Modular Spectrometer

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How does a spectrometer work?

A light is delivered to the spectrometer by a fiber cable. The light passes through a slit and is reflected off a column in the mirror. A parallel beam of light is directed to a diffraction grating. Diffraction grating breaks the light up into a spectrum directed to a focus in the air. And the focusing of directs the spectrum to a detector. Detector is one exo high camera and measure the intensity of each color in the spectrum. And basically that's how a spectrometer works.

What is modular spectrometer?

Micro spectrometer just looks like modulars, so called modular spectrometer. Optosky ATP2000P is one of the most popular model sold many quantities all over the world. The ATP1010 has the most miniature size only larger than a coin. Then the longer spectrometer for being installed a fan inside, in the right part has left ventilation port. In most case, the cooled spectrometers need to install fan for heat ventilation.

What is called micro spectrometer or fiber optic spectrometer?

In most case we use fiber to introduce light to a spectrometer, so called optic fiber spectrometer, and also being named micro spectrometer for compact size, mirco spectrometer common size is about 10cm, no exceeding 20cm, maybe you can not imagine most common spectrometers even have a normal size of 40-50 cm.

What is a spectrometer used for?

There is an incandecent light can generate white light, going through to a spectrometer can disperse multi-colors, although seen in naked eyes it’s a white light, but being analyzed by the spectrometer can display rainbow colors, export to PC to readout spectrum, this white light shows different wavelengths and intensity information.

What is the function of a spectrometer?

It's used to measure light intensity of UV, VIS, NIR and IR.

what is the working principle of a spectrometer?

The Light goes through incident slit to form the paralleled light, this is grating can disperse the parralled light on focus mirror, and through focus mirror can focus dispersed light on the detector, the detector can transfer optical signal to electrical signal, and export to PC to readout spectrum.

What are important components of a spectrometer?

1st, incident slit, what's incident slit? it used to form point source.

2nd, collimating mirror

3rd, dispersing element, the most important component（grating or lens)

4th, focus optical system

5th, detector

6th, Signal Process Circuit

How many components make up of a spectrometer?

Fiber optic spectrometer is usually make up of 11 components:

SMA Fiber Port（Light Signal Entrance）

Entrance Slit

Long Pass Filter

Collimating Mirror

Color Dispersion Component（Grating）

Focus Reflectance Mirror

Collumn Mirror（Signal Intensity Enhanced）

2nd Order Sorting Filters

CCD/CMOS Detector

TEC +Temperature Sensor（Optional）

Signal Process Circuit

What is application of a spectrometer?

There are different application industries, such as measure colors, measure uv/vis absorbance spectrum, measure concentration of chemical components, measure emission spectrum, measure LED, measure thin film thickness, also monitor in process coating in vacuum chamber, oxygen concentration sensor, identify gemstones components, measure fluorescence and biomedical industry etc.

How to place an order of a spectrometer?

Optical fiber spectrometer is a customized product rather than a standard one, say, the manufacturer usually produces it according to customers demands, most spectrometers can be configured best performance by using different materials with different craftmanship or skills , finally commissioning to produce a spectrometer.

It's necessary to transfer specific spectral range, slit size, resolution, application and blazed wavelength to the manufacturer, so that the production manager can configure suitabale componens to reach up to the best performance for the customer.

It's needed to emphasize again, spectrometer a customized product! The best timing for customization shall be before production!

Before production, the product manager can configure differet components to reach up the best performance according to customer's requirement.

However after production, every performance has been fixed, and allow no further change or adjustment.

What are basic skills used to configure a spectrometer?

There are three basic skills used for configuring optic fiber spectrometer.

1st, wavelength range, by selecting different grating can customize any wavelength range, usually the more graing lines, the narrower the wavelength range, the higher the resolution. how to relize wavelength range plus high resolution, it can use mutli-channel combination.

2nd the sensitivity is decided by grating efficiency, incident fiber or slit size, optical lens peformance, collume mirror and detector sensitity.

