National Institute of Standards & Technology, Acquisition & Assistance Div., Bldg. 301, Rm B117, Gaithersburg, MD 20899

66 -- TUNABLE DIODE LASER SYSTEM SOL 53SBNB7C1119 DUE 053097 POC Julie Liu (301)975-6727, Fax (301)963-7732 WEB: NIST Contracts Homepage, http://www.nist.gov/admin/od/contract/contract.htm. E-MAIL: NIST Contracts Office, Contract@nist.gov. This announcement modifies the original announcement published April 14, 1997 and the modification published May 5, 1997. The date and time for receipt of quotations is extended to 3 PM EST on May 30, 1997. The specification stating, "at least one scheme shall be capable of measuring a minimum CO absorbance of 10E-5 with a signal-to-noise ratio of unity, with an averaging time of no more than 1 second." is replaced by, "at least one scheme shall be capable of measuring a minimum CO absorbance of 0.00001 with a signal-to-noise ratio of unity, with an averaging time of no more than 1 second." The following questions have been received from potential offerors: 1) Q. A GRIN lens is specified for the fiber collimator output of the single mode fiber. If an anti-reflection coated aspheric lens provides equivalent operation, can this be substituted? A. An anti-reflection-coated aspheric lens may be substituted in place of the GRIN lens at the output of the single mode fiber if it provides equivalent operation.2) Q. The output laser power from the optically-isolated fiber is specified as at least 5mW. Is it possible to substitute an otherwise suitable laser source providing at least 2 mW of power from the fiber output? A. The output laser power from the optically-isolated fiber is specified as at least 5 mW for the purpose of providing adequate power to survive attenuation by soot. For the laser wavelength of 1.55 microns along a 2 cm path, typical soot volume fractions in the vicinity of a fire could attenuate as much as 90% of the incident beam intensity. In light of this, substitution of a laser with 2 mW usable power for the specified 5 mW laser is acceptable only if the system is capable of measuring the required CO absorbance of 0.00001 with low signal levels resulting from soot attenuation. 3) Q. Detection scheme [1] is described as an electronic balancing method and must be capable of absorbance sensitivity of 10 -5. The reference type for this circuit described in reference 1 is not electronically balanced and has only been shown to allow absorbance sensitivity of 10 -3. Is an electronically balanced direct absorption detector such as described by P.C.D. Hobbs, "Ultrasensitive laser measurements without tears, " Applied Optics, Vol. 36, No. 4, pp. 903-920, 1997 acceptable? A. Yes, this is acceptable for detection scheme [1]. 4) Q. Will the Government accept alternative approaches to the specified system? A. Offerors are encouraged to submit alternate approaches. First, submit a quotation on the system as specified, then submit a separate quote for the alternate. (0143)

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