slm Subroutine

        subroutine slm(this, spectrum, dict, seqs)
            !! image source
            ! TODO fix hardcoded size of 200
            ! investigate +2 error
            use piecewiseMod
            use tomlf,         only : toml_table, get_value
            use random,        only : ran2, seq
            use sim_state_mod, only : state
            use constants,     only : TWOPI

            class(photon) :: this
            !> Input image to sample position from
            type(spectrum_t),           intent(in)    :: spectrum
            !> Metadata dictionary
            type(toml_table), optional, intent(inout) :: dict
            !> random numbers from a sequence. Quasi-Monte Carlo
            type(seq),        optional, intent(inout) :: seqs(2)
            
            integer :: cell(3)
            real(kind=wp) :: x, y

            this%pos = photon_origin%pos
            call spectrum%p%sample(x, y)
            this%pos%x = (x-100) / (state%grid%nxg / (2.*state%grid%xmax))
            this%pos%y = (y-100) / (state%grid%nyg / (2.*state%grid%ymax))

            this%nxp = photon_origin%nxp
            this%nyp = photon_origin%nyp
            this%nzp = photon_origin%nzp

            this%phi  = atan2(this%nyp, this%nxp)
            this%cosp = cos(this%phi)
            this%sinp = sin(this%phi)
            this%cost = this%nzp
            this%sint = sqrt(1._wp - this%cost**2)  

            this%tflag  = .false.
            this%cnts   = 0
            this%bounces = 0
            this%layer  = 1
            this%weight = 1.0_wp

            this%phase = 0.0_wp
            this%wavelength = 500.e-9_wp
            this%energy = 1._wp
            this%fact = TWOPI/(this%wavelength)

            ! Linear Grid 
            cell = state%grid%get_voxel(this%pos)
            this%xcell = cell(1)
            this%ycell = cell(2)
            this%zcell = cell(3)

        end subroutine slm