3rd, optical resolution, how to improve optical resolution by using more grating lines, and narrower slit size.

4th, detector includes cooled CCD or uncooled CMOS, uv enhanced sensor, high SNR PDA, and IR range use InGaAs or Polyelectric

5th, multiorder diffraction effect can be eliminated by installing a long pass filter at the SMA entrance port, or add the 2nd order sorting filter in 2 types LVF or partition coating filter.

6th, select low stray light spectrometer

How many topology structure of optical path for a spectrometer?

There are commonly divided into 4 types of optical path, including crossed C-T, M-shape C-T, concave grating optical path, transmittance grating opitcal path.

Crossed C-T: ATP2000P,ATP2002, ATP2400, ATP1010, ATP5020P, ATP5040, ATP6500

M-shape C-T: ATP3030, ATP3034, ATP3330/4 ATP5030, ATP5034, ATP5330/4

Concave grating: ATP4230, ATP4020, ATP4050, ATP4070

let's see the M-shape optical path looks like a number "3", so our models uses the 3rd number "3" to indicate M-shape optical path models.

In generally, topology structure can decide resolution, sensitivity, stray light, and size of a spectrometer.

Crossed C-T topology structure employs better sensitivity and compact size.

M-shape C-T employs higher resolution and better stray light.

Concave grating optical path employs high stray light.

Which brand of detector used by Optosky spectrometer?

Optosky uses leading Hamamatsu detector origin in Japan, not only because the detector can decide sensitivity, SNR, dynamic range,max. wavelength range, cooled or not?

What is the advantages of cooled detector?

It can effectively reduce dark current, readout noise, and improve the stability.

How many cooling stages of spectrometer?

There are total 1-stage, 2-stage, 3-stage, and 4-stage cooled spectrometer.

How much does the detector cost?

Some detector of spectrometers cost decades of dollars, but others cost only few thousands, say cooled CCD cost much higher than uncooled CMOS.

What is the difference of CMOS vs CCD?

Compared CCD with CMOS, they are the same in the front optical and electrical transfer, electric charge collection, the difference is CCD transfer electric charge, it exports simulated signal, but CMOS internally transfer electric charge to voltage, it export digital signal. CCD export electric charge, CMOS export voltage. CCD export simulated signal, and CMOS export digital signal.

What is the working principle of spectrometer detector?

when a photon shoot on detector can generate electric charge, being accumulated and ionized till reading out. Take a vivid example can explain the priciple, when a photon shoot on detector, like the rain drops, after a period of time accumulation, every small bucket contain different rainwater, every pixels can hold different electric charge, when the rainwater is gradually poured out from this small bucket to shift register, finally pour them out to this big cylinder, by measuring total rainwater can know how much total electric chrages can transform to voltage. This gradually pour out rainwater process can explain working principle well.

When the light is shooting on the small bucket like the rain is coming down.

The small bucket collect rainwater indicate CCD detector electric charge.

Each small bucket indicate a pixel, every small bucket container indicates how much electric charge can be stored.

Pour them out gradually through shift register, And rainwater cylinder indicates CCD export amplifier.

What is the max. wavelength of spectrometer decided by the detector type?

Silicon dector wavelength range from 180nm-1100nm. K9 glass can start from 400nm, but the quartz can start from 180nm.

The InGaAs dector wavelength range from 900nm-2500nm.

Polyelectric detector wavelength range from 2.5-11um.

Why the detector sensitivity or photon efficiency play an important factor on the spectrometer sensitivity?

Take Hamamatsu detector s11510 and s10420 for example, both models can start from 200nm, but in 200nm s11510 quantum efficiency is 20%, but s10420 has 70%, if the application focus on uv range, s10420 employs higher sensitivity than s11510. However, we can see that in the NIR range 900-1100nm, s11510 employs higher quantum efficiency than s10420.

Different application focus on different wavelength can select accordingly.

What is SNR of spectrometer used for?

The SNR decides measurement precision, the minimum detection limit. In the quantitative analysis, SNR is a very important factor to consider.

