsteps)/mm_per_rev
Compute this value for every axis and write these settings to Grbl.
$100=250.000 X steps/mm
$101=250.000 Y steps/mm
$102=250.000 Z steps/mm