One way to write bragg holographic grating is to use the phase mask. if the period of phase mask is 1 micron and the refractive index of recording materail n =1.5
(a) find the period of trecorded bragg grating
(b) what is the resonant wavelength of this bragg grating.
(c) if the number of grating period is 1000, and the refreactive index modulation is △n= 0.0001， estimate the spectral width of reflection spectrum at the resonant wavelength.

What is the momentum of a 2 kg object moving at 15 meters per second

Very large accelerations can injure the body, especially if they last for a considerable length of time. one model used to gauge the likelihood of injury is the severity index ( ), defined as =/ . in the expression, is the duration of the accleration, but is not equal to the acceleration. rather, is a dimensionless constant that = the number of multiples of that the acceleration is equal to.in one set of studies of rear-end collisions, a person's velocity increases by 13.7 km/h with an acceleration of 36.0 m/s2 . let the + direction point in the direction the car is traveling. what is the severity index for the collision?

Alead ball is dropped into a lake from a diving board 5m above the water . it hits the water with a certain velocity and then sink with constant velocity in bottom . it reaches the bottom 5 second after it is dropped if g= 10m/s2 . find depth of the lake and average velocity of the ball ?