What's the dynamic range of spectrometer used for?

The dynamic range equals the max. intensity output and readout noise/wavelength. It reflects the spectrum performance at

What is grating of a spectrometer used for?

The grating is an important component used to split lights, how to select a suitable grating can improve the spectrometer performance.

The grating lines selection can decide wavelength range and resolution, and the grating selection also relate to blazed wavelength can enhance certain wavelength sensitivity.

What is the slit of a spectrometer used for?

The slit size can affect resolution as well as sensitivity.

The slit size selection of 5, 10, 25, 50, 100, 200, 300, 500 μm.

The wider the slit, the higher sensitivity but poorer resolution, the narrower the slit, the better resolution but lower sensitivity.

What is the collumn mirror of a spectrometer used for?

The collumn mirror can be used for improve sensitivity about 3 times, but it can reduce resolution a bit. The collumn mirror can focus 80-90% energy on the detector enhanced intensity.

What is the high order diffraction filter used for?

It's the grating mechanical feature decides the 1st order diffraction, which is a must useful light, the grating feature decide in the 2nd, 3rd, and 4th order diffraction also have corresponding peaks. They are harmful lights can interference measure.

how to elimiate higher order diffraction of 2nd order, 3rd, and 4th orders? They are 2 ways to eliminate it.

1st, LVF, every areas go through different wavelengths,

the advantage provides smooth sepctrum shape, easy-to-produce,

the disadvantage of the cost is very high, customer have few selection of categories, can not change.

2nd, partition coating film, in 400nm appears light actually coming from 200nm, so we coat the right area, so that the 200nm light can not go through to the right areas, so the peaks can be eliminated. the advantage is low cost, many options for selection and receive customization.

But problems are in the front need passing uv light, but in the rear need blocking uv light, in the middle transit band can cause spectrum sunken.

What is the relationship of slit, sensitivity & resolution?

The smaller the slit size, the weaker sensitivity and higher resolution.

The wider the slit size, the higher sensitivity but poorer resolution.

When a line of fibers shoot on the slit can avoid energy waste, resulting in good resolution and sensitivity.

What are factors decide the spectrometer performance?

1st, wavelength range and resolution

2nd sensitivity

3rd,SNR

4th,Dynamic range

5th, cooled or uncooled

6th, stray light

7th, integration time & sampling speed

8th stability,

Temperature stability, how much intensity shift or wavelength shift

Long term stability

9th, algorithm

How to calculate the wavelength range?

The wavelength range equals end wavelength divide the start one, if the optical path topology is fixed, total wavelength range is decided by grating lines, the higher the grating lines, the shorter the wavelength range. the less the grating lines, the longer the wavelength range.

Once being fixed grating lines, the total wavelength range moving in one direction, so that total wavelength can move left or right.

Take ATP2000P 300-1100nm uses 500 lines grating for example,

range1000-300=700nm

If use 1200 lines grating, the range=500*700/1200=~291nm

What is the FWHM or optical resolution?

When we say spectrometer resolution usually use optical resolution, it's able to distinguish neighboring peaks, which is the most important parameter to measure light split capability.

It usually uses element lamp full width at half maximum to indicate, what's FWHM? this is peak heigth, obtain half height of full width, still some supplier use half height half width as resolution, obvious half height half width is not real optical resolution at all. Customer shall pay attention to this point. Optical resolution is defined by international standard, they are FWHM.

What is the pixel resolution?

Pixel resolution is a virtual definition, it's mainly decided by detector pixels, the more detector pixels, it can partially improve spectrometer resolution,

pixel resolution equals wavelength range divide pixels numbers, for instance, a spectrometer wavelength range 300-1000nm, range is 1000-300=700nm, and if detector pixels are 2048, so pixels resolution can be 700 divide 2048 equals 0.34,

What is the wavelength resolution

Wavelength resolution mainly applied to wavelength measurement, such as laser wavelength, fiber sensor. wavelength resolution is calculated by algorithm that is center gravity position of spectrum.

