Generation of Coherent Radiation Continuously Tunable in 515-650-nm Range by Efficient Second Harmonic Conversion of LiF:F2- Laser Radiation
Alex Yu. Dergachev
Q-Peak, Inc.,
135 South Road, Bedford, Massachusetts 01730
Tel.: (781) 275-9535, FAX: (781) 275-9726, E-mail: dergachev@qpeak.com
Sergey B. Mirov
Physics Department, University of Alabama at Birmingham,
1300 University Blvd., Birmingham, Alabama 35294
Tel.: (205) 934-5318, FAX: (205) 934-8042, E-mail: mirov@phy.uab.edu
ABSTRACT
For the first time, to the best of our knowledge, we report on the application of non-critically phase-matched LBO crystals for generation of high power/ high energy coherent radiation in 515-650-nm range by efficient (~ 50%) frequency doubling of radiation from a LiF:F2- laser with 1030-1300-nm tuning range.
SUMMARY
Here we describe the use of a non-critically phase-matched, temperature-tuned LBO crystal as an efficient material for second harmonic generation (SHG) of fundamental wavelengths of the LiF:F2- laser, which has a 1030–1300-nm tuning range. The theoretical temperature-tuning curve for the LBO crystal, based on the data for refractive indexes and their dependence on the temperature given by Kato 1, is shown in Fig.1. As one can see, by changing the temperature of the LBO crystal, it is possible to maintain non-critical phase-matching conditions for the whole tuning range of LiF:F2- laser (see Fig.1).
Fig. 1. 1) Calculated temperature-tuning curve for second harmonic generation in non-critically phase-matched LBO crystal (Type I), 2) Tuning curve of room-temperature LiF:F2- laser.
LiF:F2- is an efficient, room-temperature, stable color center laser, which can be pumped by the radiation of any laser or laser diode emitting in the 900-1070-nm range. The fundamental tuning range for a LiF:F2- laser is 1030-1300 nm when pumped near the absorption peak of F2- color centers in the 900-960-nm range.
The fact that the LBO material is maintained under non-critical phase-matching conditions allows for the following advantages: zero walk-off, wide spectral acceptance bandwidth, wide angular acceptance bandwidth and therefore the possibility for tight focusing of the fundamental beam. Moreover, the extremely high optical damage threshold of LBO material makes it very attractive for nonlinear conversion of high-energy lasers.
Proof-of-principle experiments were performed in the following configuration. The room temperature LiF:F2- laser was pumped by the radiation of Ti:Sapphire laser at 946 nm (Epulse = 100 mJ, tpulse =40 ns, fpulse = 10 Hz) and tuned to approximately 1190 nm which corresponds to the non-critical phase matching in LBO crystal at room temperature. Maximum energy per pulse achieved at 1190 nm was 40 mJ.
Radiation of the LiF:F2- laser was focused into 15-mm-long LBO crystal. The second harmonic beam was separated from the fundamental beam using Pellin-Broca prism. Total energy per pulse incident on the LBO crystal was 35 mJ. Total energy per pulse exiting the crystal at both wavelengths (fundamental and SHG) was 32 mJ. Total energy per pulse at 595 nm (SHG) was 15 mJ. Therefore, the conversion efficiency for SHG approached ~50%.
We demonstrated, to the best of our knowledge, the highest conversion efficiency for the frequency doubling of the LiF:F2- laser. The LiF:F2- - LBO combination can be used as an efficient all-solid-state source of coherent radiation in 515-650 nm range.
References:
1. K. Kato, IEEE J. of Quant. El. Vol. 30, p. 2950 (1994)
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