The patent-pending HD 1800 line pairs per millimeter volume phase holographic transmission gratings are suitable for optical coherence tomography and other applications around 840 nm. Available from Wasatch Photonics Inc., they exhibit wider bandwidth than other gratings with similar dispersion. Offering peak diffraction efficiencies above 80 percent, they conserve much of the light for broadband applications. The company says that the devices solve the problems of narrow bandwidth and polarization-dependent losses. They are exposed using well-collimated laser light in dichromated gelatin. After processing, they are capped with protective glass covers and receive antireflection coating. They exhibit low scatter, high diffraction efficiency, high dispersion and wavefront distortion of <λ/2 rms at 632.8 nm over 1 in.