Meadowlark Optics (United States)

Liquid crystal on silicon (LCoS) spatial light modulators (SLMs) are versatile scientific tools relevant to an increasingly wide variety of research and technological applications including digital holography, wavefront correction, optical tweezing, and non-mechanical beam steering to name a few. Since SLMs are used in a multitude of different ways, some aspects of device performance (e.g., response time) are crucial to certain applications while being irrelevant to others. In this work we couple our standard SLMs with a thermo-electric cooler, allowing for tunability of the device operating temperature from 0° to 75 °C. We show that there is an inherent tradeoff between the liquid crystal response time and the phase stability of an SLM, and that the operating temperature offers a means of controlling this tradeoff. Furthermore, this paper aims to provide the reader with a brief but thorough explanation of SLM operating principles and device structure, defines the performance metrics of the SLM, and provides a methodology for measuring the specifications. By allowing control over the SLM operating temperature and detailing how temperature affects device functionality, SLM users are afforded greater experimental flexibility and will be better able to tailor the performance of their device for the given project or application at hand.

Measured extinction ratio on high quality linear polarizers depends on test system geometry. The measurement becomes especially challenging for polarizers with extinction ratio expected to exceed 106. We describe methods capable of measurements of high purity polarizers at and above 106 extinction ratio. We discuss the geometrical factors affecting the measured results that may be pertinent in determining what performance is achievable in a users system. We describe methods for computing extinction ratios without an absolute reference perfect polarizer with infinite extinction ratio and for rank ordering performance of a set of several polarizers. Measurement results are presented for several high performance polarizers including Glan-Thompson polarizers, dichroic glass polarizers and Meadowlark Optics Ultra Broadband Polarizers.

The ability to accurately rotate the polarization of incident light while minimizing any losses in polarization purity has applications in optical switching, polarimetry, and microscopy. Polarization rotators utilizing tunable birefringent plates, such as liquid crystal (LC) devices, have the advantage of non-mechanically tuning the devices' retardance. However, these devices properly work with incident light within a very specific wavelength range. Ferroelectric liquid crystal (FLC) devices can switch between two orthogonal states of linear polarization, and offer response times much faster than their nematic liquid crystal cell counterparts. An achromatic polarization rotator can be constructed with an FLC cell between two half-wave plates that have been constructed to produce a half-wave retardance at a certain design wavelength. This results in a device that offers fast response times and high polarization purity over a broader wavelength range.

Liquid Crystal on Silicon (LCoS) Spatial Light Modulators (SLMs) are used as programmable adaptive optical elements1,2,3 in many applications involving high power lasers. In some cases, LCoS SLMs may be exposed to laser radiation that can cause permanent, irreparable damage to the SLM. The damage arises from a number of parameters including laser wavelength, pulse duration, pulse repetition rate, beam diameter, spatial profile, temporal profile, and even angle of incidence. This paper is an introduction and practical guide to understanding laser damage mechanisms and expected damage threshold levels for LCoS SLMs.

Abstract There is a variety of new polarization optics that can be employed for polarimetry and for polarization control. Many are enabled by new materials including polymers and liquid crystals. We survey here these and other relatively new devices and components available commercially that open new possibilities for astronomers.

Meadowlark Optics has successfully built and demonstrated a liquid crystal based tunable filter with novel FWHM tunability. This allows separate control over both the location of a narrow spectral bandpass and the width of the bandpass function. This non-mechanical, imaging filter thus enables random access of the visible to near IR spectrum and also controlling the specificity of the transmitted light. We will discuss both the relative trade-offs in this filter design space and present data from functional units.

The quest for higher performance optical parametric oscillators (OPOs) has been dominated largely by the pump laser requirements. Pump lasers with moderate average power, high peak power, good beam quality and low cost have not been readily available. Therefore, little data has been accumulated on the effects of average power operation in an OPO. A pump laser was constructed that has a high pulse repetition frequency (PRF), 1 Hz to 20 KHz, a modelocked/Q-switched temporal format, and an average power of greater than 40 Watts. Using this source, several types of synchronously pumped OPOs were tested for average power output and thermal effects. The highest performance to date was achieved with a LiNbO3 SRO in a ring resonator. LiNbO3 was the crystal chosen for its reasonable deff, thermal properties, and ease of obtaining large, good quality crystals.

While the liquid crystal industry is primarily driven by the display industry, increasingly important applications in science and engineering have emerged such as beam steering, wavefront modulation and polarization switching and control. We will discuss some of the differences in construction techniques needed to produce a precision optical device rather than a flat panel display along with development work being carried out at Meadowlark Optics in some of the above areas. These include polarization switches capable of greater than 5000:1 contrast and high efficiency beam steering for precision interferometer gauges.

LIQUID CRYSTALS SPATIAL LIGHT MODULATORS FOR PRECISION OPTICSAPPLICATIONSTom BaurMeadowlark Optics, Inc.7460 Weld County Road 1Longmont, CO 80504-9470(303)776-4068, (303)776-5856 (FAX)Meadowlark Optics has developed a variety of spatial light modulators (SLMs) fornondisplay applications. They operate by electrical control of the birefringence of nematicliquid crystals to achieve spatial and temporal modulation of phase and amplitude of light.They modulate phase by electrically varying the effective extraordinary index, n, of auniaxial layer of nematic liquid crystal. This varies the optical thickness of the layer for lightthat is linearly polarized parallel to the optic axis of the layer. The SLM's can modulateamplitude for light that is linearly polarized at 45° to this direction if they are followed by anorthogonal or parallel linear polarizer.The electrical control of the effective n and thus the control of birefringence meansthat each means spatial element or pixel of the SLM functions as a variable retarder. Thefigure below shows the relationship between applied voltage and retardance of a typical liquidcrystal variable retarder. Notice that the relationship is nonlinear and that a fixed subtractiveretarder must be added to reach zero retardance. The maximum retardance depends on thethickness of the liquid crystal layer. Typical thicknesses range from 1 .5 microns to 30microns. Most nematic liquid crystals have a birefringence (n-n0) in therange of 0.05 to0.25. Therefore, the available range of electrical control of retardance and of opticalthickness can be from as little as 75 nm for a thin layer of low birefringence liquid crystal toas much as 7.5 microns for a thick layer of high birefringence liquid crystal.E=