In numerical value, wavelength resolution is far smaller than optical resolution. According to our experience, wavelength resolution is only one tenth of optical resolution.

What are main factors can decide optical spectrometer resolution?

1st,optical path platform, M-shape C-T employs higher resolution, but crossed C-T employs higher sensitivity.

2nd Slit width, the narrower the slit width, the better the resolution, the wider the slit wdth, the poorer the resolution.

3rd, grating lines, the more grating lines, the higher the resolution, but if the more grating lines, the narrower the range, and the weaker the sensitivity.

4th, Detector pixels.

the smaller th detector pixels, the higher the resolution, Optosky use the detector pixels as much as 4096pixels, and ccd pixel width is only 7um, and ATP3034 nad ATP3040 uses 4096pixels. number "4" indicates 4096pixels CCD.

How to measure SNR of quantitative Raman?

1st, continuous acquisition, get a sample, set test condition of continuous acquisition>100times

2nd, peak distribution on time, obtain max. peak from every spectrum

3rd, calculate peak & noise Peak(i): average indn value 1, Noise (ơ): obtain MSE indn

4th, SNR=i/ơ

How is the detector cooling technology working?

Detector cooling technology, this is TEC, this is stage 1 cooling, this is stage 2 cooling, and this looks like tower is stage 3 cooling, what're these coolers working principle? It's actual PN knot, you can power on electricity to access from this side, here is cooling, and the heat is transferred to here is heating. heating can bring heat away can cool down the temperature. Through reverse current from left side, this position change to heating, and this side is cooling. If the current go in this side is cooling, opposit go in the other side is heating.

PN tube is here, TEC integrated inside make the sensor looks metal housing tougher, uncooled detector use plastic housing, the detector heat is relative small, no need to use metal.

What benefits can the cooled detector bring?

In the short integration time, the cooled or not has little influence, but the longer the integration time the cooled detector in -20 degree has smaller dark current, but in the room temperature has the bigger dark current.

next let's see dark noise and temperature curve, In -20 degree the dark noise is small, but in room tepmperature, the dark noise is so big, the dark current of uncooled detector is decades times higher than the cooled.

1st, dark current is smaller, the integration time can be longer, and 2nd, noise is small.

ATP6500 spectrometer can cooled down to -15 degree, and cooled integration time lasting 1.3hrs. ATP5020P spectrometer can cooled down to -5degree, and integration time last 10mins.

Why the cooled detector employs higher performance?

Let's take the ATP6500 for example, when cooled down to 100ms, dark current is only 80counts, 16bit A/D, noise is 7, when the integration is 10s, the dark current is 245, when the integration time is 10s, the noise is only 10, when the integration time is 60s, the dark current is only 1100, and the noise is only 30, it's ease to run over a hour, and noise level is so small, that's why the ATP6500 cost higher but quite reasonable for such good performance.

Why the cooled spectrometer size is longer?

The cooled spectrometer has longer size for being installed fans inside and ventilation port, 2nd cooled spectrometer has bigger power consumption, so it has external power port, common spectrometer can use USB connect, but cooled spectrometer shall have power port.

Why Optosky's spectrometers employs higher reliability than competiors?

Some competitors' optical bench being fasten on metal platform, the optical chamber and electrical chamber are completely divided, which can avoid electrical board volatile chemical polluting optical components, this optical bench is fasten direct on pcb, but Optosky optical bench is fasten on metal platform, you can see the alluminum alloy thermo expansion coefficiency is only 18, but pcb is over 155, the reliability has improved over 10 times.

Let's see our spectrometer test result that the intensity stability change rate is only 0.37%, long time stability is only 0.14% also very good figure testify high stability.

What are application of spectrometers?

1st, Environmental industries:

UV smoke analysis

Multi-parameters online water quality analysis

No reagenet online water quality analysis

2nd, Industrial Inspection:

Colorimeter, colors sorting

Emissivity,Transmittance Measure

Laser wavelength monitor

LED color temp sorting

Film thickness measure meter

Glass thick measure meter