Infra-Red Optical Sources
Development of Optical Parametrical Oscillators Tunable in the Mid - IR Region (4.5 – 12 mkm) with a Narrow Spectral Bandwidth of Output Radiation and Increased Conversion Efficiency
Tech Area / Field
- PHY-OPL/Optics and Lasers/Physics
3 Approved without Funding
NPO Astrophysica, Russia, Moscow
- Institute of Spectroscopy, Russia, Moscow reg., Troitsk\nKuban State University, Russia, Krasnodar reg., Krasnodar
Project summaryThe purpose of the present project is development and manufacturing of the pilot samples of a new generation of nanosecond and picosecond optical parametrical oscillators based on the new nonlinear crystals, tunable over the mid - IR range with high power/energy level and a narrow spectral bandwidth of output radiation. Usually in the literature nanosecond oscillators are called OPO, and picosecond ones are called OPG. For simplicity, we shall name them throughout the present text as OPO.
Nowadays optical parametrical oscillators both of nanosecond and picosecond pulse duration are among the most effective sources of tunable radiation in the mid - IR region. The OPO pumped by the most technological and widespread Nd - lasers (λ = 1.06 μm) are of the special interest. The range of application of such oscillators is very wide: monitoring of atmospheric pollution, manufacture of superpure materials and materials with specified properties, sensitive detectors for medicine and biology, scientific researches. For successful use OPO should have a wide tuning range ( Δλ~ 1 micron in a spectral region of 4.5 - 12 microns, a sufficient level of average power (~ 0.1 W) or energy in a pulse (~ 10 mJ), high conversion efficiency (~10 %) and a narrow radiation bandwidth (Δν ~ 0.1 cm-1, nanosecond OPO).
The Research & Development work suggested in the present project is a logic continuation of ISTC project #2334. As a result of its accomplishment the experimental samples of nanosecond and picosecond pulse duration OPO with wavelength tuning over the mid - IR range (3 – 10 m) and average power up to 0.1 W, energy differential conversion efficiency 5 - 7 % and linewidth ~ 10 cm -1 have been manufactured. The optical parametrical oscillators made on the basis of above prototypes may be widely used in various applications. However, for the solving of many practical tasks (gas-analysis tasks, making of devices for monitoring of environment, lidars, etc) OPOs with high conversion efficiency, high output power and a narrow spectral bandwidth are required. Thus, a making of such OPOs needs simultaneous solving of the following problems:
- increasing of conversion efficiency and output energy of pulses (up to 10 mJ) or average power (0.1 - 1 W);
- narrowing of generated spectrum, for picosecond OPG - up to 4-6 cm-1 with ultimate aim to reach near Fourier-transform limited bandwidth, for nanosecond OPO up to value ~ 0.1 cm -1.
The main problem arising when developing mid - IR OPO with pumping by one-micron radiation is a rather low quantum conversion efficiency (here it is determined as λp/λ, where λp – wavelength of pumping) and as result - rather low output energy / power of radiation. So, for example at pumping wavelength close to 1.06 μm and wavelength of OPO - 8 μm the quantum conversion efficiency will be 13%, i.e. the possible maximum conversion efficiency cannot exceed this value. The real value of it is usually even lower. There are two possible ways to increase the conversion efficiency and the output energy / power:
- to set into a cavity of OPO additional sources of signal and/or idler waves by injection of a seed radiation (SR) or by intracavity conversion of radiation frequency;
- to use pumping radiation more effectively because the larger part of a pumping pulse energy usually is not converted - partially due to remarkable delay between the OPO pulse in steady state mode and the pumping one.
The possible solution of the problem may be achieved by the use of the special schemes of pumping, and by the introducing of some nonlinear interaction into OPO. Recently, the team of researches from FSUE «SPA Astrophysica», IS RAS and collaborators under ISTC project # 2334 suggested and developed a number of new various schemes, both of OPO itself and the ways of their pumping and SR injection. These schemes make it possible to increase both output pulse energy / power and conversion efficiency of the OPO. This conclusion is based on our estimations and theoretical analysis of the similar schemes.
It is important to note, that proposed concrete schemes (see below) are not verified experimentally and are not studied theoretically in details. Therefore, during the work under the present project it is supposed to carry out the studies of the suggested schemes in detail. The results of these studies have also an independent scientific interest and will allow to understand more in the physics of complex nonlinear optical processes.
The tuning of OPO wavelength will be produced by use of traditional ways such as turning of a crystal in a phase matching plane and/or by temperature tuning. For narrowing of generation spectrum we propose to develop and insert into OPO/OPG scheme a spectral narrowing system based on dispersive elements, filters or SR injection and to insert a spatial filtration of pump radiation to increase pulse-to-pulse stability of a spectrum.
Moreover, for the solving of the problems mentioned above it is planned to use new crystals such as HgGa2S4, Hg1-xCdxGa2S4, AgGaS2 which possess a high nonlinearity and are of the best optical quality. These crystals were developed within the framework of the ISTC Project #1897 by the authors of the proposed work and by our colleagues from Kuban State University, who are supposed to take part in the present project as the experts and for preparation of necessary crystals.
As a result of the present project the following prototypes of the OPO will be developed and manufactured:
- nanosecond OPO pumped by YAG:Nd laser with wavelength tuning over the mid - IR range (4.5 - 12 μm), with pulse energy 1 - 10 mJ, average power 0.1 - 1 W, energy conversion efficiency more than 10 % and spectral linewidth ~ 0.1 cm- 1;
- picosecond OPG pumped by YAG:Nd laser with wavelength tuning over the mid - IR range, with high quantum efficiency – up to 8-12 % (λ ~ 5 μm) and spectral bandwidth ≤4-6 cm-1.
The results of studies carried out along the project and the obtained data will be used for development of the new generation of OPOs and for improvement of existing models of commercially available devices.