</span><span class="n">spec</span><span class="p">)</span>
  <span class="c">!! Returns the wavenumber spectrum array of the spectrum instance.</span>
  <span class="k">class</span><span class="p">(</span><span class="n">spectrum_type</span><span class="p">),</span><span class="k">intent</span><span class="p">(</span><span class="n">in</span><span class="p">)</span> <span class="kd">::</span> <span class="n">self</span> <span class="c">!! Spectrum instance</span>
  <span class="kt">real</span><span class="p