Lidar has been proven to be a powerful tool for the atmospheric detection due to the advantage of high spatial and temporal resolution. And multi-wavelength lidar can obtain more atmospheric optical properties, which can be inverted to the particle microphysical properties. However, in the multi-wavelength lidar, classical transmission beam expanders of simple structure are difficult to achieve simultaneous beam expansion at multiple wavelengths because of the impact brought by chromatic aberration. To solve this problem, we design an off-axis reflective beam expander with only two spherical mirrors and applied it in the multi-wavelength Raman lidar system. The main parameters of the beam expander have been analyzed in detail and optimized by the Zemax software. And we also design a simple mechanical structure for adjustment of the beam expander which was demonstrated experimentally. According to the receiver field-of-view (FOV), the divergence angle of the emitted laser is less than 0.4 mrad. The experimental results show that the beam expander can be applied well in the multi-wavelength Raman lidar system. Keywords: Off-axis beam expander, Multi-wavelength Raman
High-spectral-resolution lidar (HSRL) has the advantages of high spatial and temporal resolution, high detection accuracy as well as strong signal-to-noise ratio. However, the stability of emitted laser frequency is crucial for the accuracy of HSRL inversion data. To ensure the data quality of HSRL, we have constructed a compact, low-cost but satisfactory frequency locking system based on an iodine absorption cell and STM32 Microprogrammed Control Unit (MCU). MCU acquires the spectrum transmittance of the iodine cell, and employs the proportional integral differential (PID) algorithm to control the drive current of seed laser; thereby the frequency of the emitted laser is locked to one of the iodine absorption line. According to the experimental results, a considerable frequency standard deviation of 4 MHz is achieved. Furthermore, the performance of this system during HSRL long-term observations is also proved to be stable and reliable
The spectroscopic filter plays a critical role in an HSRL (high-spectral-resolution lidar) system. In this paper, a pressuretuned field-widened Michelson interferometer (PT FWMI for short) is proposed. The design of the pressure tuning and the field widening of the PT FWMI are addressed in detail, and the development of a laboratory demonstrator is described as well. The optical elements contain a solid arm made of the glass H-ZF52 with the dimension of 59.572 mm, and an air gap with the length of 32.889 mm within the sealed chamber of 1 atm. Due to the matched dimensions and refractive indices of the two arms, the experimental testing results show that the OPD variation of the developed PT FWMI is about 0.13 lambda and the RMS is less than 0.03 lambda when the divergent angle is as much as 3 degree (half angle). The filtering performance of the prototype developed is scanned with a frequency tunable laser whose bandwidth is 10MHz. Results revealed that bright to dark fringe contrast of the spectroscopic filter is approximately 33. In conclusion, this newly proposed pressure tuning design is suitable for developing stable and tunable FWMI spectroscopic filters and paves the way for designing a robust near infrared HSRL system.
Access to the requested content is limited to institutions that have purchased or subscribe to SPIE eBooks.
You are receiving this notice because your organization may not have SPIE eBooks access.*
*Shibboleth/Open Athens users─please
sign in
to access your institution's subscriptions.
To obtain this item, you may purchase the complete book in print or electronic format on
SPIE.org.
INSTITUTIONAL Select your institution to access the SPIE Digital Library.
PERSONAL Sign in with your SPIE account to access your personal subscriptions or to use specific features such as save to my library, sign up for alerts, save searches, etc.